Acetazolamide Treatment of Hypokalemic Periodic Paralysis Probable Mechanism of Action Frederic
Q. Vroom, MD;
Maureen A. Jarrell; Thomas H. Maren, MD
Following administration of glucose and insulin to three patients with hypokalemic periodic paralysis, serum K fell 1.9 mM. After administration of acetazolamide, 250 mg four times daily, serum K fell 0.9 mM, a substantial difference. In normal persons glucose and insulin lowered serum K 0.5 mM, and this was not changed substantially by acetazolamide. The metabolic acidosis induced by the drug appears to be responsible for the change in decrement of serum K and for the amelioration of symptoms in the patients. The findings agree with earlier reports that metabolic acidosis lowers the rate of entry of K\m=+-\into muscle, thus opposing the heightened or pathological entry of K\m=+-\into muscle cells during attacks of the disease. (Arch Neurol 32:385-392, 1975)
normal volunteers and patients with hyperkalemic periodic paral¬ ysis, acetazolamide administration re¬ duced the influx of K> from serum to red blood cells,1·2 and because the experiments established a steady state, efflux of K> also was reduced. This effect was small and not entirely consistent, yet it suggested that the
In
drug might prevent paralysis by reducing Kr flux into or out of red blood cells or other tissues. Hyperkalemia in man or experimental animals invoked by K* administration or by exercise also was lessened by acetazol¬ amide, in terms of both rate of
increase and absolute level.3 In these studies, blood glucose decreased dur¬ ing attacks of paralysis; this effect also was minimized by acetazolamide, suggesting an alteration in glucose metabolism. When the magnitude of hyperkalemia and hypoglycemia was modified, the severity of the clinical
Accepted for publication Sept 3, 1974. From the departments of pharmacology and therapeutics and of medicine (neurology), University of Florida College of Medicine, Gainesville.
Reprint requests to Department of PharmacolTherapeutics, University of Florida College of Medicine, Box 728, JHM Health Center, Gainesville, FL 32610 (Dr. Maren). ogy and
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attack was lessened considerably by acetazolamide. The periodic paralyses appear to be diseases in which serum K* is un¬ stable; diverse stimuli trigger attacks, and there are increased K+ fluxes between serum and other cells. Other abnormalities include dilation of sarcoplasmic reticulum, with accumula¬ tion of glycogen, vacuolization of muscle, and decreases in skeletal muscle membrane potentials. De¬ creased calcium-binding and some en¬ zyme activities of sarcoplasmic retic¬ ulum have been reported for three cases of thyrotoxic hypokalemic peri¬ odic paralysis and one sporadic case.46 Other possible derangements of ionic pumping of sodium and potassium or carbohydrate metabolism have long been suspected.7 The present paper describes a black family with hypokalemic periodic pa¬ ralysis, treatment with acetazolamide and other diuretics, and studies to define the action of acetazolamide and the mechanism triggering attacks. (This is the second black family with this disease to be reported; the first was described by Talso et al.s) The chief finding was that, in the provoca¬ tive test (insulin and glucose loading), which lowers serum 1, acetazolamide notably blunted the hypokalemic ef¬ fect.
Table 1.—Clinical Data Patient 1 27, M 22
Age (yr), sex Age at onset, yr
on
Patients
Patient 2 31, M 20
Treatment*
Attacks/yr
Control
Mild Moderate
Control
Rx 2
10
t 52 12 155 105
Severe
Blood pressure,
mm
Hg
140 100
Precipitating factors Exercise Rest
Emotional stress
High-carbohydrate diet Ethyl alcohol Cold Serum concentration Sodium, mM Potassium, mM CO„ mM CPK (normal, 3 to 35 units) Aldosterone, /¿g/24 hr
124 86
Yes Yes No Yes No No Control 136 3.6 26
Yes Yes No No No No Control 134 3.8 28 515
Rx 132 3.4 15
Patient 4 35, M
Patient 3 33, M 12
Control
Rx 1
RxA 12
1Í
M RxM 0
Control
t
Dy RxDy 2
RxA 0
50
10
24
150 100
1_27 93
Control
Rx 132 4.0 23
147 4.8 28 556
112 70
Yes Yes Yes Yes Yes No RxA 150 3.6 21
158 118
138 98
Yes Yes No No No No Control 136 4.6 22 316
RxDy 140 4.3 27
(normal, 2 to 26)
Thyroxine, ^g/100 mi (normal, 3.8
*
to
8.3)
A, Acetazolamide, 250
6.6 mg every six
chlorothiazide, 25 mg, one dose per day. t Patients had chronic mild weakness restricted
These studies, coupled with the known capacity of acetazolamide to produce metabolic acidosis,9 the ef¬ fects of acidosis that reduce K* influx from serum to muscle,1011 and the increased K* entry from serum to muscle during attacks,12·13 suggest the following mechanism for the benefi¬ cial effects of the drug: Attacks are usually associated with greatly increased K> entry from serum to muscle, so that serum K+ drops about 2 mM. Acetazolamide induces a metabolic acidosis, the effect of which is to decrease K+ influx from serum to muscle, thus opposing the abnormality that causes
paralysis.
REPORT OF CASES Four brothers a
were
4.0
hours. M, Methazolamide, 50 to 100
studied, members of
family whose eight siblings included one
affected sister, one unaffected brother, and two unaffected sisters. The father (deceased) reportedly had episodic weak¬ ness; the mother is alive and well with no signs of weakness. Attacks were defined as mild when weakness was noticed by the patient or detectable on examination but not appar-
to one or two
ent to
a
6.8
5.3 mg every
eight hours. Dy, Dyazide: triamterene, 50
mg,
+ hydro-
limbs.
casual observer. Moderate attacks
produced limb or trunk weakness apparent to a casual observer during everyday activ¬ ities, but not severe enough to prevent sitting, standing, or walking. Severe attacks prevented these activities. At no time was respiration impaired. The aver¬ age duration of moderate or severe attacks was one or two days; mild attacks often
lasted weeks or months. The four patients were evaluated for the following (Table 1): complete blood count; erythrocyte sedimentation rate; serum cho¬ lesterol, calcium, and phosphorus; creatine
phosphokinase (CPK); thyroxine as T4; two-hour postprandial blood glucose; VDRL test and electrophoresis; creatinine clearance and urinalysis; chest x-ray films and intravenous pyelogram; electromyo¬ graphy and nerve stimulation. Results of these studies were normal unless noted otherwise. Twenty-four-hour urinary aldosterone level was obtained after seven days of a high sodium chloride diet containing at least 8 gm of sodium per day. Urinary renins were checked each morn¬
ing. Case 1.-Patient 1 was strong and muscular in his youth. At age 22, on entering the Marine Corps, his first attack of generalized weakness occurred after running five miles. The weakness persisted for three weeks. Thereafter, attacks were
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precipitated by
rest
following prolonged
calisthenics. In August 1972, he was a muscular, 27year-old man with excellent strength and normal reflexes. Results of a biceps muscle biopsy were normal except for a few scat¬ tered, small, rounded muscle fibers, stained by Gomori trichrome, which were both type I and type II fibers by histochemical stain¬ ing. In quantitative electromyography of the opposite biceps, the mean action poten¬ tial duration was 11.7 msec (normal 10.4 msec ± 20%). Ulnar motor nerve conduc¬ tion was normal at 62 meters/sec in the wrist-elbow segment; ulnar sensory nerve conduction was also normal at 56 meters/ sec. Blood pressure and attacks of paralysis were both controlled over the subsequent II months by acetazolamide, 250 mg four times a day (Table 1). Case 2.-Patient 2, 31 years old, had weakness of elbow flexors and extensors and hip flexors. Tendon reflexes were diminished but present. Muscle biopsy results were normal except for minimal type II muscle fiber atrophy. Results of electromyography and motor and sensory nerve conduction studies were normal. Oral acetazolamide, 250 mg four times daily, resulted in normal strength, return of reflexes, and virtual freedom from attacks for 12 months (Table 1). Case 3.-Patient 3,33 years old, although =
t • a
+
°
5
or. =
E
Glucose-Insulin
Acetazolamide
•
,
dose
single
o
Moderate Restricted Weakness
Test 2 Before Acetazolamide
mt
Moderate Generalized Weakness
1.8 1.6 1.4 1.2 1.0
1.6 1.4 1.2 m ^ ·| 1.0 rx £ E
+
ol% +"
4.0 3.5 3.0 2.5
¡1 w
0,100 »
50
JS S
i &°
I
< a.
E
u
treatment
t+
Mild Generalized Weakness
o ° o
2.
,
-+++
I 150
_
During Acetazolamide chronic
Mild Restricted (One Limb) Weakness
Test 1 Before Acetazolamide
4.5 4.0 3.5 3.0 2.5
n
Test
+
E°
4.0 3-5 3.0
g
150
8°
loo
E
so
-2
m O
C»
,_
ifE 3 uj
,
co
4.0 3.5
.
O « _l_I_I_I_l_I
0
30
90
I_I_l_I_l_u
150
210
270
330
O «
0
Minutes
muscular and well developed, had minimal weakness so that a push-up was done with difficulty. Tendon reflexes were hypoactive in the arms and absent in the legs. There was an abnormally short mean duration of motor unit potentials (5.4 msec) in the biceps when strength was reduced to just being able to overcome gravity. No spontaneous electrical activity was noted on sampling numerous proximal and distal limb muscles during the attack. Nerve conduction was normal except for a decrease in the amplitude of the evoked muscle action potential. Ten and fifteen days after initiating oral administration of acetazolamide, 250 mg four times daily, right and left renal colic occurred. Some gravel was passed. On examination two weeks later, while still on acetazolamide, serum uric acid was 7.8 and 8.5 mg/100 ml (before acetazolamide ther¬ apy, serum uric acid level had been 5.5 and 5.8 mg/100 ml; normal, 3.4 to 7.8 mg/100 ml); the urinary uric acid value was 700 mg/24 hr (normal, less than 1,000 mg); 24-
90
150
210
270
330
Minutes
Fig 1.—Metabolic studies in patient (case 3) with familial periodic paralysis. Acetazolamide, 500 mg, was administered
triceps
30
intravenously. Patient was tested twice before (A) and once during chronic acetazolamide treatment, five weeks later (B).
urinary calcium value was 85 mg (normal, less than 250 mg); and urinary pH was 5 to 6. Roentgenographic examination for renal calculi showed no abnormality. The episode was attributed to elevated plasma and tissue uric acid due to inhibi¬ tion of uric acid secretion by acetazola¬ mide.11 The gravel was presumably the
hour
radiolucent uric acid. Acetazolamide was discontinued and orally administered methazolamide, 100 mg initially and later 50 mg every eight hours, was substituted because it probably does not block urinary excretion of uric acid." Attacks of paral¬ ysis were then well controlled (Table 1), and no further episodes of renal colic occurred during the subsequent 12 months. Acetazolamide (500 mg in two minutes) was administered intravenously during an induced attack (Fig 1). The course of weak¬ ness and recovery appeared to be unaf¬ fected by this dose. Case 4.-Patient 4 was well developed at 35 years of age and exhibited minimal hip
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flexor weakness and areflexia. Results of a right biceps muscle biopsy were normal except for a few scattered, small, round muscle fibers that were both type I and type II by histochemical stains. Electro¬ myography and nerve conduction tests showed no abnormalities. Serum electrophoresis showed a hyper-/?- and diffuse hyper-y-globulinemia (1.4 and 1.8 gm/100 ml, with a normal of 0.6 to 1.2 and 0.6 to 1.6
gm/100 ml, respectively). Dyazide (triam-
terene, 50 mg, and hydrochlorothiazide, 25
mg), given orally once daily, resulted in normal strength and reflexes, as well as good control of attacks of paralysis and hypertension for nine months, after which time equally good control was obtained with orally administered acetazolamide, 1 gm per day (Table 1). None of the patients received supple¬ mental potassium. METHODS The study included normal individuals and these four patients. Control subjects
Table 2.—Effect of Glucose-Insulin on Serum K+ in Three Patients With Hypokalemic Periodic Paralysis: Alteration of Response by Acetazolamide Before Glucose-Insulin
pH
C02
K+
After Glucose-Insulin
Ch pH P04= Control (n=5) 102.2 3.2 7.42
C02
K+
CI"
23.8 0.9
2.44 0.14
102.4 1.0
2.7 0.2
3.07 0.12
111.0 2.9
3.7j
P04=
*
Mean :SE
7.42 0.01
25.2 1.2
Mean :SE
7.36 0.02
22.6 1.2
4.36 0.13
0.7
0.1 0.01 Acetazolamide Treatment (n=3)f 4.00 105.7 7.33 20.3 3.8t 0.20 2.0 0.03 1.5 ...
Two of the patients were tested twice. t Plasma concentrations of drug ranged from tions ranged from 14/jg/ml to 15/ig/ml. $ One test only. *
healthy, paid volunteers, two men and two women, ages 22 to 25 years. At 8 am, an were
18-gauge scalp vein needle was placed in the cubital vein, and the initial blood samples were drawn. One hour later glucose (1.75 gm/kg, orally as Glucola) and insulin (regular, 20 units intramuscularly) were administered. Blood samples were drawn every half hour for the duration of the experiment and analyzed for pH,
sodium, potassium, chloride, bicarbonate, glucose, and inorganic phosphate. Samples
also drawn every 90 minutes for determination of red blood cell potassium influx. Following the initial control study, each volunteer was placed on acetazo¬ lamide (250 mg four times a day). After one week, the volunteer returned and was admitted to the hospital, and the test was repeated. Procedures were fully explained to the normal volunteers and to the patients, and written consent was ob¬ tained. The physicians in attendance were ready for measures to counter respiratory failure, although, to our knowledge, this has never been reported following glucoseinsulin administration. Serum sodium and potassium levels were determined by flame photometry, and serum chloride and bicarbonate by an auto¬ mated system of chemical analysis. Blood glucose was measured by blood sugar kit, blood pH by blood gas analyzer, and serum phosphate by the Whitehorn modification of Bell-Doisy method.15 Blood thyroxine content was obtained by means of a T4 diagnostic kit; creatine phosphokinase val¬ ue was determined by the Rosalki assay; aldosterone level was obtained by radioimmunoassay. Potassium influx to red cells was determined in triplicate by modifica¬ tion of a method described previously.' Modifications included a reduction in volume of the whole cell suspension to 15 ml and a reduction of potassium 42 to 5 microcuries per millimol K* of external media. The isotope was in an acid solution. were
3fig/ml
to
16/tg/ml. Red
blood cell concentra¬
Serum drug levels of acetazolamide were determined by the method of Maren et al."
Patients were evaluated frequently dur¬ ing the experiment for clinical changes. Electrocardiograms and vital capacities were monitored. Weakness was always associated with a decrease or absence of tendon reflexes in the muscle involved. Weakness was considered mild if gravity could be overcome and the force of resist¬ ance was good or very good, but definitely less than the attack-free state. With moderate weakness, the force of resistance was
weak; with
severe
weakness, gravity
could not be overcome. Attacks were restricted if weakness was only in one limb and were generalized if weakness involved more than one limb. The limb used for obtaining blood samples was not tested.
RESULTS Metabolic Findings in Patients
Before drug (Fig 1, A) the patient was in normal acid-base balance, serum pH 7.41 and C02 28 mM. During the test, while receiving the drug, (Fig 1, B), serum pH was 7.39 and C02 21 mM. During drug treatment, serum K+ was slightly reduced (to 3.6 mM), and blood glucose and serum phos¬ phate were unchanged. The flux stud¬ ies on entry of K* to red cells (before glucose-insulin) showed that acetazo¬ lamide reduced flux about 20%, in agreement with other data on normals and patients with hyperkalemic peri¬ odic paralysis.1·2 Glucose-insulin lowered serum K* 2.0 and 1.8 mM in two tests before the drug (Fig 1, A). In the same test during drug treatment, the K* decre¬ ment was 0.6 mM (Fig 1, B). Table 2 extends the principal find-
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ing of Fig 2 to two other patients, showing again that the effect of glucose-insulin on serum K* is sub¬ stantially lessened by acetazolamide. There is also the suggestion that acetazolamide modifies the fall in serum
P04
=.
The effect of the glucose-insulin test on the influx of K* to red cells was equivocal in the experiments of Fig 1. Before treatment with acetazo¬ lamide (Fig 1, A), one test showed no change in K+ influx, the other a trans¬ ient decrease. During treatment with acetazolamide (Fig 1, B), K* influx lowered but glucose-insulin was caused no further change. (Further data on this point are given in Fig
3.)
Glucose-insulin produced marked weakness in the two control tests (Fig 1, A); this was not altered by intrave¬ nous administration of acetazolamide. After long-term acetazolamide ad¬ ministration, there was much less weakness following glucose-insulin,
although weakness was abolished (Fig 1, B).
not
entirely
The effect of acetazolamide on the blood glucose curves following glu¬ cose-insulin is shown in Fig 2. The drug reduced the glucose level and shortened recovery time in two of the
patients.
Metabolic Findings in Normal Volunteers
The four normal persons developed all the characteristics of chronic carbonic anhydrase inhibition: lower¬ ed serum pH, C02, and K+, and normal Na+ and P04= (Table 3). There was no respiratory acidosis. In these normal subjects, the effect of glucose-insulin on serum K* was slight (Table 3) compared to the patients (Table 2). The fall in serum K+ averaged 0.6 mM before drug and 0.42 mM during treatment. This is not a significant difference, but in two of the four, (Fig 3, top right and bottom right) the drug did appear to reduce the decrement in K* (not shown in the
figure). Long-term administration of aceta¬
zolamide reduced K+ influx into normal red cells (Fig 3), as in the patients (Fig 1). Glucose-insulin in¬ creased K> flux into red cells, and
acetazolamide
opposed this effect (Fig
3).
180
Differences in blood glucose follow¬ ing glucose-insulin, before and after acetazolamide, were small. Acetazo¬ lamide seemed to elicit a higher peak and more rapid fall than observed in the controls (Fig 4). More work is needed to confirm this.
130-
Therapeutic Effect of Acetazolamide in Hypokalemic Periodic Paralysis Relation to Other Drugs Used.—All four patients were much improved by acetazolamide. Only occasional mild attacks were observed or reported. Some mild weakness persisted in case 4 during treatment, but much less than before treatment. Serum HC03- and acetazolamide levels during one year usually showed an acidosis and presence of drug, although these were occasionally less than expected, indicating some failure of compliance (Table 4). The data were not adequate to correlate serum pH and HC03- at any given time with either clinical effects or protection against K> fall in serum. However, during the glucose-insulin tests of Fig 1 and Table 2, there was always some acidosis during acetazolamide treat¬
230-
E
180-
130
180
ment.
The minimum effective dose of acetazolamide for control of this disease cannot be determined preci¬ sely from our data, but it is probably 500 to 1,000 mg daily, in single or divided doses. This is the dosage usually given for glaucoma and yields full inhibition of carbonic anhydrase.9 Methazolamide appears to be effec¬ tive at a lower dose, as in glaucoma. In our view, methazolamide might pres¬ ently be the drug of choice, since it probably will not cause uric acid stones14
(case 3).
The beneficial effect of Dyazide (case 4) is not due to carbonic anhy¬ drase inhibition or to metabolic acido¬ sis. It is likely that the K+-retaining and NaMosing effect of this combina¬ tion is responsible.8 COMMENT
The effects of glucose-insulin, which lower serum K* 2 mM in patients with hypokalemic familial
130-
Minutes
Fig 2.—Blood glucose content in familial periodic paralysis following glucose-insulin (arrows). Solid lines, Before acetazolamide. Dashed lines, During acetazolamide. Top, Case 1. Center, Case 2. Bottom, Case 3.
periodic paralysis,
were taken as a model for attacks of the disease. The effects of acetazolamide were studied in this context. The main finding relevant to the effect of acetazolamide on the disease is that of stabilizing serum K+ against the fall. Since acidosis reduces the
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influx of K+ into muscle (and probably other sites as well),10·11 it is reasonable to assume that acetazolamide works through the induction of acidosis; the acidotic state opposes the tendency of K+ to leave serum for intracellular sites in normals and in patients with this disease.
2.0
1.8 1·6
I
O
1.4
m
er
1.2
+ :
2.0
»
o
J
1.8
I
1.6 1.4 1.2
120
240
360
120
240
360
Minutes
Fig 3.—Potassium influx into red cells taken from normal volunteers after glucoseinsulin (arrows). Solid lines, No drug. Dashed lines, After one week receiving acetazol¬ amide orally. Vertical lines show standard error of mean of four flux measurements. Top left, 22-year-old woman. Top right, 21-year-old man. Bottom left, 23-year-old woman. Bottom right, 25-year-old man. Table 3.—Effect of Glucose-Insulin on Serum and Red Blood Cell K+ in Four Normal Volunteers: Effect of Acetazolamide* After Glucose-Insulin
Before Glucose-Insulin Serum
Serum
RBC
pH
CO,
Na+
7.43
21
138
4.0
7.36
li
140
3.7
pH
P04=
CO,
Control 7.45 22 Acetazolamide Treatment 3.6 91 7.37 15 3.6
99
RBC
Na+
PO.
137
3.4
3.0
99
137
3.3
2.6
92
The potassium decrement in control series (—0.6 mM) is not statistically different from that (—0.4 mM) in the treated. Mean data (mM). t Plasma levels were 8,ag/ml to 18/¡g/ml. *
This mechanism invoking metabolic acidosis appears to fit all the facts at hand, in the present and other studies. Direct action of acetazolamide at the muscle membrane had been hard to visualize, since there is no carbonic anhydrase in muscle and since we have shown that there is no direct effect of the drug on K* exchange in isolated muscle" or in red blood cells in vitro.1 Griggs et al suggested that acidosis might be the key factor.18 To test this, they discontinued acetazolamide and administered NH4C1 to one patient. Unfortunately, the dose was too small, the metabolic acidosis achieved by acetazolamide was actually dissipated
during NH4C1 treatment, and the attacks returned. This critical experi¬ ment remains to be done, but would require some 10 gm or more of NH4C1 per day. Viskoper et al19 found that intrave¬ nously administered NH4C1 (2 gm) improved the electromyogram results of one patient and NaHC03 (1 mEq/ min x 60 min) caused deterioration of the electromyogram results, with a frank paralytic attack.'9 These obser¬ vations are in qualitative agreement with our data and conclusions, but further work remains to be done, including acid-base and K* measure¬ ments
following NH4C1. Furthermore,
acidosis and alkalosis may also have
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effects directly on the disease unre¬ lated to K> movement, as suggested by Viskoper et al's'9 NaHCO:, experi¬ ment, in which paralysis ensued with normal serum K* levels. The argument in favor of the role of metabolic acidosis is supported by the fact that, in a dose that completely in¬ hibits carbonic anhydrase, intrave¬ nously administered acetazolamide (500 mg) has no perceptible effect on an induced attack (Fig 1, A), whereas equivalent or lower serum concentra¬ tion during chronic treatment does ameliorate the symptoms. Viskoper et al19 reported that intravenously ad¬ ministered acetazolamide abolished an attack, but this attack was precipi¬ tated by NaHCO„ which was stopped (with corresponding drop in serum HCOr) when acetazolamide was giv¬ en (Fig 3 of their study). We found, in agreement with Grob et al,2" that glucose-insulin produced only a modest hypokalemic effect in normals. The effect of acetazolamide in this situation is, thus, difficult to observe, and we obtained only a small difference in the K* decrement between control and treated groups. Quantitative considerations of the overall K* flux from serum to muscle as affected by this disease and by acetazolamide have not been made. A model calculation follows: An adult with 30 kg of muscle and a flux rate for K* of 50 millimols/kg/ hr21 moves 1,500 millimols per hour in and out of muscle, from a serum source of 12 millimols (4 mM x 3 liters of serum) or an extracellular pool of 60 millimols (4 mM x 15 liters). In hypo¬ kalemic familial periodic paralysis, the attack reduces serum or extracel¬ lular K* from 4 to 2 mM in about two hours, which implies that the muscle influx increases (from the extracel¬ lular fluid source) 15 millimols per hour, or 1%. Thus, a relatively small change appears to be the pathophysiological basis for the disease. This lends credence to the likelihood that a rela¬ tively small metabolic alteration (ie, slight acidosis) might reverse it. The acidosis, as previously shown for humans with unimpaired respira¬ tion, is metabolic and partially com¬ pensated.22 Serum HCO.r is lowered some 5 mM and pH 0.1 unit. It is
to note that animal data show that an intracellular (in muscle) acidosis results from carbonic anhydrase inhibition.23 Serum K+ in the present study is low normal in both patients and the normal volunteers. We have confirmed our earlier find¬ ing2 that acetazolamide in vivo re¬ duces flux of K> from plasma to red cell. This may also reasonably be ascribed to the metabolic acidosis. However, this flux is so much smaller (about one thirtieth) than that for muscle that it is unlikely that altera¬ tions play a part either in the cause or treatment of the disease. Although acetazolamide may act by its effect on K+ entry to muscle, this leaves unexplained why, during an attack, it is the resting muscle membrane potential that is abnormal, rather than the ratio of K+ between plasma and muscle.7 It would also be of great interest to explore the rela¬ tion of the present findings to Zierler's suggestion that the defect in hypokalemic disease is failure of acti¬ vation of Na* conductance in the sarcolemma.24 Acetazolamide could correct this, if such a change were pH sensitive, either directly or through an effect on K+ entry. Our data following glucose-insulin show that acetazolamide tends to reduce the peak level of blood glucose (Fig 2) and to bring the level back to normal more rapidly than in untreat¬ ed controls (Fig 4). It appeared that the glucose was more rapidly metabol¬ ized or distributed; it is doubtful that the effect of insulin was enhanced, since acidosis causes relative resis¬ tance to insulin.25 We also show some impairment of glucose tolerance in patients with hypokalemic disease (Fig 2 and also case 4, not shown). The significance of these changes in rela¬ tion to the cause or treatment of the disease is not clear. Our clinical findings agree with others 18·19 that acetazolamide is effec¬ tive in the treatment of hypokalemic periodic paralysis, and our idea that acidosis is the mechanism is related to the finding that dichlorphenamide, a carbonic anhydrase inhibitor of dif¬ ferent structure but also capable of inducing acidosis, is effective.26 The relation of these findings to the
important
Minutes 4.—Blood glucose changes in four normal volunteers following glucose-insulin before (solid lines) and after (dashed lines) one week of acetazolamide treatment. Base¬ line glucose level before injection of glucose-insulin was 77 mg/100 ml in untreated and 78 mg/100 ml in treated persons. Data are means for all persons. Standard errors of means are shown at 30 to 90 minutes.
Fig
Table 4.—Drug and Electrolyte Measurements in Long-Term Treatment of Familial Periodic Paralysis Acetazol-
Serum* RBC* K+
amide,
/¿g/ml
pH
CO, 15 25 29 22
3.4 3.4 4.5 4.2
93 120 119
65
7.44 7.42 7.30
23
4.0 4.1 3.9
91 101 99
50
97 120
14 12
Notes (for 1/17 and 11/8)
Patient 1
9/14/72 11/16/72 1/17/73 11/8/73
0 2 4
probably took drug the day he came to the hospital after lapsing at home; thus
Patient
minimal or absent electro¬ lyte effect
Patient 2
9/14/72 11/16/72 1/17/73 11/8/73
7.41 7.40 7.43
28 25
7.31 7.44
21 25
3.6 5.6
23 11/8/73 7.40 expressed in mM.
4.4
18 12 3
4.1
As above for
patient 1
on
these dates
Patient 3
12/1/72 1/17/73 Patient 4 Data
beneficial effect of acetazolamide in
Aw/perkalemic periodic paralysis is not
clear. There are some, but still insuffi¬ cient, data on the induction of attacks following K+ administration or other stimuli in the presence of acetazolam¬ ide.2·3 Since both hydrochlorothiazide (not a carbonic anhydrase inhibitor in the doses used) and acetazolamide appear to control the hyperkalemic form,2" it is probable that both act by the chief pharmacological property they share, kaluresis. Preliminary data in this laboratory suggested that the elevation of serum K> in hyperkal¬ emic paralysis was modified by aceta-
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zolamide,' but more studies are need¬ ed, particularly since the induction of
acidosis should yield the reverse effect. Considering the two diseases as variations of an entity, we propose that the major effect of acetazolamide is to stabilize muscle membranes against abnormal K+ fluxes, but the intimate details of such processes remain to be discovered.
This study was supported by Public Health Service research grants GM 16934 and NS-528114.
This study was carried out in the Clinical Research Center NIH RR-82-12 at the University of Florida, Gainesville.
1. Hoskins B, Jarrell MA, Maren TH: Effects of carbonic anhydrase inhibitors on potassium exchange in human red blood cells. Arch Int Pharmacodyn Ther 209:186-192, 1974. 2. Hoskins B, Maren TH, Vroom FQ, et al: Acetazolamide and potassium flux in red blood cells: Studies in patients with hyperkalemic periodic paralysis. Arch Neurol 31:187-191, 1974. 3. Hoskins B, Vroom FQ, Jarrell MA: Hyperkalemic periodic paralysis: Effects of potassium, exercise, glucose, and acetazolamide on blood chemistry. Arch Neurol, to be published. 4. Takagi A, Schotland DL, DiMauro S, et al: Thyrotoxic periodic paralysis: Function of sarcoplasmic reticulum and muscle glycogen. Neurology 23:1008-1016, 1973. 5. Au K-S, Yeung RTT: Thyrotoxic periodic paralysis: Periodic variation in the muscle calcium pump activity. Arch Neurol 26:543-546, 1972. 6. Ionasescu V, Schochet SS, Powers JM, et al: Hypokalemic periodic paralysis: Low activity of sarcoplasmic reticulum and muscle ribosomes during an induced attack. J Neurol Sci 21:419\x=req-\ 429, 1974. 7. Hofmann WW, Smith RA: Hypokalemic periodic paralysis studies in vitro. Brain 93:445\x=req-\ 4x74, 1970. 8. Talso PJ, Glynn MG, Oester YT, et al: Body composition in hypokalemic familial periodic paralysis. Ann NY Acad Sci 110:993-1008, 1963. 9. Maren TH: Carbonic anhydrase: Chemistry, physiology and inhibition. Physiol Rev 47:595-781,
1967. 10. Scribner BH, Fremont-Smith K, Burnell JM: The effect of acute respiratory acidosis on the internal equilibrium of potassium. J Clin Invest 34:1276-1285, 1955. 11. Keating RE, Weichselbaum TE, Alanis M, et al: The movement of potassium during experimental acidosis and alkalosis in the nephrectomized dog. Surg Gynecol Obstet 96:323-330, 1953. 12. Grob D, Johns RJ, Liljestrand A: Potassium movement in patients with familial periodic paralysis. Am J Med 23:356-375, 1957. 13. Zierler KL, Andres R: Movement of potassium into skeletal muscle during spontaneous attack in family periodic paralysis. J Clin Invest 36:730-737, 1957. 14. Maren TH: Renal carbonic anhydrase and the pharmacology of sulfonamide inhibitors, in Herken H (ed): Handbook of Experimental Pharmacology. New York, Springer-Verlag, 1969, vol 24, pp 195-256. 15. Peters JP, Van Slyke DD: Quantitative Clinical Chemistry: Methods. Baltimore, Williams & Wilkins Co, 1932, vol 2. 16. Maren TH, Ash VT, Bailey EM: Carbonic anhydrase inhibition: II. A method for determination of carbonic anhydrase inhibitors, particularly of Diamox. Bull Johns Hopkins Hosp 95:244\x=req-\ 255, 1954. 17. Jarrell MA, Maren TH: The effect of acetazolamide on the transport of potassium and rubidium into guinea pig diaphragm. Proc Soc Exp Biol Med 146:1119-1121, 1974.
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18. Griggs, RC, Engle WK, Resnick JS: Acetazolamide treatment of hypokalemic periodic paralysis. Ann Intern Med 73:39-48, 1970. 19. Viskoper RJ, Licht A, Fidel J, et al: Acetazolamide treatment in hypokalemic periodic paralysis: A metabolic and electromyographic study. Am J Med Sci 266:119-123, 1973. 20. Grob D, Liljestrand A, Johns RJ: Potassium movement in normal subjects. Am J Med 23:340-355, 1957. 21. Calkins E, Taylor IM, Hastings AB: Potassium exchange in the isolated rat diaphragm: Effect of anoxia and cold. Am J Physiol 177:211\x=req-\ 218, 1954. 22. Birzis L, Carter CH, Maren TH: Effect of acetazolamide on CSF pressure and electrolytes in hydrocephalus. Neurology 8:522-528, 1958. 23. Maren TH, Ellison AC: The effects of acetazolamide and amiloride on tissue electrolytes, with reference to the teratogenesis of carbonic anhydrase inhibition. J Pharmacol Exp Ther 181:212-218, 1972. 24. Zierler KL: Speculations on hypokalemic periodic paralysis. Am J Med Sci 266:131-133, 1973. 25. Mackler B, Lichtenstein H, Guest GM: Effect of ammonium chloride acidosis on action of insulin in dogs. Am J Physiol 166:191-198, 1951. 26. McArdle B: Metabolic and endocrine myopathies, in Walton JN (ed): Disorders of Voluntary Muscle. Boston, Little Brown & Co, 1969, pp 607-638.
Q. Vroom, MD;
Maureen A. Jarrell; Thomas H. Maren, MD
Following administration of glucose and insulin to three patients with hypokalemic periodic paralysis, serum K fell 1.9 mM. After administration of acetazolamide, 250 mg four times daily, serum K fell 0.9 mM, a substantial difference. In normal persons glucose and insulin lowered serum K 0.5 mM, and this was not changed substantially by acetazolamide. The metabolic acidosis induced by the drug appears to be responsible for the change in decrement of serum K and for the amelioration of symptoms in the patients. The findings agree with earlier reports that metabolic acidosis lowers the rate of entry of K\m=+-\into muscle, thus opposing the heightened or pathological entry of K\m=+-\into muscle cells during attacks of the disease. (Arch Neurol 32:385-392, 1975)
normal volunteers and patients with hyperkalemic periodic paral¬ ysis, acetazolamide administration re¬ duced the influx of K> from serum to red blood cells,1·2 and because the experiments established a steady state, efflux of K> also was reduced. This effect was small and not entirely consistent, yet it suggested that the
In
drug might prevent paralysis by reducing Kr flux into or out of red blood cells or other tissues. Hyperkalemia in man or experimental animals invoked by K* administration or by exercise also was lessened by acetazol¬ amide, in terms of both rate of
increase and absolute level.3 In these studies, blood glucose decreased dur¬ ing attacks of paralysis; this effect also was minimized by acetazolamide, suggesting an alteration in glucose metabolism. When the magnitude of hyperkalemia and hypoglycemia was modified, the severity of the clinical
Accepted for publication Sept 3, 1974. From the departments of pharmacology and therapeutics and of medicine (neurology), University of Florida College of Medicine, Gainesville.
Reprint requests to Department of PharmacolTherapeutics, University of Florida College of Medicine, Box 728, JHM Health Center, Gainesville, FL 32610 (Dr. Maren). ogy and
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attack was lessened considerably by acetazolamide. The periodic paralyses appear to be diseases in which serum K* is un¬ stable; diverse stimuli trigger attacks, and there are increased K+ fluxes between serum and other cells. Other abnormalities include dilation of sarcoplasmic reticulum, with accumula¬ tion of glycogen, vacuolization of muscle, and decreases in skeletal muscle membrane potentials. De¬ creased calcium-binding and some en¬ zyme activities of sarcoplasmic retic¬ ulum have been reported for three cases of thyrotoxic hypokalemic peri¬ odic paralysis and one sporadic case.46 Other possible derangements of ionic pumping of sodium and potassium or carbohydrate metabolism have long been suspected.7 The present paper describes a black family with hypokalemic periodic pa¬ ralysis, treatment with acetazolamide and other diuretics, and studies to define the action of acetazolamide and the mechanism triggering attacks. (This is the second black family with this disease to be reported; the first was described by Talso et al.s) The chief finding was that, in the provoca¬ tive test (insulin and glucose loading), which lowers serum 1, acetazolamide notably blunted the hypokalemic ef¬ fect.
Table 1.—Clinical Data Patient 1 27, M 22
Age (yr), sex Age at onset, yr
on
Patients
Patient 2 31, M 20
Treatment*
Attacks/yr
Control
Mild Moderate
Control
Rx 2
10
t 52 12 155 105
Severe
Blood pressure,
mm
Hg
140 100
Precipitating factors Exercise Rest
Emotional stress
High-carbohydrate diet Ethyl alcohol Cold Serum concentration Sodium, mM Potassium, mM CO„ mM CPK (normal, 3 to 35 units) Aldosterone, /¿g/24 hr
124 86
Yes Yes No Yes No No Control 136 3.6 26
Yes Yes No No No No Control 134 3.8 28 515
Rx 132 3.4 15
Patient 4 35, M
Patient 3 33, M 12
Control
Rx 1
RxA 12
1Í
M RxM 0
Control
t
Dy RxDy 2
RxA 0
50
10
24
150 100
1_27 93
Control
Rx 132 4.0 23
147 4.8 28 556
112 70
Yes Yes Yes Yes Yes No RxA 150 3.6 21
158 118
138 98
Yes Yes No No No No Control 136 4.6 22 316
RxDy 140 4.3 27
(normal, 2 to 26)
Thyroxine, ^g/100 mi (normal, 3.8
*
to
8.3)
A, Acetazolamide, 250
6.6 mg every six
chlorothiazide, 25 mg, one dose per day. t Patients had chronic mild weakness restricted
These studies, coupled with the known capacity of acetazolamide to produce metabolic acidosis,9 the ef¬ fects of acidosis that reduce K* influx from serum to muscle,1011 and the increased K* entry from serum to muscle during attacks,12·13 suggest the following mechanism for the benefi¬ cial effects of the drug: Attacks are usually associated with greatly increased K> entry from serum to muscle, so that serum K+ drops about 2 mM. Acetazolamide induces a metabolic acidosis, the effect of which is to decrease K+ influx from serum to muscle, thus opposing the abnormality that causes
paralysis.
REPORT OF CASES Four brothers a
were
4.0
hours. M, Methazolamide, 50 to 100
studied, members of
family whose eight siblings included one
affected sister, one unaffected brother, and two unaffected sisters. The father (deceased) reportedly had episodic weak¬ ness; the mother is alive and well with no signs of weakness. Attacks were defined as mild when weakness was noticed by the patient or detectable on examination but not appar-
to one or two
ent to
a
6.8
5.3 mg every
eight hours. Dy, Dyazide: triamterene, 50
mg,
+ hydro-
limbs.
casual observer. Moderate attacks
produced limb or trunk weakness apparent to a casual observer during everyday activ¬ ities, but not severe enough to prevent sitting, standing, or walking. Severe attacks prevented these activities. At no time was respiration impaired. The aver¬ age duration of moderate or severe attacks was one or two days; mild attacks often
lasted weeks or months. The four patients were evaluated for the following (Table 1): complete blood count; erythrocyte sedimentation rate; serum cho¬ lesterol, calcium, and phosphorus; creatine
phosphokinase (CPK); thyroxine as T4; two-hour postprandial blood glucose; VDRL test and electrophoresis; creatinine clearance and urinalysis; chest x-ray films and intravenous pyelogram; electromyo¬ graphy and nerve stimulation. Results of these studies were normal unless noted otherwise. Twenty-four-hour urinary aldosterone level was obtained after seven days of a high sodium chloride diet containing at least 8 gm of sodium per day. Urinary renins were checked each morn¬
ing. Case 1.-Patient 1 was strong and muscular in his youth. At age 22, on entering the Marine Corps, his first attack of generalized weakness occurred after running five miles. The weakness persisted for three weeks. Thereafter, attacks were
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precipitated by
rest
following prolonged
calisthenics. In August 1972, he was a muscular, 27year-old man with excellent strength and normal reflexes. Results of a biceps muscle biopsy were normal except for a few scat¬ tered, small, rounded muscle fibers, stained by Gomori trichrome, which were both type I and type II fibers by histochemical stain¬ ing. In quantitative electromyography of the opposite biceps, the mean action poten¬ tial duration was 11.7 msec (normal 10.4 msec ± 20%). Ulnar motor nerve conduc¬ tion was normal at 62 meters/sec in the wrist-elbow segment; ulnar sensory nerve conduction was also normal at 56 meters/ sec. Blood pressure and attacks of paralysis were both controlled over the subsequent II months by acetazolamide, 250 mg four times a day (Table 1). Case 2.-Patient 2, 31 years old, had weakness of elbow flexors and extensors and hip flexors. Tendon reflexes were diminished but present. Muscle biopsy results were normal except for minimal type II muscle fiber atrophy. Results of electromyography and motor and sensory nerve conduction studies were normal. Oral acetazolamide, 250 mg four times daily, resulted in normal strength, return of reflexes, and virtual freedom from attacks for 12 months (Table 1). Case 3.-Patient 3,33 years old, although =
t • a
+
°
5
or. =
E
Glucose-Insulin
Acetazolamide
•
,
dose
single
o
Moderate Restricted Weakness
Test 2 Before Acetazolamide
mt
Moderate Generalized Weakness
1.8 1.6 1.4 1.2 1.0
1.6 1.4 1.2 m ^ ·| 1.0 rx £ E
+
ol% +"
4.0 3.5 3.0 2.5
¡1 w
0,100 »
50
JS S
i &°
I
< a.
E
u
treatment
t+
Mild Generalized Weakness
o ° o
2.
,
-+++
I 150
_
During Acetazolamide chronic
Mild Restricted (One Limb) Weakness
Test 1 Before Acetazolamide
4.5 4.0 3.5 3.0 2.5
n
Test
+
E°
4.0 3-5 3.0
g
150
8°
loo
E
so
-2
m O
C»
,_
ifE 3 uj
,
co
4.0 3.5
.
O « _l_I_I_I_l_I
0
30
90
I_I_l_I_l_u
150
210
270
330
O «
0
Minutes
muscular and well developed, had minimal weakness so that a push-up was done with difficulty. Tendon reflexes were hypoactive in the arms and absent in the legs. There was an abnormally short mean duration of motor unit potentials (5.4 msec) in the biceps when strength was reduced to just being able to overcome gravity. No spontaneous electrical activity was noted on sampling numerous proximal and distal limb muscles during the attack. Nerve conduction was normal except for a decrease in the amplitude of the evoked muscle action potential. Ten and fifteen days after initiating oral administration of acetazolamide, 250 mg four times daily, right and left renal colic occurred. Some gravel was passed. On examination two weeks later, while still on acetazolamide, serum uric acid was 7.8 and 8.5 mg/100 ml (before acetazolamide ther¬ apy, serum uric acid level had been 5.5 and 5.8 mg/100 ml; normal, 3.4 to 7.8 mg/100 ml); the urinary uric acid value was 700 mg/24 hr (normal, less than 1,000 mg); 24-
90
150
210
270
330
Minutes
Fig 1.—Metabolic studies in patient (case 3) with familial periodic paralysis. Acetazolamide, 500 mg, was administered
triceps
30
intravenously. Patient was tested twice before (A) and once during chronic acetazolamide treatment, five weeks later (B).
urinary calcium value was 85 mg (normal, less than 250 mg); and urinary pH was 5 to 6. Roentgenographic examination for renal calculi showed no abnormality. The episode was attributed to elevated plasma and tissue uric acid due to inhibi¬ tion of uric acid secretion by acetazola¬ mide.11 The gravel was presumably the
hour
radiolucent uric acid. Acetazolamide was discontinued and orally administered methazolamide, 100 mg initially and later 50 mg every eight hours, was substituted because it probably does not block urinary excretion of uric acid." Attacks of paral¬ ysis were then well controlled (Table 1), and no further episodes of renal colic occurred during the subsequent 12 months. Acetazolamide (500 mg in two minutes) was administered intravenously during an induced attack (Fig 1). The course of weak¬ ness and recovery appeared to be unaf¬ fected by this dose. Case 4.-Patient 4 was well developed at 35 years of age and exhibited minimal hip
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flexor weakness and areflexia. Results of a right biceps muscle biopsy were normal except for a few scattered, small, round muscle fibers that were both type I and type II by histochemical stains. Electro¬ myography and nerve conduction tests showed no abnormalities. Serum electrophoresis showed a hyper-/?- and diffuse hyper-y-globulinemia (1.4 and 1.8 gm/100 ml, with a normal of 0.6 to 1.2 and 0.6 to 1.6
gm/100 ml, respectively). Dyazide (triam-
terene, 50 mg, and hydrochlorothiazide, 25
mg), given orally once daily, resulted in normal strength and reflexes, as well as good control of attacks of paralysis and hypertension for nine months, after which time equally good control was obtained with orally administered acetazolamide, 1 gm per day (Table 1). None of the patients received supple¬ mental potassium. METHODS The study included normal individuals and these four patients. Control subjects
Table 2.—Effect of Glucose-Insulin on Serum K+ in Three Patients With Hypokalemic Periodic Paralysis: Alteration of Response by Acetazolamide Before Glucose-Insulin
pH
C02
K+
After Glucose-Insulin
Ch pH P04= Control (n=5) 102.2 3.2 7.42
C02
K+
CI"
23.8 0.9
2.44 0.14
102.4 1.0
2.7 0.2
3.07 0.12
111.0 2.9
3.7j
P04=
*
Mean :SE
7.42 0.01
25.2 1.2
Mean :SE
7.36 0.02
22.6 1.2
4.36 0.13
0.7
0.1 0.01 Acetazolamide Treatment (n=3)f 4.00 105.7 7.33 20.3 3.8t 0.20 2.0 0.03 1.5 ...
Two of the patients were tested twice. t Plasma concentrations of drug ranged from tions ranged from 14/jg/ml to 15/ig/ml. $ One test only. *
healthy, paid volunteers, two men and two women, ages 22 to 25 years. At 8 am, an were
18-gauge scalp vein needle was placed in the cubital vein, and the initial blood samples were drawn. One hour later glucose (1.75 gm/kg, orally as Glucola) and insulin (regular, 20 units intramuscularly) were administered. Blood samples were drawn every half hour for the duration of the experiment and analyzed for pH,
sodium, potassium, chloride, bicarbonate, glucose, and inorganic phosphate. Samples
also drawn every 90 minutes for determination of red blood cell potassium influx. Following the initial control study, each volunteer was placed on acetazo¬ lamide (250 mg four times a day). After one week, the volunteer returned and was admitted to the hospital, and the test was repeated. Procedures were fully explained to the normal volunteers and to the patients, and written consent was ob¬ tained. The physicians in attendance were ready for measures to counter respiratory failure, although, to our knowledge, this has never been reported following glucoseinsulin administration. Serum sodium and potassium levels were determined by flame photometry, and serum chloride and bicarbonate by an auto¬ mated system of chemical analysis. Blood glucose was measured by blood sugar kit, blood pH by blood gas analyzer, and serum phosphate by the Whitehorn modification of Bell-Doisy method.15 Blood thyroxine content was obtained by means of a T4 diagnostic kit; creatine phosphokinase val¬ ue was determined by the Rosalki assay; aldosterone level was obtained by radioimmunoassay. Potassium influx to red cells was determined in triplicate by modifica¬ tion of a method described previously.' Modifications included a reduction in volume of the whole cell suspension to 15 ml and a reduction of potassium 42 to 5 microcuries per millimol K* of external media. The isotope was in an acid solution. were
3fig/ml
to
16/tg/ml. Red
blood cell concentra¬
Serum drug levels of acetazolamide were determined by the method of Maren et al."
Patients were evaluated frequently dur¬ ing the experiment for clinical changes. Electrocardiograms and vital capacities were monitored. Weakness was always associated with a decrease or absence of tendon reflexes in the muscle involved. Weakness was considered mild if gravity could be overcome and the force of resist¬ ance was good or very good, but definitely less than the attack-free state. With moderate weakness, the force of resistance was
weak; with
severe
weakness, gravity
could not be overcome. Attacks were restricted if weakness was only in one limb and were generalized if weakness involved more than one limb. The limb used for obtaining blood samples was not tested.
RESULTS Metabolic Findings in Patients
Before drug (Fig 1, A) the patient was in normal acid-base balance, serum pH 7.41 and C02 28 mM. During the test, while receiving the drug, (Fig 1, B), serum pH was 7.39 and C02 21 mM. During drug treatment, serum K+ was slightly reduced (to 3.6 mM), and blood glucose and serum phos¬ phate were unchanged. The flux stud¬ ies on entry of K* to red cells (before glucose-insulin) showed that acetazo¬ lamide reduced flux about 20%, in agreement with other data on normals and patients with hyperkalemic peri¬ odic paralysis.1·2 Glucose-insulin lowered serum K* 2.0 and 1.8 mM in two tests before the drug (Fig 1, A). In the same test during drug treatment, the K* decre¬ ment was 0.6 mM (Fig 1, B). Table 2 extends the principal find-
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ing of Fig 2 to two other patients, showing again that the effect of glucose-insulin on serum K* is sub¬ stantially lessened by acetazolamide. There is also the suggestion that acetazolamide modifies the fall in serum
P04
=.
The effect of the glucose-insulin test on the influx of K* to red cells was equivocal in the experiments of Fig 1. Before treatment with acetazo¬ lamide (Fig 1, A), one test showed no change in K+ influx, the other a trans¬ ient decrease. During treatment with acetazolamide (Fig 1, B), K* influx lowered but glucose-insulin was caused no further change. (Further data on this point are given in Fig
3.)
Glucose-insulin produced marked weakness in the two control tests (Fig 1, A); this was not altered by intrave¬ nous administration of acetazolamide. After long-term acetazolamide ad¬ ministration, there was much less weakness following glucose-insulin,
although weakness was abolished (Fig 1, B).
not
entirely
The effect of acetazolamide on the blood glucose curves following glu¬ cose-insulin is shown in Fig 2. The drug reduced the glucose level and shortened recovery time in two of the
patients.
Metabolic Findings in Normal Volunteers
The four normal persons developed all the characteristics of chronic carbonic anhydrase inhibition: lower¬ ed serum pH, C02, and K+, and normal Na+ and P04= (Table 3). There was no respiratory acidosis. In these normal subjects, the effect of glucose-insulin on serum K* was slight (Table 3) compared to the patients (Table 2). The fall in serum K+ averaged 0.6 mM before drug and 0.42 mM during treatment. This is not a significant difference, but in two of the four, (Fig 3, top right and bottom right) the drug did appear to reduce the decrement in K* (not shown in the
figure). Long-term administration of aceta¬
zolamide reduced K+ influx into normal red cells (Fig 3), as in the patients (Fig 1). Glucose-insulin in¬ creased K> flux into red cells, and
acetazolamide
opposed this effect (Fig
3).
180
Differences in blood glucose follow¬ ing glucose-insulin, before and after acetazolamide, were small. Acetazo¬ lamide seemed to elicit a higher peak and more rapid fall than observed in the controls (Fig 4). More work is needed to confirm this.
130-
Therapeutic Effect of Acetazolamide in Hypokalemic Periodic Paralysis Relation to Other Drugs Used.—All four patients were much improved by acetazolamide. Only occasional mild attacks were observed or reported. Some mild weakness persisted in case 4 during treatment, but much less than before treatment. Serum HC03- and acetazolamide levels during one year usually showed an acidosis and presence of drug, although these were occasionally less than expected, indicating some failure of compliance (Table 4). The data were not adequate to correlate serum pH and HC03- at any given time with either clinical effects or protection against K> fall in serum. However, during the glucose-insulin tests of Fig 1 and Table 2, there was always some acidosis during acetazolamide treat¬
230-
E
180-
130
180
ment.
The minimum effective dose of acetazolamide for control of this disease cannot be determined preci¬ sely from our data, but it is probably 500 to 1,000 mg daily, in single or divided doses. This is the dosage usually given for glaucoma and yields full inhibition of carbonic anhydrase.9 Methazolamide appears to be effec¬ tive at a lower dose, as in glaucoma. In our view, methazolamide might pres¬ ently be the drug of choice, since it probably will not cause uric acid stones14
(case 3).
The beneficial effect of Dyazide (case 4) is not due to carbonic anhy¬ drase inhibition or to metabolic acido¬ sis. It is likely that the K+-retaining and NaMosing effect of this combina¬ tion is responsible.8 COMMENT
The effects of glucose-insulin, which lower serum K* 2 mM in patients with hypokalemic familial
130-
Minutes
Fig 2.—Blood glucose content in familial periodic paralysis following glucose-insulin (arrows). Solid lines, Before acetazolamide. Dashed lines, During acetazolamide. Top, Case 1. Center, Case 2. Bottom, Case 3.
periodic paralysis,
were taken as a model for attacks of the disease. The effects of acetazolamide were studied in this context. The main finding relevant to the effect of acetazolamide on the disease is that of stabilizing serum K+ against the fall. Since acidosis reduces the
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influx of K+ into muscle (and probably other sites as well),10·11 it is reasonable to assume that acetazolamide works through the induction of acidosis; the acidotic state opposes the tendency of K+ to leave serum for intracellular sites in normals and in patients with this disease.
2.0
1.8 1·6
I
O
1.4
m
er
1.2
+ :
2.0
»
o
J
1.8
I
1.6 1.4 1.2
120
240
360
120
240
360
Minutes
Fig 3.—Potassium influx into red cells taken from normal volunteers after glucoseinsulin (arrows). Solid lines, No drug. Dashed lines, After one week receiving acetazol¬ amide orally. Vertical lines show standard error of mean of four flux measurements. Top left, 22-year-old woman. Top right, 21-year-old man. Bottom left, 23-year-old woman. Bottom right, 25-year-old man. Table 3.—Effect of Glucose-Insulin on Serum and Red Blood Cell K+ in Four Normal Volunteers: Effect of Acetazolamide* After Glucose-Insulin
Before Glucose-Insulin Serum
Serum
RBC
pH
CO,
Na+
7.43
21
138
4.0
7.36
li
140
3.7
pH
P04=
CO,
Control 7.45 22 Acetazolamide Treatment 3.6 91 7.37 15 3.6
99
RBC
Na+
PO.
137
3.4
3.0
99
137
3.3
2.6
92
The potassium decrement in control series (—0.6 mM) is not statistically different from that (—0.4 mM) in the treated. Mean data (mM). t Plasma levels were 8,ag/ml to 18/¡g/ml. *
This mechanism invoking metabolic acidosis appears to fit all the facts at hand, in the present and other studies. Direct action of acetazolamide at the muscle membrane had been hard to visualize, since there is no carbonic anhydrase in muscle and since we have shown that there is no direct effect of the drug on K* exchange in isolated muscle" or in red blood cells in vitro.1 Griggs et al suggested that acidosis might be the key factor.18 To test this, they discontinued acetazolamide and administered NH4C1 to one patient. Unfortunately, the dose was too small, the metabolic acidosis achieved by acetazolamide was actually dissipated
during NH4C1 treatment, and the attacks returned. This critical experi¬ ment remains to be done, but would require some 10 gm or more of NH4C1 per day. Viskoper et al19 found that intrave¬ nously administered NH4C1 (2 gm) improved the electromyogram results of one patient and NaHC03 (1 mEq/ min x 60 min) caused deterioration of the electromyogram results, with a frank paralytic attack.'9 These obser¬ vations are in qualitative agreement with our data and conclusions, but further work remains to be done, including acid-base and K* measure¬ ments
following NH4C1. Furthermore,
acidosis and alkalosis may also have
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effects directly on the disease unre¬ lated to K> movement, as suggested by Viskoper et al's'9 NaHCO:, experi¬ ment, in which paralysis ensued with normal serum K* levels. The argument in favor of the role of metabolic acidosis is supported by the fact that, in a dose that completely in¬ hibits carbonic anhydrase, intrave¬ nously administered acetazolamide (500 mg) has no perceptible effect on an induced attack (Fig 1, A), whereas equivalent or lower serum concentra¬ tion during chronic treatment does ameliorate the symptoms. Viskoper et al19 reported that intravenously ad¬ ministered acetazolamide abolished an attack, but this attack was precipi¬ tated by NaHCO„ which was stopped (with corresponding drop in serum HCOr) when acetazolamide was giv¬ en (Fig 3 of their study). We found, in agreement with Grob et al,2" that glucose-insulin produced only a modest hypokalemic effect in normals. The effect of acetazolamide in this situation is, thus, difficult to observe, and we obtained only a small difference in the K* decrement between control and treated groups. Quantitative considerations of the overall K* flux from serum to muscle as affected by this disease and by acetazolamide have not been made. A model calculation follows: An adult with 30 kg of muscle and a flux rate for K* of 50 millimols/kg/ hr21 moves 1,500 millimols per hour in and out of muscle, from a serum source of 12 millimols (4 mM x 3 liters of serum) or an extracellular pool of 60 millimols (4 mM x 15 liters). In hypo¬ kalemic familial periodic paralysis, the attack reduces serum or extracel¬ lular K* from 4 to 2 mM in about two hours, which implies that the muscle influx increases (from the extracel¬ lular fluid source) 15 millimols per hour, or 1%. Thus, a relatively small change appears to be the pathophysiological basis for the disease. This lends credence to the likelihood that a rela¬ tively small metabolic alteration (ie, slight acidosis) might reverse it. The acidosis, as previously shown for humans with unimpaired respira¬ tion, is metabolic and partially com¬ pensated.22 Serum HCO.r is lowered some 5 mM and pH 0.1 unit. It is
to note that animal data show that an intracellular (in muscle) acidosis results from carbonic anhydrase inhibition.23 Serum K+ in the present study is low normal in both patients and the normal volunteers. We have confirmed our earlier find¬ ing2 that acetazolamide in vivo re¬ duces flux of K> from plasma to red cell. This may also reasonably be ascribed to the metabolic acidosis. However, this flux is so much smaller (about one thirtieth) than that for muscle that it is unlikely that altera¬ tions play a part either in the cause or treatment of the disease. Although acetazolamide may act by its effect on K+ entry to muscle, this leaves unexplained why, during an attack, it is the resting muscle membrane potential that is abnormal, rather than the ratio of K+ between plasma and muscle.7 It would also be of great interest to explore the rela¬ tion of the present findings to Zierler's suggestion that the defect in hypokalemic disease is failure of acti¬ vation of Na* conductance in the sarcolemma.24 Acetazolamide could correct this, if such a change were pH sensitive, either directly or through an effect on K+ entry. Our data following glucose-insulin show that acetazolamide tends to reduce the peak level of blood glucose (Fig 2) and to bring the level back to normal more rapidly than in untreat¬ ed controls (Fig 4). It appeared that the glucose was more rapidly metabol¬ ized or distributed; it is doubtful that the effect of insulin was enhanced, since acidosis causes relative resis¬ tance to insulin.25 We also show some impairment of glucose tolerance in patients with hypokalemic disease (Fig 2 and also case 4, not shown). The significance of these changes in rela¬ tion to the cause or treatment of the disease is not clear. Our clinical findings agree with others 18·19 that acetazolamide is effec¬ tive in the treatment of hypokalemic periodic paralysis, and our idea that acidosis is the mechanism is related to the finding that dichlorphenamide, a carbonic anhydrase inhibitor of dif¬ ferent structure but also capable of inducing acidosis, is effective.26 The relation of these findings to the
important
Minutes 4.—Blood glucose changes in four normal volunteers following glucose-insulin before (solid lines) and after (dashed lines) one week of acetazolamide treatment. Base¬ line glucose level before injection of glucose-insulin was 77 mg/100 ml in untreated and 78 mg/100 ml in treated persons. Data are means for all persons. Standard errors of means are shown at 30 to 90 minutes.
Fig
Table 4.—Drug and Electrolyte Measurements in Long-Term Treatment of Familial Periodic Paralysis Acetazol-
Serum* RBC* K+
amide,
/¿g/ml
pH
CO, 15 25 29 22
3.4 3.4 4.5 4.2
93 120 119
65
7.44 7.42 7.30
23
4.0 4.1 3.9
91 101 99
50
97 120
14 12
Notes (for 1/17 and 11/8)
Patient 1
9/14/72 11/16/72 1/17/73 11/8/73
0 2 4
probably took drug the day he came to the hospital after lapsing at home; thus
Patient
minimal or absent electro¬ lyte effect
Patient 2
9/14/72 11/16/72 1/17/73 11/8/73
7.41 7.40 7.43
28 25
7.31 7.44
21 25
3.6 5.6
23 11/8/73 7.40 expressed in mM.
4.4
18 12 3
4.1
As above for
patient 1
on
these dates
Patient 3
12/1/72 1/17/73 Patient 4 Data
beneficial effect of acetazolamide in
Aw/perkalemic periodic paralysis is not
clear. There are some, but still insuffi¬ cient, data on the induction of attacks following K+ administration or other stimuli in the presence of acetazolam¬ ide.2·3 Since both hydrochlorothiazide (not a carbonic anhydrase inhibitor in the doses used) and acetazolamide appear to control the hyperkalemic form,2" it is probable that both act by the chief pharmacological property they share, kaluresis. Preliminary data in this laboratory suggested that the elevation of serum K> in hyperkal¬ emic paralysis was modified by aceta-
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zolamide,' but more studies are need¬ ed, particularly since the induction of
acidosis should yield the reverse effect. Considering the two diseases as variations of an entity, we propose that the major effect of acetazolamide is to stabilize muscle membranes against abnormal K+ fluxes, but the intimate details of such processes remain to be discovered.
This study was supported by Public Health Service research grants GM 16934 and NS-528114.
This study was carried out in the Clinical Research Center NIH RR-82-12 at the University of Florida, Gainesville.
1. Hoskins B, Jarrell MA, Maren TH: Effects of carbonic anhydrase inhibitors on potassium exchange in human red blood cells. Arch Int Pharmacodyn Ther 209:186-192, 1974. 2. Hoskins B, Maren TH, Vroom FQ, et al: Acetazolamide and potassium flux in red blood cells: Studies in patients with hyperkalemic periodic paralysis. Arch Neurol 31:187-191, 1974. 3. Hoskins B, Vroom FQ, Jarrell MA: Hyperkalemic periodic paralysis: Effects of potassium, exercise, glucose, and acetazolamide on blood chemistry. Arch Neurol, to be published. 4. Takagi A, Schotland DL, DiMauro S, et al: Thyrotoxic periodic paralysis: Function of sarcoplasmic reticulum and muscle glycogen. Neurology 23:1008-1016, 1973. 5. Au K-S, Yeung RTT: Thyrotoxic periodic paralysis: Periodic variation in the muscle calcium pump activity. Arch Neurol 26:543-546, 1972. 6. Ionasescu V, Schochet SS, Powers JM, et al: Hypokalemic periodic paralysis: Low activity of sarcoplasmic reticulum and muscle ribosomes during an induced attack. J Neurol Sci 21:419\x=req-\ 429, 1974. 7. Hofmann WW, Smith RA: Hypokalemic periodic paralysis studies in vitro. Brain 93:445\x=req-\ 4x74, 1970. 8. Talso PJ, Glynn MG, Oester YT, et al: Body composition in hypokalemic familial periodic paralysis. Ann NY Acad Sci 110:993-1008, 1963. 9. Maren TH: Carbonic anhydrase: Chemistry, physiology and inhibition. Physiol Rev 47:595-781,
1967. 10. Scribner BH, Fremont-Smith K, Burnell JM: The effect of acute respiratory acidosis on the internal equilibrium of potassium. J Clin Invest 34:1276-1285, 1955. 11. Keating RE, Weichselbaum TE, Alanis M, et al: The movement of potassium during experimental acidosis and alkalosis in the nephrectomized dog. Surg Gynecol Obstet 96:323-330, 1953. 12. Grob D, Johns RJ, Liljestrand A: Potassium movement in patients with familial periodic paralysis. Am J Med 23:356-375, 1957. 13. Zierler KL, Andres R: Movement of potassium into skeletal muscle during spontaneous attack in family periodic paralysis. J Clin Invest 36:730-737, 1957. 14. Maren TH: Renal carbonic anhydrase and the pharmacology of sulfonamide inhibitors, in Herken H (ed): Handbook of Experimental Pharmacology. New York, Springer-Verlag, 1969, vol 24, pp 195-256. 15. Peters JP, Van Slyke DD: Quantitative Clinical Chemistry: Methods. Baltimore, Williams & Wilkins Co, 1932, vol 2. 16. Maren TH, Ash VT, Bailey EM: Carbonic anhydrase inhibition: II. A method for determination of carbonic anhydrase inhibitors, particularly of Diamox. Bull Johns Hopkins Hosp 95:244\x=req-\ 255, 1954. 17. Jarrell MA, Maren TH: The effect of acetazolamide on the transport of potassium and rubidium into guinea pig diaphragm. Proc Soc Exp Biol Med 146:1119-1121, 1974.
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18. Griggs, RC, Engle WK, Resnick JS: Acetazolamide treatment of hypokalemic periodic paralysis. Ann Intern Med 73:39-48, 1970. 19. Viskoper RJ, Licht A, Fidel J, et al: Acetazolamide treatment in hypokalemic periodic paralysis: A metabolic and electromyographic study. Am J Med Sci 266:119-123, 1973. 20. Grob D, Liljestrand A, Johns RJ: Potassium movement in normal subjects. Am J Med 23:340-355, 1957. 21. Calkins E, Taylor IM, Hastings AB: Potassium exchange in the isolated rat diaphragm: Effect of anoxia and cold. Am J Physiol 177:211\x=req-\ 218, 1954. 22. Birzis L, Carter CH, Maren TH: Effect of acetazolamide on CSF pressure and electrolytes in hydrocephalus. Neurology 8:522-528, 1958. 23. Maren TH, Ellison AC: The effects of acetazolamide and amiloride on tissue electrolytes, with reference to the teratogenesis of carbonic anhydrase inhibition. J Pharmacol Exp Ther 181:212-218, 1972. 24. Zierler KL: Speculations on hypokalemic periodic paralysis. Am J Med Sci 266:131-133, 1973. 25. Mackler B, Lichtenstein H, Guest GM: Effect of ammonium chloride acidosis on action of insulin in dogs. Am J Physiol 166:191-198, 1951. 26. McArdle B: Metabolic and endocrine myopathies, in Walton JN (ed): Disorders of Voluntary Muscle. Boston, Little Brown & Co, 1969, pp 607-638.
