Acta Pzdiatr Scand 64: 497-504, 1975
POST-MORTEM DISTRIBUTION AND TISSUE CONCENTRATIONS OF DIGOXIN I N INFANTS AND ADULTS K.-E. ANDERSSON,
A. B E R T L E R and G. WETTRELL
From the Departments of Clinical Pharmacology and Paediatrics, University Hospital, Lund, and Department of Clinical Pharmacology, the Medical School, Linkoping, Sweden
ABSTRACT. Andersson, K.-E., Bertler, di. and Wettrell, G. (Departments of Clinical Pharmacology and Paediatrics, University Hospital, Lund, and Department of Clinical Pharmacology, the Medical School, Linkoping, Sweden). Post-mortem distribution and tissue concentrations of digoxin in infants and adults. Acta Paediatr Scand, 64:497, lWS.-By means of 86Rb uptake inhibition assay, the distribution and tissue concentrations of digoxin in various tissues during maintenance therapy were studied post mortem in 12 infants (aged 5 days to 8 months) and 17 adults (aged 49-91 years). The mean maintenance dose for infants was 0.014 mg/kg bw/24 h and for adults, 0.005 mg/kg bw/24 h. The same relative distribution of the glycoside found in infants and in adults was: choroid plexus>ventricular myocardium> kidney >liver >skeletal muscle. Between infants and adults, the mean digoxin concentrations in choroid plexus, kidney, liver, and skeletal muscle did not differ significantly; however, significant differences were found in the glycoside concentrations in ventricular and in atrial myocardium. Both infants and adults showed a difference in the content of the glycoside within the heart, the concentration in ventricular muscle being significantly higher than in atrial. There seemed to be no direct relation between the tissue concentrations of the glycoside (myocardium, skeletal muscle) and the daily maintenance dose (mg/kg bw/24 h). The results suggest that the myocardial binding of digoxin is higher in infants than in adults. KEY WORDS: =Rb method, tissue digoxin concentrations, tissue distribution of digoxin, myocardial binding of digoxin, infants
Clinical experience shows that paediatric patients with congestive heart failure require higher doses of digoxin per unit weight than d o adults (22). Studies using tritiated glycoside (1 1 , 14)have revealed no significant differences in absorption, tissue fixation, o r excretion between infants and adults which could account for this. Based on their findings, Dungan et al. (1 1) suggested that the larger doses of digoxin required for digitalization of infants were accompanied by increased blood levels and increased tissue concentrations of the glycoside. In fact, many investigators found that standard maintenance doses of digoxin to infants produce higher plasma concentrations than those obtained in adults (13, 25, 29, 32). The doses
given to infants (>1 month) are 2-5 times larger on a mg/kg bw basis than those given to adults. None the less, the differences in plasma concentrations are often small (8, 15, 17, 25, 32). However, infants seem t o tolerate higher plasma concentrations of the glycoside than d o adults, and show no signs of toxicity at plasma levels that are definitely toxic in adults (13, 18, 30). Data on the distribution and tissue concentrations of digoxin in paediatric patients are sparse, and the question whether there are differences in the tissue binding of digoxin between infants and adults has not been settled. In order to further investigate the concentrations of digoxin in different tissues during Acta Pzdiatr Scand 64
K . - E . Andersson et a / .
498
Table 1. Clinicti1 dnta on the cididt patients
Pat. no. Sex
Age at death
I 2 3 4
F M M M
66 75 70 73
5
F
49
6 7 8 9
F M F M
79 85 67 85
10
M
84
II 12 13
F F M
91 79 61
14
M
56
15
M
83
16 17
M F
88 68
Autopsy diagnosis Myocardial infarction Myocardial infarction Coronary arteriosclerosis Gastric resection; femoral venous thrombosis and pulmonary embolism Mb Hodgkin. Aortic and mitral valvular stenosis: aortic valve insufficiency Cardiosclerosis Gastric ulcer with bleeding Carcinoma of the breast Myocardial infarction: pulmonary embolism Acute obstruction of the large bowel: pneumonia Generalized atherosclerosis Myocardial infarction Acute appendicitis with peritonitis; pulmonary embolism Aortic valve stenosis and insufficiency Generalized atherosclerosis: myocardial infarction Carcinoma of the lung Pulmonary fibrosis
maintenance therapy, tissue analyses have been performed post rnortem in 29 patients: 12 infants and 17 adults.
Maintenance dosage of digoxin (mg/kg bw 24 h)
Time between diPlasma digoxin intake goxin conand exitus centration (hours) ( ng/ml)
0.003 0.005 0.002
15 24
0.005
12
0.006 0.006 0.003 0.004
10 14
Interval between plasma sampling and death (days)
-
15 -
0.003
6
0.004 0.005 0.006
22 36 6
0.006
2
0.005
18
0.004 0.005 0.005
20 10 17
PATIENTS AND METHODS
given digoxin ( Lanoxin paediatric solution, BurroughsWellcome Ltd, U K ) according to a prevailing oral dose schedule. The daily mean maintenance dose, 0.014 mg/kg bw, was given at 12 h intervals in 2 equal amounts. In no case were signs of digitalis toxicity observed. The time between the last dose of digoxin and exitus averaged 8 h (range 1.5-12 h).
Tissue samples from 29 digoxin-treated patients-I7 adults and 12 infants-were obtained at autopsy. All except 2 neonates (Nos. 1 and 2, Table 2) had been on maintenance treatment with digoxin for more than 5 days because of congestive heart failure. The two neonates received only the initial oral digitalization dose, 0.05 mg digoxinlkg bw/24 h. Table 1 gives the clinical data on the adult patients whose mean age was 74 years (range 49-91). The mean maintenance dose of digoxin (Lanacnst, AB Draco, Sweden). 0.005 mg/kg bw/24 h. was given in one daily dose. N o patient showed clinical or electrocardiographic signs of digitalis toxicity before or at the time of exiius. The time between digoxin intake and death averaged 15 h , ranging from 2 to 36 h . Table 2 summarizes the clinical data on the paediatric patients whose mean age was 60 days (range 5 days to 8 months). All had serious cardiac malformations. Their clinical diagnoses were mostly based on data obtained at cardiac catheterization and angiocardiography, and were verified at the post-mortem examination. The infants were
Tissuc~digoxin nssciy Specimens were taken from the following tissues within 36 h after death: heart (atrium and ventricle), kidney (mainly cortex), liver, skeletal muscle, brain, choroid plexus, and subcutaneous fat (in adults only). Representative samples of adequate size from areas macroscopically apparently normal could easily be obtained from the different tissues. Skeletal muscle specimens were taken from the iliopsoas muscle; samples from brain (cerebral hemisphere) contained both grey and white matter. The digoxin content in the tissue samples was analysed by means of a modified 86Rbuptake inhibition assay ( 5 ) . After gentle blotting on filter paper, each sample was weighed and, after addition of 10 ml 0.9% saline, homogenized with an Ultra-Turrax homogenizer for 2-4 min in an ice bath. Five ml of the homogenate was extracted with 10 ml dichloromethane. After centrifugation, the dichloromethane phase was transferred to new tubes, and the homogenate was similarly extracted for a second time. From the first extract, samples of various volumes (depending on the concentration of digoxin in the tissue); and from the second, 4 ml samples
Pniienis
A d a P e d i a t r S c a n d 64
Tissue concentrations of digoxin
499
Table 2. Clinical datii on the infants
Pat. no. Sex
I
F
5d
2
M
5d
3 4
M M
I? d I2 d
5
M
13 d
6
F
I7 d
7
F
Im
8
F
2m
9 .M F
3m 3.5 m
11
F
4.5 m
I2
F
8m
10
Maintenance dosage of digoxin img/kg bw/24 h )
Age at death daysid) months (m) Autopsy diagnosis Hypoplastic right ventricle; pulmonary valve atresia: patent ductus arteriosus Transposition of the great arteries: functional single ventricle: coarctation of the aorta: atrioseptal defect: patent ductus arteriosus Interrupted aortic arch Transposition of the great arteries: coarctation of the aorta: atrioventricular defects: tricuspid atresia: patent ductus arteriosus Transposition of the great arteries: preductal coarctation of the aorta: patent ductus arteriosus Transposition of the great arteries: hypoplastic left ventricle: interrupted aortic arch Pulmonary valve atresia: ventricular and atrioseptal defects; patent ductus arteriosus: mitral atresia Preductal coarctation of the aorta; ventricular septa1 defect Mb Down; atrioseptal defect Cardiomegaly; multiple congenital skeletal and muscular defects Common AV-canal: hypoplastic left ventricle Mb Down: common AV-canal: hydronephrosis
Time between digoxin intake and exitus (hours)
Plasma digoxin concentration (nglml)
*
8
-
*
9
-
Interval between plasma sampling and death (days)
1.6
0.01 1 0.013
1.5 I2
-
0.01 1
12
-
0.012
9
I .6
0.012
7
1 .5
0.020
7
1.9
0.016 0.015
12 8
0.017
4
1.2
0.013
I2
2.3
1.6 -
*, not on maintenance therapy, see text. were taken and evaporated to dryness in a fume cupboard. The samples were then handled as described for plasma digoxin mRb assay ( 5 ) . Each tissue sample was analysed on 2-4 occasions. The means of these values are given. T o test the method, heart and skeletal muscle from nondigitalized patients were a y l y s e d . No inhibition of the ffiRbuptake in erythrocytes was produced by extracts from these tissues. In experiments where known amounts of digoxin were added to homogenized skeletal muscle, a recovery of 93.6f3.5% was obtained. In some of the adult and paediatric patients, plasma digoxin concentrations during maintenance therapy had been analysed by means of radioimmunoassay. A commercially available digoxin kit (Schwarz/Mann) was used. These determinations were performed 1-2 1 days before exitus. In no case were changes in the maintenance therapy undertaken. Ccilcul~ition,~ Conventional statistical methods were used. Statistical significance of the difference between two sample means was evaluated by Student's t-test. The same distribution was used to test whether the correlation coefficient differed from zero.
RESULTS Tables 3 and 4 give the digoxin content (ng/g tissue, wet weight) in the various tissues from adults and infants. Both age groups show the same relative distribution of the glycoside (Fig. 1). The highest digoxin concentrations were found in the choroid plexus (infants: 287 ng/g; adults 221 ng/g, mean values). Somewhat lower levels were demonstrated in ventricular (245 and 133 ng/g, respectively) and atrial (165 and 65 ng/g, respectively) myocardium, kidney (167 and 128 ng/g,'respectively),and liver (82 and 72 ng/g, respectively). Low concentrations of the glycoside were found in skeletal muscle ( 3 1 and 30 ng/g, respectively), brain (30 and 32 ng/g. respectively), and subcutaneous fat (10 ng/g; analysed only in adults). The mean digoxin concentrations in choroid plexus, kidney, liver, Acta Pediatr Scand 64
500
K.-E. Andersson et nl.
Table 3. Tissue concentrations of digoxin (nglg wet tissue, meun kstcindrrrd error of mean, S.E.M.) in adults Pat. no.
Choroid plexus
I 2 3 4 5 6 7 8 9 10 II 12 13 14
242 233 I43 72 373 224 235 313 209 340 145 205 228 408
15
105
16 17
145 141
M e a n t S. E. M. 221+23
Brain 30 4 74 3 68 17
5 41 60 21 45 55 3 37 34 II 41 32k6
Ventricular Atrial myocardium myocardium Kidney Ill 87 76 I67 161 I69 131 224 50 296 121 21 1 80 62 84
27 78 50 37 72 81 51 112 27 129 46 73 -
91 I44
-
85 74 56 83 189 253 71 213 54 154 I I3 186 -
-
-
-
-
133216
65+9
skeletal muscle, and brain did not differ significantly between infants and adults. However, significant differences were found between theglycoside concentrations in ventricular @
POST-MORTEM DISTRIBUTION AND TISSUE CONCENTRATIONS OF DIGOXIN I N INFANTS AND ADULTS K.-E. ANDERSSON,
A. B E R T L E R and G. WETTRELL
From the Departments of Clinical Pharmacology and Paediatrics, University Hospital, Lund, and Department of Clinical Pharmacology, the Medical School, Linkoping, Sweden
ABSTRACT. Andersson, K.-E., Bertler, di. and Wettrell, G. (Departments of Clinical Pharmacology and Paediatrics, University Hospital, Lund, and Department of Clinical Pharmacology, the Medical School, Linkoping, Sweden). Post-mortem distribution and tissue concentrations of digoxin in infants and adults. Acta Paediatr Scand, 64:497, lWS.-By means of 86Rb uptake inhibition assay, the distribution and tissue concentrations of digoxin in various tissues during maintenance therapy were studied post mortem in 12 infants (aged 5 days to 8 months) and 17 adults (aged 49-91 years). The mean maintenance dose for infants was 0.014 mg/kg bw/24 h and for adults, 0.005 mg/kg bw/24 h. The same relative distribution of the glycoside found in infants and in adults was: choroid plexus>ventricular myocardium> kidney >liver >skeletal muscle. Between infants and adults, the mean digoxin concentrations in choroid plexus, kidney, liver, and skeletal muscle did not differ significantly; however, significant differences were found in the glycoside concentrations in ventricular and in atrial myocardium. Both infants and adults showed a difference in the content of the glycoside within the heart, the concentration in ventricular muscle being significantly higher than in atrial. There seemed to be no direct relation between the tissue concentrations of the glycoside (myocardium, skeletal muscle) and the daily maintenance dose (mg/kg bw/24 h). The results suggest that the myocardial binding of digoxin is higher in infants than in adults. KEY WORDS: =Rb method, tissue digoxin concentrations, tissue distribution of digoxin, myocardial binding of digoxin, infants
Clinical experience shows that paediatric patients with congestive heart failure require higher doses of digoxin per unit weight than d o adults (22). Studies using tritiated glycoside (1 1 , 14)have revealed no significant differences in absorption, tissue fixation, o r excretion between infants and adults which could account for this. Based on their findings, Dungan et al. (1 1) suggested that the larger doses of digoxin required for digitalization of infants were accompanied by increased blood levels and increased tissue concentrations of the glycoside. In fact, many investigators found that standard maintenance doses of digoxin to infants produce higher plasma concentrations than those obtained in adults (13, 25, 29, 32). The doses
given to infants (>1 month) are 2-5 times larger on a mg/kg bw basis than those given to adults. None the less, the differences in plasma concentrations are often small (8, 15, 17, 25, 32). However, infants seem t o tolerate higher plasma concentrations of the glycoside than d o adults, and show no signs of toxicity at plasma levels that are definitely toxic in adults (13, 18, 30). Data on the distribution and tissue concentrations of digoxin in paediatric patients are sparse, and the question whether there are differences in the tissue binding of digoxin between infants and adults has not been settled. In order to further investigate the concentrations of digoxin in different tissues during Acta Pzdiatr Scand 64
K . - E . Andersson et a / .
498
Table 1. Clinicti1 dnta on the cididt patients
Pat. no. Sex
Age at death
I 2 3 4
F M M M
66 75 70 73
5
F
49
6 7 8 9
F M F M
79 85 67 85
10
M
84
II 12 13
F F M
91 79 61
14
M
56
15
M
83
16 17
M F
88 68
Autopsy diagnosis Myocardial infarction Myocardial infarction Coronary arteriosclerosis Gastric resection; femoral venous thrombosis and pulmonary embolism Mb Hodgkin. Aortic and mitral valvular stenosis: aortic valve insufficiency Cardiosclerosis Gastric ulcer with bleeding Carcinoma of the breast Myocardial infarction: pulmonary embolism Acute obstruction of the large bowel: pneumonia Generalized atherosclerosis Myocardial infarction Acute appendicitis with peritonitis; pulmonary embolism Aortic valve stenosis and insufficiency Generalized atherosclerosis: myocardial infarction Carcinoma of the lung Pulmonary fibrosis
maintenance therapy, tissue analyses have been performed post rnortem in 29 patients: 12 infants and 17 adults.
Maintenance dosage of digoxin (mg/kg bw 24 h)
Time between diPlasma digoxin intake goxin conand exitus centration (hours) ( ng/ml)
0.003 0.005 0.002
15 24
0.005
12
0.006 0.006 0.003 0.004
10 14
Interval between plasma sampling and death (days)
-
15 -
0.003
6
0.004 0.005 0.006
22 36 6
0.006
2
0.005
18
0.004 0.005 0.005
20 10 17
PATIENTS AND METHODS
given digoxin ( Lanoxin paediatric solution, BurroughsWellcome Ltd, U K ) according to a prevailing oral dose schedule. The daily mean maintenance dose, 0.014 mg/kg bw, was given at 12 h intervals in 2 equal amounts. In no case were signs of digitalis toxicity observed. The time between the last dose of digoxin and exitus averaged 8 h (range 1.5-12 h).
Tissue samples from 29 digoxin-treated patients-I7 adults and 12 infants-were obtained at autopsy. All except 2 neonates (Nos. 1 and 2, Table 2) had been on maintenance treatment with digoxin for more than 5 days because of congestive heart failure. The two neonates received only the initial oral digitalization dose, 0.05 mg digoxinlkg bw/24 h. Table 1 gives the clinical data on the adult patients whose mean age was 74 years (range 49-91). The mean maintenance dose of digoxin (Lanacnst, AB Draco, Sweden). 0.005 mg/kg bw/24 h. was given in one daily dose. N o patient showed clinical or electrocardiographic signs of digitalis toxicity before or at the time of exiius. The time between digoxin intake and death averaged 15 h , ranging from 2 to 36 h . Table 2 summarizes the clinical data on the paediatric patients whose mean age was 60 days (range 5 days to 8 months). All had serious cardiac malformations. Their clinical diagnoses were mostly based on data obtained at cardiac catheterization and angiocardiography, and were verified at the post-mortem examination. The infants were
Tissuc~digoxin nssciy Specimens were taken from the following tissues within 36 h after death: heart (atrium and ventricle), kidney (mainly cortex), liver, skeletal muscle, brain, choroid plexus, and subcutaneous fat (in adults only). Representative samples of adequate size from areas macroscopically apparently normal could easily be obtained from the different tissues. Skeletal muscle specimens were taken from the iliopsoas muscle; samples from brain (cerebral hemisphere) contained both grey and white matter. The digoxin content in the tissue samples was analysed by means of a modified 86Rbuptake inhibition assay ( 5 ) . After gentle blotting on filter paper, each sample was weighed and, after addition of 10 ml 0.9% saline, homogenized with an Ultra-Turrax homogenizer for 2-4 min in an ice bath. Five ml of the homogenate was extracted with 10 ml dichloromethane. After centrifugation, the dichloromethane phase was transferred to new tubes, and the homogenate was similarly extracted for a second time. From the first extract, samples of various volumes (depending on the concentration of digoxin in the tissue); and from the second, 4 ml samples
Pniienis
A d a P e d i a t r S c a n d 64
Tissue concentrations of digoxin
499
Table 2. Clinical datii on the infants
Pat. no. Sex
I
F
5d
2
M
5d
3 4
M M
I? d I2 d
5
M
13 d
6
F
I7 d
7
F
Im
8
F
2m
9 .M F
3m 3.5 m
11
F
4.5 m
I2
F
8m
10
Maintenance dosage of digoxin img/kg bw/24 h )
Age at death daysid) months (m) Autopsy diagnosis Hypoplastic right ventricle; pulmonary valve atresia: patent ductus arteriosus Transposition of the great arteries: functional single ventricle: coarctation of the aorta: atrioseptal defect: patent ductus arteriosus Interrupted aortic arch Transposition of the great arteries: coarctation of the aorta: atrioventricular defects: tricuspid atresia: patent ductus arteriosus Transposition of the great arteries: preductal coarctation of the aorta: patent ductus arteriosus Transposition of the great arteries: hypoplastic left ventricle: interrupted aortic arch Pulmonary valve atresia: ventricular and atrioseptal defects; patent ductus arteriosus: mitral atresia Preductal coarctation of the aorta; ventricular septa1 defect Mb Down; atrioseptal defect Cardiomegaly; multiple congenital skeletal and muscular defects Common AV-canal: hypoplastic left ventricle Mb Down: common AV-canal: hydronephrosis
Time between digoxin intake and exitus (hours)
Plasma digoxin concentration (nglml)
*
8
-
*
9
-
Interval between plasma sampling and death (days)
1.6
0.01 1 0.013
1.5 I2
-
0.01 1
12
-
0.012
9
I .6
0.012
7
1 .5
0.020
7
1.9
0.016 0.015
12 8
0.017
4
1.2
0.013
I2
2.3
1.6 -
*, not on maintenance therapy, see text. were taken and evaporated to dryness in a fume cupboard. The samples were then handled as described for plasma digoxin mRb assay ( 5 ) . Each tissue sample was analysed on 2-4 occasions. The means of these values are given. T o test the method, heart and skeletal muscle from nondigitalized patients were a y l y s e d . No inhibition of the ffiRbuptake in erythrocytes was produced by extracts from these tissues. In experiments where known amounts of digoxin were added to homogenized skeletal muscle, a recovery of 93.6f3.5% was obtained. In some of the adult and paediatric patients, plasma digoxin concentrations during maintenance therapy had been analysed by means of radioimmunoassay. A commercially available digoxin kit (Schwarz/Mann) was used. These determinations were performed 1-2 1 days before exitus. In no case were changes in the maintenance therapy undertaken. Ccilcul~ition,~ Conventional statistical methods were used. Statistical significance of the difference between two sample means was evaluated by Student's t-test. The same distribution was used to test whether the correlation coefficient differed from zero.
RESULTS Tables 3 and 4 give the digoxin content (ng/g tissue, wet weight) in the various tissues from adults and infants. Both age groups show the same relative distribution of the glycoside (Fig. 1). The highest digoxin concentrations were found in the choroid plexus (infants: 287 ng/g; adults 221 ng/g, mean values). Somewhat lower levels were demonstrated in ventricular (245 and 133 ng/g, respectively) and atrial (165 and 65 ng/g, respectively) myocardium, kidney (167 and 128 ng/g,'respectively),and liver (82 and 72 ng/g, respectively). Low concentrations of the glycoside were found in skeletal muscle ( 3 1 and 30 ng/g, respectively), brain (30 and 32 ng/g. respectively), and subcutaneous fat (10 ng/g; analysed only in adults). The mean digoxin concentrations in choroid plexus, kidney, liver, Acta Pediatr Scand 64
500
K.-E. Andersson et nl.
Table 3. Tissue concentrations of digoxin (nglg wet tissue, meun kstcindrrrd error of mean, S.E.M.) in adults Pat. no.
Choroid plexus
I 2 3 4 5 6 7 8 9 10 II 12 13 14
242 233 I43 72 373 224 235 313 209 340 145 205 228 408
15
105
16 17
145 141
M e a n t S. E. M. 221+23
Brain 30 4 74 3 68 17
5 41 60 21 45 55 3 37 34 II 41 32k6
Ventricular Atrial myocardium myocardium Kidney Ill 87 76 I67 161 I69 131 224 50 296 121 21 1 80 62 84
27 78 50 37 72 81 51 112 27 129 46 73 -
91 I44
-
85 74 56 83 189 253 71 213 54 154 I I3 186 -
-
-
-
-
133216
65+9
skeletal muscle, and brain did not differ significantly between infants and adults. However, significant differences were found between theglycoside concentrations in ventricular @
