Archlvee of
Arch. Toxicol. 35, 97--106 (1976)
TOXICOLOGY 9 by Springer-Verlag 1976
Treatment of Experimental lmipramine and Desipramine Poisoning in the Rat* A. G. Rauws and M. Oiling Laboratory of Pharmacology, National Institute of Public Health, P.O. Box 1, Bilthoven, The Netherlands
Abstract. The influence of orally administered activated charcoal on organ concentrations of parenteral imipramine and desipramine was investigated. Ancillary distribution experiments indicated that the gastroenteral cycle of these substances might be more important than the enterohepatic cycle. Nevertheless the effectiveness of repeated activated charcoal dosage in lowering antidepressant concentrations in visceral organs is unpredictable. This is interpreted as a consequence of predominant binding of these drugs in the tissues, in contrast to drugs like acetosal and the barbiturates, which are distributed more evenly in the body water. The conclusion is, that activated charcoal has only limited value as an antidotal adsorbent in imipramine or desipramine poisoning. Key words: Imipramine -- Desipramine -- Activated charcoal - Intoxication Enterohepatic cycle -- Gastroenteral cycle.
Zusammenfassung. Im Tiermodell der Imipraminvergiftung wurde der Einflul3 yon Aktivkohle auf Imipraminkonzentrationen in den Organen untersucht. Aus nebenbei durchgef/ihrten Verteilungsexperimenten stellte sich heraus, dab f/ir lmipramin und Desipramin ein gastroenteraler Kreislauf vorlag, der quantitativ wichtiger war als der seit langem bekannte enterohepatische Kreislauf. Wiederholte Dosierung mit Aktivkohle f/ihrt jedoch zu wechselnden Ergebnissen, soweit es die Organkonzentrationen beider Wirkstoffe betrifft. Das Ergebnis wird interpretiert als eine Folge der starken Gewebsbindung von Imipramin und Desipramin im Gegensatz zu Arzneimitteln wie Acetosal und die Barbiturate, die auch in vivo stark an Aktivkohle adsorbiert werden. Die Ergebnisse f/ihren zu der Schlul3folgerung, dal3 Aktivkohle nur beschr/inkt wirksam ist als Antidot bei der Imipramin- und Desipraminvergiftung. Sehliisselwlirter: Imipramin -- Desipramin -- Aktivkohle -- Vergiftung - enterohepatischer K r e i s l a u f - gastroenteraler Kreislauf. * These results were partly communicatedat the Spring Meeting of the Deutsche Pharmakologische GeseUschaft in Mainz, March 1974.
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Poisoning with tricyclic antidepressants both in adults and in children has been increasingly reported in the last years (Steel et al., 1967; C r o c k e r and Morton, 1969; Noble and Matthew, 1969; Goel and Shanks, 1974; Bickel, 1975). Besides conservative therapy central cholinergic agents have been recommended (Slovis et al., 1971; Burks et aL, 1974). Acceleration of elimination by hemodialysis is useless owing to the low p l a s m a levels o f imipramine and analogues. Acidification o f urine increases excretion o f imipramine and desipramine, but in practice this is ineffective because o f the small contribution of urinary excretion to overall elimination of these substances (Sjfqvist et al., 1969; G r a m et al., 1971). F o r c e d diuresis is not always effective and often is contraindicated because o f circulatory disturbances. Based on results o f investigations on the fate of imipramine (Bickel and Weder, 1968; Bickel and Minder, 1970) one might devise another w a y of increasing the elimination rate of imipramine: intercepting the enterohepatic cycle o f imipramine and its active metabolite desipramine by adsorption to activated charcoal in the small intestine. This would mean that activated charcoal should be administered repetitively, independent o f the completion o f the absorption phase o f the original overdose. Preliminary results with rats along this line reported in 1972 (Rauws and Van Noordwijk, 1972, cf. Table 2 in this paper), were to be published when C r a m m e r and Davies (1972) suggested the same approach. However, the results were not quite satisfactory. Activated charcoal lowered the antidepressant load significantly only in the lungs, as was found by analysis o f variance o f the results of all experiments. In the heart there was only a tendency to a lowering o f the antidepressant load. W e now report further investigations designed to explain this and to provide other a p p r o a c h e s to therapy of imipramine poisoning. F o r technical reasons part of these investigations were carried out with desipramine. The use of desipramine was relevant, because the rate o f formation o f desipramine from imipramine in the rat and in man is greater, than the rate o f elimination o f desipramine (Dingell et al., 1964; Bickel and Weder, 1968), and because it is also used in therapy. Parenteral administration is used, because we were interested only in the processes occurring after absorption o f an oral overdose.
Materials and Methods Materials. Imipramine injection solution (Tofranil, 12,5 mg/ml) was used for animal experiments. For use as a standard and for in vitro experiments imipramine hydrochloride was recrystallized from the injection solution (m.p. 171-174 ~ C). Desipramine substance was provided by Ciba-Geigy, Arnhem, The Netherlands. The melting point of the hydrochloride was 211-216 ~ C, that of the picrate 159-163 ~ C. For animal experiments it was dissolved in dilute hydrochloric acid to the same concentration as imipramine. Analysis. Samples of solid or fluid biological material were ground with an equal weight of sand and 0.5 ml of NaOH 10 mole/l, The pH of the resulting homogenate should be 10 or higher. Anhydrous sodium sulphate was added and ground till a dry, freely flowing powder was obtained. This was extracted for 2.5 hrs with 130 ml of light petroleum (b.p. 40--60 ~ C) in a Soxhlet apparatus. After the extraction 2.25 ml of isoamyl alcohol was added and the volume was completed to 150 ml with light petroleum. Of this extract 75 ml was directly extracted into 5 ml of sulphuric acid 3 mole/l. The drug content in the acid extract was estimated according to Wallace and Biggs (1969) yielding the total concentration of imipramine plus desipramine. The second 75 ml portion was agitated twice with 25 ml pH 5.9 phosphate buffer (Dingell et aL, 1964). Most desipramine then was extracted into the buffer. The remaining imipramine was extracted back into sulphuric acid 3 mole/1 and determined in the same way. The difference of both determinations yielded the desipramine concentration. The recovery of the
Treatment of Imipramine and Desipramine Poisoning
99
method in the range investigated was approximately 70%. The lower limit of the method was 2 ,g. The standard deviation of the method was 10%. 2-Hydroxy-imipramine and other hydroxylated metabolites are not determined by this method. In the therapy and desorption experiments imipramine and desipramine were determined together. Binding to Activated Charcoal. 5 ml of pH 7.4 phosphate buffer with 1 mg of activated charcoal was dialysed against 20 ml of phosphate buffer with imipramine or desipramine at 37 ~ C. After 8 hrs equilibrium was attained and the outer antidepressant concentration was determined correcting for noncharcoal binding by a control experiment without activated charcoal. Animal Experiments. Wistar rats, weighing approximately 150--200 g were used. They were obtained from the Centraal Proefdieren-Bedrijf TNO, Zeist, The Netherlands. Unless mentioned otherwise female animals were used. Bile duct canulation was carried out on rats under urethane anesthesia (1 g/kg of a 25% solution, intraperitoneally). The common bile duct was prepared free and canulated with a polyethene canula (0.28 mm i.d., 0.61 mm o.d.). Bile was collected during 4.5 hrs. After 0.5 hr 50 mg/kg of imipramine or desipramine was administered intraperitoneally. In the distribution experiments groups of 5 rats received imipramine or desipramine (50 mg/kg) intraperitoneally. At the predetermined moments groups of 5 animals were sacrificed and dissected. Therapy Experiments. Groups of 5 rats were orally treated with 2 ml of activated charcoal suspension (10% in 1% Tween-20) or control solution (1% Tween-20) 3, 2, 1, and 0 hrs before the beginning of imipramine or desipramine treatment. With intervals of 10 min they then received five intraperitoneal doses of 10 mg/kg of either imipramine or desipramine. 1 and 2 hrs after the beginning of this series of injections they received again 2 ml of charcoal suspension or control solution. 2 hrs after the last gavage they were sacrificed and imipramine and/or desipramine was determined in heart, liver, and lungs. Desorption Experiments. Rats were given imipramine or desipramine (50 mg/kg) orally in aqueous hydrochloric acid (0.1 mol/l) with 1% Tween-20 (control group) or the same solution with 10% (w/v) activated charcoal added (treated group). After 4 hrs they were sacrificed and imipramine and/or desipramine concentrations in liver, lungs, and heart were compared.
Results
Binding to Activated Charcoal in vitro T a b l e 1 s h o w s the results o f the binding experiments. I n t e r p o l a t e d v a l u e s are given to facilitate c o m p a r i s o n o f i m i p r a m i n e with desipramine. I m i p r a m i n e is m o r e strongly b o u n d t h a n desipramine.
Biliary Secretion D e t e r m i n a t i o n o f i m i p r a m i n e o r d e s i p r a m i n e in bile o f f e m a l e rats o b t a i n e d after c a n u l a t i o n o f the c o m m o n bile d u c t and a d m i n i s t r a t i o n o f i m i p r a m i n e or desipram i n e s h o w e d t h a t o n l y a negligible p a r t o f the d o s e was e l i m i n a t e d via the bile (Fig. 1). Significant a d s o r p t i o n o f i m i p r a m i n e o r d e s i p r a m i n e to t u b i n g leading to s p u r i o u s l y low elimination w a s excluded. T h e c o n c l u s i o n is, t h a t the e n t e r o h e p a t i c c i r c u l a t i o n o f u n c h a n g e d i m i p r a m i n e and d e s i p r a m i n e is n o t as i m p o r t a n t as is s o m e t i m e s suggested.
Intestinal and Gastric Distribution A f t e r the finding that bile c o u l d n o t be an i m p o r t a n t s o u r c e o f i m i p r a m i n e or desipramine, the a m o u n t o f these s u b s t a n c e s in the small intestine w a s investigated at different intervals after their i.p. administration. T h e general result was a m o r e o r less c o n s t a n t a m o u n t o f a n t i d e p r e s s a n t in the intestinal wall ( a p p r o x i m a t e l y 250 ~g
100
A . G . Rauws and M. Oiling
Table 1. Binding of imipramine lIP) and desipramine (DMI) to activated charcoal in vitro Concentration of IP or D M I bound and free (~g/ml)"
IP % adsorbed
10 50 100 150
> 99 92 82 62
DMI % adsorbed > 99 90 62 30
Conditions described in methods.
"
D M I in bile ,,ug/mt
% of dose
8G
O8
6C
0.6
4C
Oz,
O2
1st
2nd
3 rd
4 th
hour
Fig. 1. Biliary elimination of desipramine (DMI) after bile duct canulation in female rats (50 mg/kg, n 4, i.p.) DMI in small inlesline, intestinal wall [] )ug intestinal content E3
100 \\\
50
1
3
4
intestinal segment
Fig. 2. Distribution of desipramine (DMI) in the 4 segments of intestinal wall and corresponding contents, 2 hrs after i.p. administration of desipramine, 50 mg/kg, to female rats (mean and s.d.; n = 5; 1: duodenal segment -- 4: ileal segment)
Treatment of Imipramine and Desipramine Poisoning
101
DMI Ng 500
30C
200
100
Fig. 3. Time course of desipramine in gastric tissue (A) and contents (0) after i.p. administration of desipramine, 50 mg/kg (mean _+ s.d., n = 5). Desipramine content of rat stomach (A) and gastric contents (0)
stomach
lungs
faeces
I
liver urine
Fig. 4. Schematic representation of imipramine and desipramine flow and cycles between various organs in rat in all) and a quantity of antidepressant in the intestinal content decreasing with the distance from the pylorus (Fig. 2) and with time in agreement with Bickel and Weder (1968). The stomach, as a source of the imipramine and desipramine in the intestine was therefore investigated next. In contrast to Bickel and Weder (1968) we found considerable and increasing quantifies in the gastric contents (Fig. 3). In intact animals this amount would be absorbed again in the intestine, constituting a gastroenteral cycle (Fig. 4). The quantity of antidepressant in the stomach wall did not change much during 24 hrs, varying only between approximately 50 and 100 ~xg.
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Time
~g/g 150I +
curveafter im4#amlnelI P)
100 9 I lungs 50
* ~
-o g a s t r r c contents liver
i
15C- DMI
~ 5C
10C
gastric Jcontent5 -A lungs liver
1
2
c
2'~ hrs
8
Fig. 5. Time course of imipramine and desipramine concentrations in liver, lungs, and gastric contents after i.p. administration of imipramine, 50 mg/kg, to female rats (average values of 5 animals)
Timec u r v e /ug/g
after
desiprimlne[ DMI)
30C
~
lungs
:oc i\./
I00
i/r~ 0
liver
i
1 2
i
L
i
8
i
_
2L hrs
Fig. 6. Time course of desipramine concentrations in liver, lungs, and gastric contents after i.p. administration of desipramine, 50 mg/kg, to female rats (average values of 5 animals)
Elimination of Imipramine and Desipramine To compare the elimination of imipramine and desipramine the time course of drug concentrations after equal doses of these drugs was followed in liver, lungs, and gastric contents (Figs. 5 and 6). Whereas after imipramine administration the halflives in liver of both imipramine and desipramine are of the order of 5 hrs, desipramine half-life in the liver after desipramine administration is more than 10 hrs. This suggests saturation of the main metabolic pathway, aromatic hydroxylation, at the dose level used: 50 mg/kg. In the latter case there is an increase of desipramine in the lungs and the gastric contents continuing over 24 hrs.
Treatment of Imipramine and Desipramine Poisoning
103
Table 2. Imipramine and/or desipramine concentration ratio treated/control. Activated Charcoal administered before drug Experiment number
A
B
C
D
E
F
Mean
Heart Liver Lungs
0.54 a 0.60 a 0.72 ~
0.90 0.94 0.70 a
0.70 0.85 0.75
0.47 a 0.76 0.74
1.00 1.10 0.84
0.92 1.10 0.66 ~
0.75 0.87 0.73
P < 0.05 (Wilcoxon). Table 3. Imipramine and/or desipramine concentration ratio treated/control. Activated charcoal administered before and after drug Experiment number
G
H
J
Drug
DMI
DMI
IP
Heart Liver Lungs
-0.66 0.66
0.89 1.06 0.95
0.80 a 0.71 a 0.80
a p < 0.05 (Wilcoxon). Table 4. Imipramine and/or desipramine concentration ratio treated/control after oral administration of drug adsorbed to activated charcoal Experiment number
K
L
Drug
IP
DMI
Heart Liver Lungs Brain
0.61 a 0.69 0.84 0.53
0.11 a 0.40 a 0.47 a 0.20 a
a p < 0.05 (Wileoxon).
Therapy Experiments T h e r a p y e x p e r i m e n t s , a n a l o g o u s to t h o s e d e s c r i b e d earlier ( R a u w s and V a n N o o r d w i j k , 1972), b u t n o w with r e p e a t e d a d m i n i s t r a t i o n o f a c t i v a t e d c h a r c o a l after i n t r a p e r i t o n e a l i n j e c t i o n o f i m i p r a m i n e o r d e s i p r a m i n e did n o t yield results substantially better t h a n the earlier o n e s ( T a b l e 3). T h e r e was no r e a s o n to suspect insufficient availability o f a n t i d e p r e s s a n t for a d s o r p t i o n , a n d so o t h e r e x p l a n a t i o n s h a d to be c o n s i d e r e d .
Desorption Experiments R a t s w e r e t r e a t e d orally with either a solution o f i m i p r a m i n e or d e s i p r a m i n e , or with an a c t i v a t e d c h a r c o a l suspension, l o a d e d with i m i p r a m i n e o f d e s i p r a m i n e . A f t e r 4 hrs the a n i m a l s w e r e killed and heart, liver, lungs, a n d b r a i n w e r e a n a l y z e d .
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The results (Table 4) showed that in the case of imipramine most of the antidepressant adsorbed to the charcoal was desorbed in vivo and was distributed in the organs following the usual pattern. In the case of desipramine almost half of the dose of charcoal was desorbed, as judged by organ levels of desipramine. Apparently the uptake into the organs tends to overrule the adsorption capacity of activated charcoal, even if adsorption has taken place before the administration of the drug. Discussion The results of the first series of therapy experiments (Table 2), together with those of the bile canulation experiments, indicated that interruption of the enterohepatic cycle, proposed by us (Rauws and Van Noordwijk, 1972) and advocated independently by Crammer and Davies (1972) was not an effective way of treating imipramine poisoning. This will not only apply to rats but even more to man, who generally musters less intensive enterohepatic cycles than the rat. As an alternative the gastroenteral cycle was investigated. The finding -- theoretically to be expected -- of high concentrations of antidepressant in the gastric contents was in contrast to the results of Bickel and Weder (1968). The cause of this discrepancy may reside in the extraction procedures. Bickel and Weder (1968) used liquid/liquid extraction of gastric contents, whereas in our investigations all kinds of material were extracted according to Maes (1972) as a sodium sulphate powder in a Soxhlet apparatus. The importance of the stomach was stressed meanwhile by Gard et al. (1973), based on the analysis of gastric aspirate. Fr+javille et al. (1967) even based a very drastic therapeutic measure - gastrotomy - on this consideration. Hart et al. (1969) have made an important contribution in this field by their investigation of gastric dialysis of absorbed drugs. A comparison of imipramine and desipramine distribution with time showed that at the dose level used desipramine inhibits its own elimination. Bickel and Weder (1968) found this autoinhibition already after imipramine administration. Desipramine is a noted inhibitor of microsomal drug metabolism (Sulser et aL, 1966; Kakemi et aL, 1971), presumably by occupying the active site too firmly. In intoxications with drug combinations including imipramine or desipramine or in intoxications with high doses of these antidepressants the build-up of a large amount of antidepressant in the gastric contents may be an important fact to consider. The lack of consistency in the results of our later therapy experiments (Table 3) led us to question the effectiveness of activated charcoal in the case of imipramine and desipramine. The results of the experiments with activated charcoal loaded with imipramine and desipramine confirmed our doubts - or ruined our exaggerated expectations - about activated charcoal. About half of the antidepressant was desorbed, in spite of the excess of activated charcoal. In an analogous experiment carried out with thallium and the specific antidote Prussian blue (Rauws, 1974) only about 3% of the thallium dose was desorbed. Comparing our present results with those with thallium/Prussian blue it is clear that activated charcoal has not enough adsorptive capacity. Experiments with other adsorbents - ion exchange resins, clay minerals, molybdenum disulfide and activated charcoal in liquid paraffin -- did not yield better results. Activated charcoal may be very effective in adsorbing barbiturates, acetosal, paracetamol, or chlorpheniramine (Tsuchiya and Levy, 1972; Dordoni et al., 1973;
Treatment of Imipramine and Desipramine Poisoning
105
Picchioni et al., 1974). These drugs generally are distributed over the total b o d y water and exhibit no p r o n o u n c e d tissue binding. It appears, however, that in the case o f imipramine and desipramine the tissues compete successfully with activated charcoal. M o r e o v e r an acidic p H unfavorable for binding m a y influence this competition at the expense o f adsorption to activated charcoal. Similarly the failure o f activated charcoal to lower/3-methyldigoxin p l a s m a levels (Belz, 1974) m a y be due to strong competition b y tissues. The results of Alv~m (1973), although indicating a significant lowering o f the overall bioavailability o f nortriptyline b y activated charcoal, in most instances do not represent a clinically meaningful decrease o f drug concentration in the first 48 hrs after nortriptyline administration. The conclusion o f our investigation is, that the antidotal effect of activated charcoal should not be taken for granted. H o w e v e r strongly a substance m a y be b o u n d to activated charcoal in vitro, only experiments in vivo - in a d y n a m i c system - will produce results affording extrapolation to the clinical situation. W h e n tissue binding of a drug predominates, activated charcoal should be given in massive doses tO shift the binding equilibrium in the desired direction. A better a p p r o a c h might be the development o f an extremely specific adsorbent for tricyclic antidepressants, with an effectiveness c o m p a r a b l e to that o f Prussian blue in the case o f thallium (Heydlauf, 1969). Acknowledgements. Thanks are due to Ciba-Geigy, Arnhem, The Netherlands, for the gift of desipramine-hydrochloride substance and to British Medical Journal for permission to reproduce Table 1 of our communication in 1972. The able laboratory assistance by Messrs P. Besamusca, H. Heinen, and Y. de Jong as well as help in literature research by Miss S. A. Pikaar and Mrs. Th. van der Stegen is gratefully acknowledged.
References Alvfin, G.: Effect of activated charcoal on plasma levels of nortriptyline after single doses in man. Europ. J. clin. Pharmacol. 5, 236-238 (1973) Belz, G. G.: Plasma concentrations of intravenous/3-methyl digoxin with and without oral charcoal. Klin. Wschr. 52, 749--750 (1974) Bickel, M. H.: Poisoning by tricyclic antidepressant drugs. General and pharmacokinetic considerations. Int. J. clin. Pharmacol. 11, 145-176 (1975) Bickel, M. H., Weder, H. J.: The total fate of a drug: kinetics of distribution, excretion and formation of 14 metabolites in rats treated with imipramine. Arch. int. Pharmacodyn. 173, 433--463 (1968) Bickel, M. H., Minder, R.: Metabolism and biliary excretion of the lipophilic drug molecules imipramine and desipramine in the rat. I. Experiments in vivo and with'isolated perfused rat livers. II. Uptake into bile micelles. Biochem. Pharmacol. 19, 2425--2435; 2437--2443 (1970) Burks, J. S., Walker, J. E., Rumack, B. H., Ott, J. E.: Tricyclic antidepressant poisoning: Reversal of coma, choreoathetosis and myoclonus by physostigmine. J. Amer. med. Ass. 230, 1405-1407 (1974) Crammer, J. L., Davies, B. M.: Activated charcoal in tricyclic drug overdoses. Brit. reed. J. 3, 527 (1972) Crocker, J., Morton, B.: Tricyclic (antidepressant) drug toxicity. Clin. Toxicol. 2, 397--402 (1969) Dingell, J. V., Sulser, F., Gillette, J. R.: Species differences in the metabolism of imipramine and desmethylimipramine (DMI). J. Pharmacol. exp. Ther. 143, 14--22 (1964) Dordoni, B., Willson, R. A., Thompson, R. P. H., Williams, R.: Reduction of absorption of paracetamol by activated charcoal and cholestyramine: A possible therapeutic measure. Brit. med. J. 3, 86--87 (1973)
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Fr~javille, J.-P., Nicaise, A.-M., Febay-Peyroute, F.: Intoxication par l'imipramine. Concours med. 89, 8351--8357 (1967) Gard, H., Knapp, D., Walle, T., Gaffney, T., Hanenson, I.: Qualitative and quantitative studies on the disposition of amitriptyline and other tricyelic antidepressant drugs in man as it relates to the management of the overdosed patient. Clin. Toxicol. 6, 571--584 (1973) Goel, K. M., Shanks, R. A.: Amitriptyline and imipramine poisoning in children. Brit. reed. J. 1, 261--263 (1974) Gram, L. F., Kofod, B., Christiansen, J., Rafaelsen, O. J.: Imipramine metabolism: pH-dependent distribution and urinary excretion. Clin. Pharmacol. Ther. 12, 239-244 (1971) Hart, L. G., Guarino, A. M., Schanker, L. S.: Gastric dialysis as a possible antidotal procedure for removal of absorbed drugs. J. Lab. clin. Med. 73, 853-860 (1969) Heydlauf, H.: Ferric cyanoferrate (II): an effective antidote in thallium poisoning. Europ. J. Pharmacol. 6, 340--344 (1969) Kakemi, K., Sezaki, H., Konishi, R., Kimura, T.: Inhibitory mechanisms of imipramine on barbiturate metbolism in rat liver. Chem. Pharm. Bull. 19, 1395--1401 (1971) Maes, R.: Personal communication, 1972 Noble, J., Matthew, H.: Acute poisoning by tricyclic antidepressants: Clinical features and management of 100 patients. Clin. Toxicol. 2, 403--421 (1969) Picchioni, A. L., Chin, L., Laird, H. E.: Activated charcoal preparations. Relative antidotal efficacy. Clin. Toxicol. 7, 97-108 (1974) Rauws, A. G.: Thallium pharmacokinetics and its modification by Prussian Blue. Naunyn-Schmiedeberg's Arch. Pharmacol. 284, 295-306 (1974) Rauws, A. G., Van Noordwijk, J.: Activated charcoal in tricyclic drug overdoses. Brit. med. J. 4, 298 (1972) Sj6qvist, F., Berglund, F., Borg~, O., Hammer, W., Andersson, S., Thorstrand, C.: The pH-dependent excretion of monomethylated tricyclic antidepressants. Clin. Pharmacol. Ther. 10, 826--833 (1969) Slovis, T. L., Ott, J. E., Teitelbaum, D. T., Lipscomb, W.: Physostigmine therapy in acute tricyclic antidepressant poisoning. Clin. Toxicol. 4, 451--459 (1971) Steel, C. M., O'Duffy, J., Brown, S. S.: Clinical effects and treatment of imipramine and amitriptyline poisoning in children. Brit. med. J. 3, 663-667 (1967) Sulser, F., Owens, M. L., Dingell, J. V.: On the mechanism of amphetamine potentiation by desipramine (DMI). Life Sci. 5, 2005-2010 (1966) Tsuchiya, T., Levy, G.: Relationship between effect of activated charcoal on drug absorption in man and its drug adsorption characteristics in vitro. J. pharm. Sci. 61, 586--589 (1972) Wallace, J. E., Biggs, J. D.: Colorimetric determination of imipramine in biologic specimens~ J. forens. Sci. 14, 528-537 (1969)
Received September 2, 1975
Arch. Toxicol. 35, 97--106 (1976)
TOXICOLOGY 9 by Springer-Verlag 1976
Treatment of Experimental lmipramine and Desipramine Poisoning in the Rat* A. G. Rauws and M. Oiling Laboratory of Pharmacology, National Institute of Public Health, P.O. Box 1, Bilthoven, The Netherlands
Abstract. The influence of orally administered activated charcoal on organ concentrations of parenteral imipramine and desipramine was investigated. Ancillary distribution experiments indicated that the gastroenteral cycle of these substances might be more important than the enterohepatic cycle. Nevertheless the effectiveness of repeated activated charcoal dosage in lowering antidepressant concentrations in visceral organs is unpredictable. This is interpreted as a consequence of predominant binding of these drugs in the tissues, in contrast to drugs like acetosal and the barbiturates, which are distributed more evenly in the body water. The conclusion is, that activated charcoal has only limited value as an antidotal adsorbent in imipramine or desipramine poisoning. Key words: Imipramine -- Desipramine -- Activated charcoal - Intoxication Enterohepatic cycle -- Gastroenteral cycle.
Zusammenfassung. Im Tiermodell der Imipraminvergiftung wurde der Einflul3 yon Aktivkohle auf Imipraminkonzentrationen in den Organen untersucht. Aus nebenbei durchgef/ihrten Verteilungsexperimenten stellte sich heraus, dab f/ir lmipramin und Desipramin ein gastroenteraler Kreislauf vorlag, der quantitativ wichtiger war als der seit langem bekannte enterohepatische Kreislauf. Wiederholte Dosierung mit Aktivkohle f/ihrt jedoch zu wechselnden Ergebnissen, soweit es die Organkonzentrationen beider Wirkstoffe betrifft. Das Ergebnis wird interpretiert als eine Folge der starken Gewebsbindung von Imipramin und Desipramin im Gegensatz zu Arzneimitteln wie Acetosal und die Barbiturate, die auch in vivo stark an Aktivkohle adsorbiert werden. Die Ergebnisse f/ihren zu der Schlul3folgerung, dal3 Aktivkohle nur beschr/inkt wirksam ist als Antidot bei der Imipramin- und Desipraminvergiftung. Sehliisselwlirter: Imipramin -- Desipramin -- Aktivkohle -- Vergiftung - enterohepatischer K r e i s l a u f - gastroenteraler Kreislauf. * These results were partly communicatedat the Spring Meeting of the Deutsche Pharmakologische GeseUschaft in Mainz, March 1974.
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Poisoning with tricyclic antidepressants both in adults and in children has been increasingly reported in the last years (Steel et al., 1967; C r o c k e r and Morton, 1969; Noble and Matthew, 1969; Goel and Shanks, 1974; Bickel, 1975). Besides conservative therapy central cholinergic agents have been recommended (Slovis et al., 1971; Burks et aL, 1974). Acceleration of elimination by hemodialysis is useless owing to the low p l a s m a levels o f imipramine and analogues. Acidification o f urine increases excretion o f imipramine and desipramine, but in practice this is ineffective because o f the small contribution of urinary excretion to overall elimination of these substances (Sjfqvist et al., 1969; G r a m et al., 1971). F o r c e d diuresis is not always effective and often is contraindicated because o f circulatory disturbances. Based on results o f investigations on the fate of imipramine (Bickel and Weder, 1968; Bickel and Minder, 1970) one might devise another w a y of increasing the elimination rate of imipramine: intercepting the enterohepatic cycle o f imipramine and its active metabolite desipramine by adsorption to activated charcoal in the small intestine. This would mean that activated charcoal should be administered repetitively, independent o f the completion o f the absorption phase o f the original overdose. Preliminary results with rats along this line reported in 1972 (Rauws and Van Noordwijk, 1972, cf. Table 2 in this paper), were to be published when C r a m m e r and Davies (1972) suggested the same approach. However, the results were not quite satisfactory. Activated charcoal lowered the antidepressant load significantly only in the lungs, as was found by analysis o f variance o f the results of all experiments. In the heart there was only a tendency to a lowering o f the antidepressant load. W e now report further investigations designed to explain this and to provide other a p p r o a c h e s to therapy of imipramine poisoning. F o r technical reasons part of these investigations were carried out with desipramine. The use of desipramine was relevant, because the rate o f formation o f desipramine from imipramine in the rat and in man is greater, than the rate o f elimination o f desipramine (Dingell et al., 1964; Bickel and Weder, 1968), and because it is also used in therapy. Parenteral administration is used, because we were interested only in the processes occurring after absorption o f an oral overdose.
Materials and Methods Materials. Imipramine injection solution (Tofranil, 12,5 mg/ml) was used for animal experiments. For use as a standard and for in vitro experiments imipramine hydrochloride was recrystallized from the injection solution (m.p. 171-174 ~ C). Desipramine substance was provided by Ciba-Geigy, Arnhem, The Netherlands. The melting point of the hydrochloride was 211-216 ~ C, that of the picrate 159-163 ~ C. For animal experiments it was dissolved in dilute hydrochloric acid to the same concentration as imipramine. Analysis. Samples of solid or fluid biological material were ground with an equal weight of sand and 0.5 ml of NaOH 10 mole/l, The pH of the resulting homogenate should be 10 or higher. Anhydrous sodium sulphate was added and ground till a dry, freely flowing powder was obtained. This was extracted for 2.5 hrs with 130 ml of light petroleum (b.p. 40--60 ~ C) in a Soxhlet apparatus. After the extraction 2.25 ml of isoamyl alcohol was added and the volume was completed to 150 ml with light petroleum. Of this extract 75 ml was directly extracted into 5 ml of sulphuric acid 3 mole/l. The drug content in the acid extract was estimated according to Wallace and Biggs (1969) yielding the total concentration of imipramine plus desipramine. The second 75 ml portion was agitated twice with 25 ml pH 5.9 phosphate buffer (Dingell et aL, 1964). Most desipramine then was extracted into the buffer. The remaining imipramine was extracted back into sulphuric acid 3 mole/1 and determined in the same way. The difference of both determinations yielded the desipramine concentration. The recovery of the
Treatment of Imipramine and Desipramine Poisoning
99
method in the range investigated was approximately 70%. The lower limit of the method was 2 ,g. The standard deviation of the method was 10%. 2-Hydroxy-imipramine and other hydroxylated metabolites are not determined by this method. In the therapy and desorption experiments imipramine and desipramine were determined together. Binding to Activated Charcoal. 5 ml of pH 7.4 phosphate buffer with 1 mg of activated charcoal was dialysed against 20 ml of phosphate buffer with imipramine or desipramine at 37 ~ C. After 8 hrs equilibrium was attained and the outer antidepressant concentration was determined correcting for noncharcoal binding by a control experiment without activated charcoal. Animal Experiments. Wistar rats, weighing approximately 150--200 g were used. They were obtained from the Centraal Proefdieren-Bedrijf TNO, Zeist, The Netherlands. Unless mentioned otherwise female animals were used. Bile duct canulation was carried out on rats under urethane anesthesia (1 g/kg of a 25% solution, intraperitoneally). The common bile duct was prepared free and canulated with a polyethene canula (0.28 mm i.d., 0.61 mm o.d.). Bile was collected during 4.5 hrs. After 0.5 hr 50 mg/kg of imipramine or desipramine was administered intraperitoneally. In the distribution experiments groups of 5 rats received imipramine or desipramine (50 mg/kg) intraperitoneally. At the predetermined moments groups of 5 animals were sacrificed and dissected. Therapy Experiments. Groups of 5 rats were orally treated with 2 ml of activated charcoal suspension (10% in 1% Tween-20) or control solution (1% Tween-20) 3, 2, 1, and 0 hrs before the beginning of imipramine or desipramine treatment. With intervals of 10 min they then received five intraperitoneal doses of 10 mg/kg of either imipramine or desipramine. 1 and 2 hrs after the beginning of this series of injections they received again 2 ml of charcoal suspension or control solution. 2 hrs after the last gavage they were sacrificed and imipramine and/or desipramine was determined in heart, liver, and lungs. Desorption Experiments. Rats were given imipramine or desipramine (50 mg/kg) orally in aqueous hydrochloric acid (0.1 mol/l) with 1% Tween-20 (control group) or the same solution with 10% (w/v) activated charcoal added (treated group). After 4 hrs they were sacrificed and imipramine and/or desipramine concentrations in liver, lungs, and heart were compared.
Results
Binding to Activated Charcoal in vitro T a b l e 1 s h o w s the results o f the binding experiments. I n t e r p o l a t e d v a l u e s are given to facilitate c o m p a r i s o n o f i m i p r a m i n e with desipramine. I m i p r a m i n e is m o r e strongly b o u n d t h a n desipramine.
Biliary Secretion D e t e r m i n a t i o n o f i m i p r a m i n e o r d e s i p r a m i n e in bile o f f e m a l e rats o b t a i n e d after c a n u l a t i o n o f the c o m m o n bile d u c t and a d m i n i s t r a t i o n o f i m i p r a m i n e or desipram i n e s h o w e d t h a t o n l y a negligible p a r t o f the d o s e was e l i m i n a t e d via the bile (Fig. 1). Significant a d s o r p t i o n o f i m i p r a m i n e o r d e s i p r a m i n e to t u b i n g leading to s p u r i o u s l y low elimination w a s excluded. T h e c o n c l u s i o n is, t h a t the e n t e r o h e p a t i c c i r c u l a t i o n o f u n c h a n g e d i m i p r a m i n e and d e s i p r a m i n e is n o t as i m p o r t a n t as is s o m e t i m e s suggested.
Intestinal and Gastric Distribution A f t e r the finding that bile c o u l d n o t be an i m p o r t a n t s o u r c e o f i m i p r a m i n e or desipramine, the a m o u n t o f these s u b s t a n c e s in the small intestine w a s investigated at different intervals after their i.p. administration. T h e general result was a m o r e o r less c o n s t a n t a m o u n t o f a n t i d e p r e s s a n t in the intestinal wall ( a p p r o x i m a t e l y 250 ~g
100
A . G . Rauws and M. Oiling
Table 1. Binding of imipramine lIP) and desipramine (DMI) to activated charcoal in vitro Concentration of IP or D M I bound and free (~g/ml)"
IP % adsorbed
10 50 100 150
> 99 92 82 62
DMI % adsorbed > 99 90 62 30
Conditions described in methods.
"
D M I in bile ,,ug/mt
% of dose
8G
O8
6C
0.6
4C
Oz,
O2
1st
2nd
3 rd
4 th
hour
Fig. 1. Biliary elimination of desipramine (DMI) after bile duct canulation in female rats (50 mg/kg, n 4, i.p.) DMI in small inlesline, intestinal wall [] )ug intestinal content E3
100 \\\
50
1
3
4
intestinal segment
Fig. 2. Distribution of desipramine (DMI) in the 4 segments of intestinal wall and corresponding contents, 2 hrs after i.p. administration of desipramine, 50 mg/kg, to female rats (mean and s.d.; n = 5; 1: duodenal segment -- 4: ileal segment)
Treatment of Imipramine and Desipramine Poisoning
101
DMI Ng 500
30C
200
100
Fig. 3. Time course of desipramine in gastric tissue (A) and contents (0) after i.p. administration of desipramine, 50 mg/kg (mean _+ s.d., n = 5). Desipramine content of rat stomach (A) and gastric contents (0)
stomach
lungs
faeces
I
liver urine
Fig. 4. Schematic representation of imipramine and desipramine flow and cycles between various organs in rat in all) and a quantity of antidepressant in the intestinal content decreasing with the distance from the pylorus (Fig. 2) and with time in agreement with Bickel and Weder (1968). The stomach, as a source of the imipramine and desipramine in the intestine was therefore investigated next. In contrast to Bickel and Weder (1968) we found considerable and increasing quantifies in the gastric contents (Fig. 3). In intact animals this amount would be absorbed again in the intestine, constituting a gastroenteral cycle (Fig. 4). The quantity of antidepressant in the stomach wall did not change much during 24 hrs, varying only between approximately 50 and 100 ~xg.
102
A.G. Rauws and M. Olling
Time
~g/g 150I +
curveafter im4#amlnelI P)
100 9 I lungs 50
* ~
-o g a s t r r c contents liver
i
15C- DMI
~ 5C
10C
gastric Jcontent5 -A lungs liver
1
2
c
2'~ hrs
8
Fig. 5. Time course of imipramine and desipramine concentrations in liver, lungs, and gastric contents after i.p. administration of imipramine, 50 mg/kg, to female rats (average values of 5 animals)
Timec u r v e /ug/g
after
desiprimlne[ DMI)
30C
~
lungs
:oc i\./
I00
i/r~ 0
liver
i
1 2
i
L
i
8
i
_
2L hrs
Fig. 6. Time course of desipramine concentrations in liver, lungs, and gastric contents after i.p. administration of desipramine, 50 mg/kg, to female rats (average values of 5 animals)
Elimination of Imipramine and Desipramine To compare the elimination of imipramine and desipramine the time course of drug concentrations after equal doses of these drugs was followed in liver, lungs, and gastric contents (Figs. 5 and 6). Whereas after imipramine administration the halflives in liver of both imipramine and desipramine are of the order of 5 hrs, desipramine half-life in the liver after desipramine administration is more than 10 hrs. This suggests saturation of the main metabolic pathway, aromatic hydroxylation, at the dose level used: 50 mg/kg. In the latter case there is an increase of desipramine in the lungs and the gastric contents continuing over 24 hrs.
Treatment of Imipramine and Desipramine Poisoning
103
Table 2. Imipramine and/or desipramine concentration ratio treated/control. Activated Charcoal administered before drug Experiment number
A
B
C
D
E
F
Mean
Heart Liver Lungs
0.54 a 0.60 a 0.72 ~
0.90 0.94 0.70 a
0.70 0.85 0.75
0.47 a 0.76 0.74
1.00 1.10 0.84
0.92 1.10 0.66 ~
0.75 0.87 0.73
P < 0.05 (Wilcoxon). Table 3. Imipramine and/or desipramine concentration ratio treated/control. Activated charcoal administered before and after drug Experiment number
G
H
J
Drug
DMI
DMI
IP
Heart Liver Lungs
-0.66 0.66
0.89 1.06 0.95
0.80 a 0.71 a 0.80
a p < 0.05 (Wilcoxon). Table 4. Imipramine and/or desipramine concentration ratio treated/control after oral administration of drug adsorbed to activated charcoal Experiment number
K
L
Drug
IP
DMI
Heart Liver Lungs Brain
0.61 a 0.69 0.84 0.53
0.11 a 0.40 a 0.47 a 0.20 a
a p < 0.05 (Wileoxon).
Therapy Experiments T h e r a p y e x p e r i m e n t s , a n a l o g o u s to t h o s e d e s c r i b e d earlier ( R a u w s and V a n N o o r d w i j k , 1972), b u t n o w with r e p e a t e d a d m i n i s t r a t i o n o f a c t i v a t e d c h a r c o a l after i n t r a p e r i t o n e a l i n j e c t i o n o f i m i p r a m i n e o r d e s i p r a m i n e did n o t yield results substantially better t h a n the earlier o n e s ( T a b l e 3). T h e r e was no r e a s o n to suspect insufficient availability o f a n t i d e p r e s s a n t for a d s o r p t i o n , a n d so o t h e r e x p l a n a t i o n s h a d to be c o n s i d e r e d .
Desorption Experiments R a t s w e r e t r e a t e d orally with either a solution o f i m i p r a m i n e or d e s i p r a m i n e , or with an a c t i v a t e d c h a r c o a l suspension, l o a d e d with i m i p r a m i n e o f d e s i p r a m i n e . A f t e r 4 hrs the a n i m a l s w e r e killed and heart, liver, lungs, a n d b r a i n w e r e a n a l y z e d .
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The results (Table 4) showed that in the case of imipramine most of the antidepressant adsorbed to the charcoal was desorbed in vivo and was distributed in the organs following the usual pattern. In the case of desipramine almost half of the dose of charcoal was desorbed, as judged by organ levels of desipramine. Apparently the uptake into the organs tends to overrule the adsorption capacity of activated charcoal, even if adsorption has taken place before the administration of the drug. Discussion The results of the first series of therapy experiments (Table 2), together with those of the bile canulation experiments, indicated that interruption of the enterohepatic cycle, proposed by us (Rauws and Van Noordwijk, 1972) and advocated independently by Crammer and Davies (1972) was not an effective way of treating imipramine poisoning. This will not only apply to rats but even more to man, who generally musters less intensive enterohepatic cycles than the rat. As an alternative the gastroenteral cycle was investigated. The finding -- theoretically to be expected -- of high concentrations of antidepressant in the gastric contents was in contrast to the results of Bickel and Weder (1968). The cause of this discrepancy may reside in the extraction procedures. Bickel and Weder (1968) used liquid/liquid extraction of gastric contents, whereas in our investigations all kinds of material were extracted according to Maes (1972) as a sodium sulphate powder in a Soxhlet apparatus. The importance of the stomach was stressed meanwhile by Gard et al. (1973), based on the analysis of gastric aspirate. Fr+javille et al. (1967) even based a very drastic therapeutic measure - gastrotomy - on this consideration. Hart et al. (1969) have made an important contribution in this field by their investigation of gastric dialysis of absorbed drugs. A comparison of imipramine and desipramine distribution with time showed that at the dose level used desipramine inhibits its own elimination. Bickel and Weder (1968) found this autoinhibition already after imipramine administration. Desipramine is a noted inhibitor of microsomal drug metabolism (Sulser et aL, 1966; Kakemi et aL, 1971), presumably by occupying the active site too firmly. In intoxications with drug combinations including imipramine or desipramine or in intoxications with high doses of these antidepressants the build-up of a large amount of antidepressant in the gastric contents may be an important fact to consider. The lack of consistency in the results of our later therapy experiments (Table 3) led us to question the effectiveness of activated charcoal in the case of imipramine and desipramine. The results of the experiments with activated charcoal loaded with imipramine and desipramine confirmed our doubts - or ruined our exaggerated expectations - about activated charcoal. About half of the antidepressant was desorbed, in spite of the excess of activated charcoal. In an analogous experiment carried out with thallium and the specific antidote Prussian blue (Rauws, 1974) only about 3% of the thallium dose was desorbed. Comparing our present results with those with thallium/Prussian blue it is clear that activated charcoal has not enough adsorptive capacity. Experiments with other adsorbents - ion exchange resins, clay minerals, molybdenum disulfide and activated charcoal in liquid paraffin -- did not yield better results. Activated charcoal may be very effective in adsorbing barbiturates, acetosal, paracetamol, or chlorpheniramine (Tsuchiya and Levy, 1972; Dordoni et al., 1973;
Treatment of Imipramine and Desipramine Poisoning
105
Picchioni et al., 1974). These drugs generally are distributed over the total b o d y water and exhibit no p r o n o u n c e d tissue binding. It appears, however, that in the case o f imipramine and desipramine the tissues compete successfully with activated charcoal. M o r e o v e r an acidic p H unfavorable for binding m a y influence this competition at the expense o f adsorption to activated charcoal. Similarly the failure o f activated charcoal to lower/3-methyldigoxin p l a s m a levels (Belz, 1974) m a y be due to strong competition b y tissues. The results of Alv~m (1973), although indicating a significant lowering o f the overall bioavailability o f nortriptyline b y activated charcoal, in most instances do not represent a clinically meaningful decrease o f drug concentration in the first 48 hrs after nortriptyline administration. The conclusion o f our investigation is, that the antidotal effect of activated charcoal should not be taken for granted. H o w e v e r strongly a substance m a y be b o u n d to activated charcoal in vitro, only experiments in vivo - in a d y n a m i c system - will produce results affording extrapolation to the clinical situation. W h e n tissue binding of a drug predominates, activated charcoal should be given in massive doses tO shift the binding equilibrium in the desired direction. A better a p p r o a c h might be the development o f an extremely specific adsorbent for tricyclic antidepressants, with an effectiveness c o m p a r a b l e to that o f Prussian blue in the case o f thallium (Heydlauf, 1969). Acknowledgements. Thanks are due to Ciba-Geigy, Arnhem, The Netherlands, for the gift of desipramine-hydrochloride substance and to British Medical Journal for permission to reproduce Table 1 of our communication in 1972. The able laboratory assistance by Messrs P. Besamusca, H. Heinen, and Y. de Jong as well as help in literature research by Miss S. A. Pikaar and Mrs. Th. van der Stegen is gratefully acknowledged.
References Alvfin, G.: Effect of activated charcoal on plasma levels of nortriptyline after single doses in man. Europ. J. clin. Pharmacol. 5, 236-238 (1973) Belz, G. G.: Plasma concentrations of intravenous/3-methyl digoxin with and without oral charcoal. Klin. Wschr. 52, 749--750 (1974) Bickel, M. H.: Poisoning by tricyclic antidepressant drugs. General and pharmacokinetic considerations. Int. J. clin. Pharmacol. 11, 145-176 (1975) Bickel, M. H., Weder, H. J.: The total fate of a drug: kinetics of distribution, excretion and formation of 14 metabolites in rats treated with imipramine. Arch. int. Pharmacodyn. 173, 433--463 (1968) Bickel, M. H., Minder, R.: Metabolism and biliary excretion of the lipophilic drug molecules imipramine and desipramine in the rat. I. Experiments in vivo and with'isolated perfused rat livers. II. Uptake into bile micelles. Biochem. Pharmacol. 19, 2425--2435; 2437--2443 (1970) Burks, J. S., Walker, J. E., Rumack, B. H., Ott, J. E.: Tricyclic antidepressant poisoning: Reversal of coma, choreoathetosis and myoclonus by physostigmine. J. Amer. med. Ass. 230, 1405-1407 (1974) Crammer, J. L., Davies, B. M.: Activated charcoal in tricyclic drug overdoses. Brit. reed. J. 3, 527 (1972) Crocker, J., Morton, B.: Tricyclic (antidepressant) drug toxicity. Clin. Toxicol. 2, 397--402 (1969) Dingell, J. V., Sulser, F., Gillette, J. R.: Species differences in the metabolism of imipramine and desmethylimipramine (DMI). J. Pharmacol. exp. Ther. 143, 14--22 (1964) Dordoni, B., Willson, R. A., Thompson, R. P. H., Williams, R.: Reduction of absorption of paracetamol by activated charcoal and cholestyramine: A possible therapeutic measure. Brit. med. J. 3, 86--87 (1973)
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Fr~javille, J.-P., Nicaise, A.-M., Febay-Peyroute, F.: Intoxication par l'imipramine. Concours med. 89, 8351--8357 (1967) Gard, H., Knapp, D., Walle, T., Gaffney, T., Hanenson, I.: Qualitative and quantitative studies on the disposition of amitriptyline and other tricyelic antidepressant drugs in man as it relates to the management of the overdosed patient. Clin. Toxicol. 6, 571--584 (1973) Goel, K. M., Shanks, R. A.: Amitriptyline and imipramine poisoning in children. Brit. reed. J. 1, 261--263 (1974) Gram, L. F., Kofod, B., Christiansen, J., Rafaelsen, O. J.: Imipramine metabolism: pH-dependent distribution and urinary excretion. Clin. Pharmacol. Ther. 12, 239-244 (1971) Hart, L. G., Guarino, A. M., Schanker, L. S.: Gastric dialysis as a possible antidotal procedure for removal of absorbed drugs. J. Lab. clin. Med. 73, 853-860 (1969) Heydlauf, H.: Ferric cyanoferrate (II): an effective antidote in thallium poisoning. Europ. J. Pharmacol. 6, 340--344 (1969) Kakemi, K., Sezaki, H., Konishi, R., Kimura, T.: Inhibitory mechanisms of imipramine on barbiturate metbolism in rat liver. Chem. Pharm. Bull. 19, 1395--1401 (1971) Maes, R.: Personal communication, 1972 Noble, J., Matthew, H.: Acute poisoning by tricyclic antidepressants: Clinical features and management of 100 patients. Clin. Toxicol. 2, 403--421 (1969) Picchioni, A. L., Chin, L., Laird, H. E.: Activated charcoal preparations. Relative antidotal efficacy. Clin. Toxicol. 7, 97-108 (1974) Rauws, A. G.: Thallium pharmacokinetics and its modification by Prussian Blue. Naunyn-Schmiedeberg's Arch. Pharmacol. 284, 295-306 (1974) Rauws, A. G., Van Noordwijk, J.: Activated charcoal in tricyclic drug overdoses. Brit. med. J. 4, 298 (1972) Sj6qvist, F., Berglund, F., Borg~, O., Hammer, W., Andersson, S., Thorstrand, C.: The pH-dependent excretion of monomethylated tricyclic antidepressants. Clin. Pharmacol. Ther. 10, 826--833 (1969) Slovis, T. L., Ott, J. E., Teitelbaum, D. T., Lipscomb, W.: Physostigmine therapy in acute tricyclic antidepressant poisoning. Clin. Toxicol. 4, 451--459 (1971) Steel, C. M., O'Duffy, J., Brown, S. S.: Clinical effects and treatment of imipramine and amitriptyline poisoning in children. Brit. med. J. 3, 663-667 (1967) Sulser, F., Owens, M. L., Dingell, J. V.: On the mechanism of amphetamine potentiation by desipramine (DMI). Life Sci. 5, 2005-2010 (1966) Tsuchiya, T., Levy, G.: Relationship between effect of activated charcoal on drug absorption in man and its drug adsorption characteristics in vitro. J. pharm. Sci. 61, 586--589 (1972) Wallace, J. E., Biggs, J. D.: Colorimetric determination of imipramine in biologic specimens~ J. forens. Sci. 14, 528-537 (1969)
Received September 2, 1975
