Teratologic Evaluation of lmipramine Hydrochloride in Bonnet (Macaca radiata) and Rhesus Monkeys (Macaca mulatta) ANDREW G. HENDRICKX California P r i m a t e Research Center, University of California, Davis, California 95616
ABSTRACT Imipramine hydrochloride was administered orally twice daily to 18 bonnet and 3 rhesus monkeys between days 23 and 45 of pregnancy for 1-3 or 1&22 days at 1, 2, and 10 times the recommended human dose. No teratologic changes were observed, although signs of maternal toxicity occurred at the high dose level, and the abortion rate was higher than in controls.
Imipramine hydrochloride (Tofranil, Geigy Pharmaceuticals, Ardsley, New York) is prescribed for the relief of symptoms of depression. Safe use of imipramine during human pregnancy and lactation has not been established because of the inconclusive results of animal reproductive studies and clinical reports of the use of this drug (McBride, '72; Morrow, '72; Rachelefsky et al., '72; Bannister et al., '72; Sim, '72; Kuenssberg and Knox, '72; Idanpaan-Heikkila and Saxen, '73). This report presents the results of an experiment conducted in timed pregnant bonnet (Macaca radzata) and rhesus monkeys (Macaca mulatta).
pregnant since importation. Imipramine hydrochloride was administered twice daily as a tablet by stomach intubation acutely (for 1-3 days) or chronically (19-22 days) (table 1). Nineteen of the treated fetuses were delivered by cesarean section at 70 or 100 days of gestation and two pregnancies terminated in abortion. Ten control fetuses for both species were available for comparison. Immediately after delivery, all fetuses were weighed, measured, and photographed. The viscera were removed, weighed, and fixed in 10% formalin, and the skeletons stained with alizarin red S.
MATERIALS AND METHODS
RESULTS AND DISCUSSION
Female bonnet monkeys weighing 3.55.2 kg and rhesus monkeys weighing 5.29.4 kg were housed individually in aluminum cages and maintained in codpliance with the standards of the Federal Animal Welfare Act and Institute for Laboratory Animal Resources (ILAR). Isoniazid, as a prophylactic against tuberculosis, at an approximate dosage of 5 mglkgiday, was incorporated in the diet, Purina Monkey Chow. Menstruation was detected by daily visual examination of vaginal swabs. The females were bred once, for 2 h, usually 2 days before midcycle; the day of mating was designated as day 0 of pregnancy. Pregnancy was confirmed by bimanual palpation of the uterus per rectum. Twentyone pregnant females were used; 19 produced at least one normal offspring, either before receiving imipramine hydrochloride or afterward; two others had not been
The data are summarized in table 1 . No teratogenic effects of imipramine hydrochloride were observed after either the acute or chronic treatments. The incidence of early abortions was higher in the treated group ( 9 % ) than that observed in our breeding colony (3 % ). These results should be regarded as inconclusive, because the only consistency observed in the two abortions was that they occurred during the same period of pregnancy; they appeared unrelated to the dose or time of treatment. The dose levels used in this study were 1, 2, and 10 times the recommended human dosage, and were approximately 5, 40, and 120 times greater on a mg/kg basis than the prescribed human dosage, considering 54 kg the average weight for women in early pregnancy.
TERATOLOGY, 1 I : 219-222.
Received Sept. 20,'74. Accepted Nov. 22, '74. I Supported by NIH grant RR00169.
219
220
ANDREW G . HENDRICKX TABLE 1
Ejj"ects of i m i p r a m i n e h y d r o c h l o r i d e d u r i n g p r e g n a n c y in b o n n e t f i n d r h e s u s m o n k e y s Treatment Treatment group
-
animals
Day(s) of pregnancy
2 2
23-25 26-28
100 100
22-24 19-22
2 1 1
29-31 2345 3145
100 100 100
24-29 19 22
1 1 1 1
23-25 26-28 29-31 25
200 200 200 200
46 40 43 40
1
1
27 29
200 200
53 44
1
25
1000
213
1
27
1000
244
1
29
1000
222
No. of
Dosage (mg/day) (mg,kgldayl
Outcome of offspring
Bonnet monkeys 1
(1 X recommended
human dose)
2 (2 X recommended
human dose)
3 (10 X recommended
human dose)
Both normal One normal; one abortion on day 45 of pregnancy Both normal Normal Normal Normal Normal Normal Abortion on day 40 of pregnancy Normal Normal Normal; moderate maternal toxicity Normal; severe maternal toxicity effects Normal
Rhesirs m o n k e y s 4 (1 X recommended
2 1
26-45 2845
100 100
10-14 19
Both normal Normal
human dose)
No observable clinical signs of maternal toxicity were observed in groups 1, 2, and 4, but were observed in two of the three animals in group 3. Ataxia and grand mallike seizures were exhibited by the animal receiving 244 mglkg several hours after the first of the 2 daily treatments. Within 6 h of the first treatment she went into a coma, but recovered shortly. The toxic symptoms disappeared within 24 h of the last treatment. The animal receiving 213 mg/kg exhibited similar signs of ataxia, but the grand mal-like seizures were much less severe and did not result in coma. Because of the severe toxicity observed in these animals the scheduled 3-day treatment was reduced to 1 day. These dosages exceed the highest tolerated dose level suggested by Wilson ('73). The acute treatments were designed to test the teratogenicity of this drug during the critical periods of limb development which, based on the sensitive periods for thalidomide, fall on days 25-28 of gestation (Hendrickx and Newman, '73). The acute treatment periods also encompass
the time of neural-tube closure. The chronic treatment period encompasses the critical periods of organogenesis including the period of palate closure (days 4 2 4 5 ) . The organs suspected of being malformed in the offspring of women receiving this drug include limbs, brain, spinal cord (closure defects), skeleton, and palate. On the basis of these data it may be concluded that no teratologic changes were induced in bonnet and rhesus monkeys by acute or chronic treatment with imipramine hydrochloride during organogenesis. Wilson ('74), using smaller doses (2-20 mg/kg) throughout organogenesis in 9 rhesus monkeys, also observed no teratogenic effects. In view of these findings in macaque monkeys and the recent evidence compiled by Wilson ('73) on human pregnancies it appears that the teratogenic potential of these drugs in man is low when used at recommended therapeutic doses. Furthermore there is no evidence to support the original view that reduction deformities of the limbs are typically produced by these drugs.
TERATOLOGIC EVALUATION OF IMIPRAMINE
This study further illustrates the importance of nonhuman primates in teratogenicity testing and, in retrospect, emphasizes their advantages. Wilson (‘73) has recommended the use of nonhuman primates for specific purposes, including a third-level test of drugs that are useful during human pregnancy (for example, antidepressants). The overall relation between human and nonhuman primates in phylogenesis and metabolism as well as a similarity in placental structure and circulation indicate that nonhuman primates, especially macaques and baboons, are of special value in teratogenicity testing. LITERATURE CITED Bannister, P., C. Dafoe, E. S. 0. Smith and J. Miller 1972 Possible teratogenicity of tricyclic antidepressant. Lancet, 1 : 838-839.
22 1
Hendrickx, A . G., and L. Newman 1973 Appendicular skeletal and visceral malformations induced by thalidomide in bonnet monkeys. Teratology, 7: 151-159. Idanpaan-Heikkila, J., and L. Saxen 1973 Possible teratogenicity of imipramine/chloropyramine. Lancet, 2: 282. 1972 Kuenssberg, E. V., and J. S. E. Knox Imipramine in pregnancy. Br. Med. J., 29: 292. McBride, W. G . 1972 The teratogenic effects of imipramine. Teratology, 5: 252 (abstract). Morrow, A. W. 1972 Imipramine and congenital abnormalities. N. Z. Med. J., 75: 228-229. Rachelefsky, R. S., J. W. Flynt, A. J. Ebbin and M. GI. Wilson 1972 Possible teratogenicity of tricyclic antidepressant. Lancet, 1 : 838. Sim, M. 1972 Imipramine and pregnancy. Br. Med. J.. 2: 45. Wilson, J. G. 1973 Environment and birth defects. Academic Press, New York. 1974 Teratologic causation in man and its evaluation i n nonhuman primates. In: International Congress Series No. 310. Excerpta Med., Amsterdam, pp. 191-203.
ABSTRACT Imipramine hydrochloride was administered orally twice daily to 18 bonnet and 3 rhesus monkeys between days 23 and 45 of pregnancy for 1-3 or 1&22 days at 1, 2, and 10 times the recommended human dose. No teratologic changes were observed, although signs of maternal toxicity occurred at the high dose level, and the abortion rate was higher than in controls.
Imipramine hydrochloride (Tofranil, Geigy Pharmaceuticals, Ardsley, New York) is prescribed for the relief of symptoms of depression. Safe use of imipramine during human pregnancy and lactation has not been established because of the inconclusive results of animal reproductive studies and clinical reports of the use of this drug (McBride, '72; Morrow, '72; Rachelefsky et al., '72; Bannister et al., '72; Sim, '72; Kuenssberg and Knox, '72; Idanpaan-Heikkila and Saxen, '73). This report presents the results of an experiment conducted in timed pregnant bonnet (Macaca radzata) and rhesus monkeys (Macaca mulatta).
pregnant since importation. Imipramine hydrochloride was administered twice daily as a tablet by stomach intubation acutely (for 1-3 days) or chronically (19-22 days) (table 1). Nineteen of the treated fetuses were delivered by cesarean section at 70 or 100 days of gestation and two pregnancies terminated in abortion. Ten control fetuses for both species were available for comparison. Immediately after delivery, all fetuses were weighed, measured, and photographed. The viscera were removed, weighed, and fixed in 10% formalin, and the skeletons stained with alizarin red S.
MATERIALS AND METHODS
RESULTS AND DISCUSSION
Female bonnet monkeys weighing 3.55.2 kg and rhesus monkeys weighing 5.29.4 kg were housed individually in aluminum cages and maintained in codpliance with the standards of the Federal Animal Welfare Act and Institute for Laboratory Animal Resources (ILAR). Isoniazid, as a prophylactic against tuberculosis, at an approximate dosage of 5 mglkgiday, was incorporated in the diet, Purina Monkey Chow. Menstruation was detected by daily visual examination of vaginal swabs. The females were bred once, for 2 h, usually 2 days before midcycle; the day of mating was designated as day 0 of pregnancy. Pregnancy was confirmed by bimanual palpation of the uterus per rectum. Twentyone pregnant females were used; 19 produced at least one normal offspring, either before receiving imipramine hydrochloride or afterward; two others had not been
The data are summarized in table 1 . No teratogenic effects of imipramine hydrochloride were observed after either the acute or chronic treatments. The incidence of early abortions was higher in the treated group ( 9 % ) than that observed in our breeding colony (3 % ). These results should be regarded as inconclusive, because the only consistency observed in the two abortions was that they occurred during the same period of pregnancy; they appeared unrelated to the dose or time of treatment. The dose levels used in this study were 1, 2, and 10 times the recommended human dosage, and were approximately 5, 40, and 120 times greater on a mg/kg basis than the prescribed human dosage, considering 54 kg the average weight for women in early pregnancy.
TERATOLOGY, 1 I : 219-222.
Received Sept. 20,'74. Accepted Nov. 22, '74. I Supported by NIH grant RR00169.
219
220
ANDREW G . HENDRICKX TABLE 1
Ejj"ects of i m i p r a m i n e h y d r o c h l o r i d e d u r i n g p r e g n a n c y in b o n n e t f i n d r h e s u s m o n k e y s Treatment Treatment group
-
animals
Day(s) of pregnancy
2 2
23-25 26-28
100 100
22-24 19-22
2 1 1
29-31 2345 3145
100 100 100
24-29 19 22
1 1 1 1
23-25 26-28 29-31 25
200 200 200 200
46 40 43 40
1
1
27 29
200 200
53 44
1
25
1000
213
1
27
1000
244
1
29
1000
222
No. of
Dosage (mg/day) (mg,kgldayl
Outcome of offspring
Bonnet monkeys 1
(1 X recommended
human dose)
2 (2 X recommended
human dose)
3 (10 X recommended
human dose)
Both normal One normal; one abortion on day 45 of pregnancy Both normal Normal Normal Normal Normal Normal Abortion on day 40 of pregnancy Normal Normal Normal; moderate maternal toxicity Normal; severe maternal toxicity effects Normal
Rhesirs m o n k e y s 4 (1 X recommended
2 1
26-45 2845
100 100
10-14 19
Both normal Normal
human dose)
No observable clinical signs of maternal toxicity were observed in groups 1, 2, and 4, but were observed in two of the three animals in group 3. Ataxia and grand mallike seizures were exhibited by the animal receiving 244 mglkg several hours after the first of the 2 daily treatments. Within 6 h of the first treatment she went into a coma, but recovered shortly. The toxic symptoms disappeared within 24 h of the last treatment. The animal receiving 213 mg/kg exhibited similar signs of ataxia, but the grand mal-like seizures were much less severe and did not result in coma. Because of the severe toxicity observed in these animals the scheduled 3-day treatment was reduced to 1 day. These dosages exceed the highest tolerated dose level suggested by Wilson ('73). The acute treatments were designed to test the teratogenicity of this drug during the critical periods of limb development which, based on the sensitive periods for thalidomide, fall on days 25-28 of gestation (Hendrickx and Newman, '73). The acute treatment periods also encompass
the time of neural-tube closure. The chronic treatment period encompasses the critical periods of organogenesis including the period of palate closure (days 4 2 4 5 ) . The organs suspected of being malformed in the offspring of women receiving this drug include limbs, brain, spinal cord (closure defects), skeleton, and palate. On the basis of these data it may be concluded that no teratologic changes were induced in bonnet and rhesus monkeys by acute or chronic treatment with imipramine hydrochloride during organogenesis. Wilson ('74), using smaller doses (2-20 mg/kg) throughout organogenesis in 9 rhesus monkeys, also observed no teratogenic effects. In view of these findings in macaque monkeys and the recent evidence compiled by Wilson ('73) on human pregnancies it appears that the teratogenic potential of these drugs in man is low when used at recommended therapeutic doses. Furthermore there is no evidence to support the original view that reduction deformities of the limbs are typically produced by these drugs.
TERATOLOGIC EVALUATION OF IMIPRAMINE
This study further illustrates the importance of nonhuman primates in teratogenicity testing and, in retrospect, emphasizes their advantages. Wilson (‘73) has recommended the use of nonhuman primates for specific purposes, including a third-level test of drugs that are useful during human pregnancy (for example, antidepressants). The overall relation between human and nonhuman primates in phylogenesis and metabolism as well as a similarity in placental structure and circulation indicate that nonhuman primates, especially macaques and baboons, are of special value in teratogenicity testing. LITERATURE CITED Bannister, P., C. Dafoe, E. S. 0. Smith and J. Miller 1972 Possible teratogenicity of tricyclic antidepressant. Lancet, 1 : 838-839.
22 1
Hendrickx, A . G., and L. Newman 1973 Appendicular skeletal and visceral malformations induced by thalidomide in bonnet monkeys. Teratology, 7: 151-159. Idanpaan-Heikkila, J., and L. Saxen 1973 Possible teratogenicity of imipramine/chloropyramine. Lancet, 2: 282. 1972 Kuenssberg, E. V., and J. S. E. Knox Imipramine in pregnancy. Br. Med. J., 29: 292. McBride, W. G . 1972 The teratogenic effects of imipramine. Teratology, 5: 252 (abstract). Morrow, A. W. 1972 Imipramine and congenital abnormalities. N. Z. Med. J., 75: 228-229. Rachelefsky, R. S., J. W. Flynt, A. J. Ebbin and M. GI. Wilson 1972 Possible teratogenicity of tricyclic antidepressant. Lancet, 1 : 838. Sim, M. 1972 Imipramine and pregnancy. Br. Med. J.. 2: 45. Wilson, J. G. 1973 Environment and birth defects. Academic Press, New York. 1974 Teratologic causation in man and its evaluation i n nonhuman primates. In: International Congress Series No. 310. Excerpta Med., Amsterdam, pp. 191-203.
