The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program. The findings may not have been peer reviewed and were not evaluated in accordance with the levels of evidence criteria established by NTP in March 2009. For more information, see the Explanation of Levels of Evidence for Developmental Toxicity. The findings and conclusions for this study should not be construed to represent the views of NTP or the U.S. Government.
Diphenhydramine HCl, a widely used antihistamine, was evaluated for toxic and teratogenic effects in CD-l mice. DPH (0, 80, 160 and 200 mg/kg/day, po) in distilled water was administered in a volume of 0.01 mL per gram of body weight on days 11 through 14 of gestation (day of sperm detection = gestational day 0). A total of 137 sperm-positive females were treated. Females were weighed and observed daily during treatment for clinical signs of toxicity. At sacrifice on gestational day 17, pregnant females (n=27, 29, 24 and 28 in the control through high dose groups, respectively) were weighed and examined for clinical signs of toxicity, gravid uterine weight and uterine contents (i.e., number of implantation sites, live fetuses, dead fetuses and resorptions). All live fetuses were weighed, sexed and examined for external, visceral and skeletal malformations.
Mortality during the dosing period (i.e., gestational day 11 through 14) was 8.6% (3/35) in the high dose group and 0% in all other treatment groups. Dose-related clinical signs during treatment included lethargy, prone posture, weight loss, tremors, convulsions and death. Maternal weight gain during the treatment period exhibited a significant dose-related reduction for dams treated with 80, 160 or 200 mg/kg/day DPH. Absolute maternal weight gain during gestation (i.e., not including gravid uterine weight) was significantly reduced only for dams treated with 160 mg/kg/day. In addition, significant dose-related decreases were observed for maternal body weight on the final day of treatment (i.e., gestational day 14), maternal body weight at sacrifice (i.e., gestational day 17), weight gain during gestation, and gravid uterine weight. A dose-related increase was observed for maternal relative liver weight. Average fetal body weight per litter was significantly below controls for all DPH-treated groups, with both male and female fetuses being affected in a dose-related manner.
Although the overall incidence of affected fetuses (i.e., resorbed, dead and malformed) did not increase significantly across treatment groups, statistically significant dose-related trends toward increased incidence of gross malformations in general, and of cleft palate in particular, were observed. Although the incidence of cleft palate in the present study was higher than the historical control incidence observed in this laboratory, the incidence was not statistically greater than concurrent controls for any individual treatment group. These results confirm the previous observation in this laboratory that diphenhydramine hydrochloride tends to increase the incidence of cleft palate in CD-l mice, but only at dose levels which produce overt signs of fetal and maternal toxicity and which do not significantly increase the incidence of combined malformations or of affected fetuses.