TRIMETHOBENZAMIDE

Fetal Risk Summary

Trimethobenzamide is an antiemetic agent. Reproduction studies have been conducted in rats and rabbits and revealed no evidence of teratogenicity (1). An increased incidence of resorptions and stillborn pups were noted in rats (at 20 and 100 mg/kg) and an increased number of resorptions in rabbits (at 100 mg/kg), but these adverse effects occurred in only one or two dams in both species (1).

Trimethobenzamide has been used in pregnancy to treat nausea and vomiting (2,3). No adverse effects in the fetus were observed. In a third study, 193 patients were treated with trimethobenzamide in the 1st trimester (4). The incidences of severe congenital defects at 1 month, 1 year, and 5 years were 2.6%, 2.6%, and 5.8%, respectively. The 5.8% incidence was increased compared with nontreated controls (3.2%) (p<0.05), but other factors, including the use of other antiemetics in some patients, may have contributed to the results. The authors concluded that the risk of congenital malformations with trimethobenzamide was low.

Breast Feeding Summary

No reports describing the use of trimethobenzamide during lactation have been located. The molecular weight (about 425 for the hydrochloride salt) is low enough, however, that excretion into breast milk should be expected. The potential effects of this exposure on a nursing infant are unknown.

References

1. Product information. Tigan. Roberts Pharmaceutical, 2000.
2. Breslow S, Belafsky HA, Shangold JE, Hirsch LM, Stahl MB. Antiemetic effect of trimethobenzamide in pregnant patients. Clin Med 1961;8:2153–5.
3. Winters HS. Antiemetics in nausea and vomiting of pregnancy. Obstet Gynecol 1961;18:753–6.
4. Milkovich L, van den Berg BJ. An evaluation of the teratogenicity of certain antinauseant drugs. Am J Obstet Gynecol 1976;125:244–8.