Doxylamine/Pyridoxine for Nausea and Vomiting of Pregnancy

The March 20th issue of The New England Journal of Medicine includes an article from the Office of New Drugs of the FDA on a topic The Medical Letter reviewed in its August 5, 2013 issue: the FDA’s approval of Diclegis, a fixed-dose combination of the H1-antihistamine doxylamine and the vitamin B6 analog pyridoxine, for treatment of nausea and vomiting of pregnancy. Both of these drugs were available individually over the counter before the FDA’s approval of this fixed-dose combination. They were available earlier in the US in another fixed-dose combination called Bendectin, which was withdrawn by the manufacturer in 1983 because of multiple lawsuits claiming that it was teratogenic. It continued to be available in Canada as Diclectin.

It is difficult to prove a negative and especially difficult to prove that a widely used drug is not a teratogen, but in the case of doxylamine/pyridoxine, multiple studies and 2 meta-analyses confirmed the safety of this combination during pregnancy. Moreover, the withdrawal of Bendectin from the US market, where it had been used by as many as 40% of pregnant women, was not followed by a reduction in the frequency of birth defects in general or of any specific malformation.

The FDA publication in The New England Journal of Medicine points out that the withdrawal of Bendectin was associated with a doubling of annual hospitalizations in the US for nausea and vomiting of pregnancy. The authors also speculate that some women who took the drug may have reacted to the frightening news stories about its supposed dangers to the fetus by obtaining an abortion.

Hopefully, this unusual sequence of events will have a permanently happy ending, and the many women who suffer from these unpleasant symptoms will always have an effective remedy. But near the end of their article, the FDA authors assured their readers that they will continue to monitor postmarketing data related to Diclegis. Just in case.

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  1. As an otolaryngologist, I had no occasion to use Bendectin, but I recall numerous patients who took it with good results. Glad it’s back (with a new name).

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