doxylamine / pyridoxine for nausea and vomiting in pregnancy

Last edited 07/2019

A combination of doxylamine and pyridoxine (vitamin B6) is licensed for the treatment of nausea and vomiting in pregnancy (NNVP) when conservative management has not worked. This is the first antiemetic to be licensed in the UK for the management of nausea and vomiting in pregnancy.

  • the combination provides the action of two unrelated compounds
    • doxylamine succinate (an antihistamine) and pyridoxine hydrochloride (vitamin B6) provide anti-nauseant and antiemetic activity
    • doxylamine succinate, an ethanolamine, first-generation antihistamine crosses the blood-brain barrier and exerts an antiemetic action by selectively binding to H1 receptors in the brain
    • pyridoxine hydrochloride, a water-soluble vitamin, is converted to pyridoxal, pyridoxamine, pyridoxal 5'-phosphate and pyridoxamine 5'-phosphate. Although pyridoxal 5'-phosphate is the main active antiemetic metabolite, the other metabolites also contribute to the biological activity
    • mechanism of action of the combination of doxylamine succinate and pyridoxine hydrochloride to treat nausea and vomiting of pregnancy has not been established (1)

  • a clinical trial has demonstrated that the combination of doxylamine and pyridoxine produced small but statistically significant differences in symptoms and well-being compared with placebo (1)

  • common or very common adverse effects include dizziness, drowsiness, dry mouth and fatigue (1)

  • not aware of any high-quality evidence that shows that the combination of doxylamine and pyridoxine is more effective than other antiemetics (1)

Notes (2):

  • rationale for the delayed-release characteristics of this combination is to allow women to take it before bedtime, when symptoms of NVP tend to be minimal, in order to counteract the increased symptoms more commonly experienced in the morning hours
  • doxylamine succinate-pyridoxine hydrochloride delayed release combination is safe and well tolerated by pregnant women when used in the recommended dose of up to 4 tablets daily in treating nausea and vomiting of pregnancy (2)
  • extensive data suggest that doxylamine/pyridoxine is safe for pregnant women to use, and that it is relatively well tolerated. The results of epidemiological studies designed to detect possible teratogenicity show no association with fetal abnormalities (3)