Pyridoxine/doxylamine, sold under the brand name Diclectin among others, is a combination of pyridoxine hydrochloride (vitamin B6) and doxylamine succinate. It is generally used for nausea and vomiting of pregnancy (morning sickness); even though its efficacy has not been proven and subsequent research has led to the removal of recommendations in medical journals.
Medical uses The combination of pyridoxine, commonly referred to as vitamin B6 and doxylamine may be effective for the management of nausea and vomiting of pregnancy, but it is only recommended for use in a small number of cases after lifestyle, diet and vitamin B6. A 2018 review found the benefit was small. Doxylamine and pyridoxine are pregnancy compatible drugs, consistent with FDA's safety assessment of the combination product. They have been categorized by the FDA as a category A drug (no evidence of risk to the fetus). This letter classification system for risk in pregnancy is no longer being utilized and was phased out by the FDA beginning in 2008.
Medical organizations' position The American Congress of Obstetricians and Gynecologists (ACOG) states "Safe and effective treatments are available for more severe cases, and mild cases of nausea and vomiting of pregnancy may be resolved with lifestyle and dietary changes." The American Academy of Family Physicians recommends, "Initial treatment is conservative and includes dietary changes, emotional support, and vitamin B6 supplementation." This treatment has an evidence rating of Grade A ("consistent, good-quality patient-oriented evidence") while the addition of prescribing doxylamine is rated Grade C ("consensus, disease-oriented evidence, usual practice, expert opinion, or case series").
Canadian Family Physician issued a correction stating previous articles which stated Diclectin should be used as a first line therapy were incorrect, based upon undisclosed conflicts of interest with the manufacturer, and not peer-reviewed studies:Recommendations in 2 articles published in Canadian Family Physician, "Nausea and vomiting of pregnancy. Evidence-based treatment algorithm" and "Treatment of nausea and vomiting in pregnancy. An updated algorithm," have subsequently come under critical scrutiny. These articles were not subjected to standard peer review, and Canadian Family Physician acknowledges that upon closer inspection these articles did not provide satisfactory evidence that would have justified the recommendation of doxylamine-pyridoxine as a sole first-line treatment for nausea and vomiting in pregnancy (NVP). More recent Canadian NVP guidelines have been published; however, a subsequent re-analysis questions the conclusions of 1 of the studies cited in these guidelines to justify doxylamine-pyridoxine as a recommended first-line treatment for NVP. Additionally, for the articles in Canadian Family Physician there was an undisclosed conflict of interest with Duchesnay, the manufacturer of Diclectin, the combination of doxylamine-pyridoxine. Canadian Family Physician encourages readers to interpret previously published NVP recommendations with caution. Readers are also referred to the commentary "Motherisk and Canadian Family Physician" in the January 2017 issue of Canadian Family Physician.[Ed: bolding to help summarize information, note please follow link to article to see the footnotes from this article]
Adverse effects Pyridoxine, vitamin B6, is a water-soluble vitamin and is generally recognized as having no adverse effects. After diet changes, it alone is recommended as the secondary treatment plan. The most commonly reported adverse reaction of doxylamine is drowsiness. Other adverse drug reactions associated with doxylamine succinate may include: vertigo, nervousness, epigastric pain, headache, palpitation, diarrhea, disorientation, irritability, convulsions, urinary retention or insomnia. It is not recommended to take doxylamine with other medications of the same class, medications that act on the central nervous system (CNS) or with alcohol as this may increase the risk of adverse effects. To minimize the risk of particular adverse effects, doxylamine should not be used when taking any medication classified as a monoamine oxidase inhibitor (MAOI), and should be used with caution, if at all, when certain medical conditions are present. Because doxylamine is small enough on a molecular weight basis to pass into breastmilk, women should not breastfeed while using products with doxylamine as this may lead to adverse effects in the breastfed infant.
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