|Trade names||Diclectin, Diclegis, Bendectin, others|
|Main uses||Nausea and vomiting of pregnancy|
|Side effects||Tiredness, lightheadedness, sleepiness, dry mouth|
|Breastfeeding||Pyridoxine (compatible), doxylamine (not recommended)|
Pyridoxine/doxylamine, sold under the brand name Diclectin among others, is a combination of pyridoxine (vitamin B6) and doxylamine. It is used for nausea and vomiting of pregnancy (morning sickness); though the benefit is small. It is taken by mouth.
Commons side effects include tiredness, lightheadedness, sleepiness, and a dry mouth. While concerns of birth defects were raised in 1983, these concerns turned out to be unfounded. Use in pregnancy is considered acceptable. How the combination works is unclear. Doxylamine is a first-generation antihistamine.
The combination came into medical use in 1976. A prior formulation that also contained dicyclomine; however, was in use in the United Kingdom since 1958. Based on taking 4 pills per day, the cost in the United Kingdom is £160 per month. The Scottish Medicines Consortium did not consider it cost effective as of 2019. In the United States this amount costs about 190 USD as of 2021.
The combination of pyridoxine, more commonly referred to as vitamin B6 and doxylamine is effective for the management of nausea and vomiting of pregnancy. A 2018 review, however, 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 is currently being phased out by the FDA.
The American Congress of Obstetricians and Gynecologists (ACOG) states that the recommendation of “taking Vitamin B6 or Vitamin B6 plus doxylamine is safe and effective and should be considered a first-line treatment” is based on consistent scientific evidence. This recommendation has been evaluated by the US Department of Health and Human Services’ Agency for Healthcare Research and Quality, who concur that the benefit of implementing the guideline recommendations would be a reduction on nausea and vomiting of pregnancy. The Society of Obstetricians and Gynaecologists of Canada (SOGC) published a Clinical Practice Guideline on the management of nausea and vomiting of pregnancy in which it states that the “doxylamine/pyridoxine combination should be the standard of care, since it has the greatest evidence to support its efficacy and safety”.
The Motherisk Program, at the Hospital for Sick Children in Toronto, recommends the combination of doxylamine and of pyridoxine as first-line therapy for the management of nausea and vomiting of pregnancy.
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.
Due to the extensive scientific evidence demonstrating that there is no difference in the risk for birth defects or other adverse pregnancy outcomes between infants whose mothers take pyridoxine/doxylamine during pregnancy and those infants whose mothers do not take this drug combination, the two ingredients of the drug are considered pregnancy compatible (or category A drugs with the previous pregnancy risk factor classification system).
Since the mid-1950s, over 33 million women have used the combination drug of pyridoxine/doxylamine in pregnancy, and scientific analysis on more than 200,000 exposed pregnancies has been conducted to determine if the combination of pyridoxine and doxylamine is harmful to the unborn baby. No epidemiological studies have found any teratogenic effect.
Two separate meta-analyses have been conducted that have assessed pregnancy outcomes following the use of a combination of pyridoxine and doxylamine with or without dicyclomine during the first trimester of pregnancy. The initial meta-analysis, published in 1988, combined data from 12 cohort and 5 case-control studies, and the subsequent meta-analysis, published in 1994, combined data from 16 cohort studies and 11 case control studies. These studies included over 200,000 Bendectin-exposed pregnancies and did not observe an increased risk for major malformations. Separate analyses were conducted for specific defects including cardiac defects, limb reduction defects, oral clefts, and genital tract malformations; no increased risks for these defects were found.
In 1989, a report on the safety of the drug combination of pyridoxine/doxylamine for use in the management of NVP was prepared by a panel of Canadian and American experts for the Special Advisory Committee on Reproductive Physiology to the Health Protection Branch of Health Canada (currently called the Health Products and Food Branch). These scientific experts concluded that “numerous studies in animals and in humans that have been reported in the scientific and medical literature demonstrate that Bendectin is not a teratogen. The safety of Bendectin/Diclectin in the management of nausea and vomiting of pregnancy has been established by its use in many thousands of pregnant women”.
A study was conducted to determine whether the combination drug of pyridoxine and doxylamine had an effect on the neurodevelopment of children exposed in utero. Results from this study observed no difference in intelligence quotient scores between children who were exposed to pyridoxine/doxylamine in utero and children who were not exposed.
The combination of doxylamine and vitamin B6 was first introduced to the US market as Bendectin in 1956. At that time, Bendectin was a 3 ingredients prescription medication. The third one, dicyclomine, a Pregnancy Category B anticholinergic/antispasmodic, was omitted from the formulation starting in 1976 due to its lack of efficacy.: 317  Bendectin (doxylamine/vitamin B6) was voluntarily removed from the market in 1983 by its manufacturer, Merrell Dow Pharmaceuticals, following numerous lawsuits alleging that it caused birth defects, although an FDA panel concluded that no association between Bendectin and birth defects had been demonstrated. In litigation, Bendectin was supposed to cause all kinds of fetal malformations and problems including limb and other musculoskeletal deformities, facial and brain damage, defects of the respiratory, gastrointestinal, cardiovascular and genital-urinary systems, blood disorders and cancer. The most famous case involving the drug is Daubert v. Merrell Dow Pharmaceuticals (1993). These suits were led by celebrity plaintiff attorney Melvin Belli . The star witness for the case against Bendectin, William McBride, was later found to have falsified research on teratogenic effects of the drug, and was struck off the medical register in Australia.
An extensive review of the evidence submitted in legal proceedings regarding Bendectin has been summarized and found no evidence that the drug in clinical use was linked to birth defects.
The FDA, in 1999, published a statement in the Federal Register that summarized their opinion regarding the safety of pyridoxine/doxylamine during pregnancy: “The FDA has determined that the drug product Bendectin, a tablet composed of pyridoxine hydrochloride 10 mg, and doxylamine succinate 10 mg, for the prevention of nausea of pregnancy was not withdrawn from the market for reasons of safety or effectiveness”.
On Monday April 8, 2013, the FDA approved the return of the doxylamine-pyridoxine combination under the new trademark name of Diclegis. The medication is manufactured by Duchesnay Inc.
In July 2015, the drug company came under considerable scrutiny for promoting its drug through the American celebrity Kim Kardashian through the social media platforms Facebook and Instagram.
In October 2015, Toronto, Canada physicians Drs. Navindra Persaud, Jessica Chin, and Mark Walker wrote a public letter to the Journal of Obstetrics and Gynaecology of Canada and raised concerns over the risks of Diclectin and recommended reconsidering it as the "first-line pharmacological treatment" against the nausea and vomiting of pregnancy. Dr. Persaud shared with news agencies that his only source of research data for this drug came from Health Canada and claimed he was only able to access the document by signing a confidentiality agreement.
Society and culture
The Bendectin case, and the subsequent removal of the drug from the US market, has had a number of consequences. Firstly, there was an immediate increase in the rates of hospitalization for nausea and vomiting in pregnancy. Secondly, it created a treatment void in terms of having a safe medication that could be used for alleviating morning sickness in US pregnant women, a condition which, in the most severe form, called hyperemesis gravidarum, could be both life-threatening and cause women to terminate their pregnancy. The lack of availability of a safe and effective drug for the treatment of nausea and vomiting of pregnancy resulted in the use of other, less studied drugs in pregnancy. Thirdly, it has been claimed that subsequent to the Bendectin experience, drug companies stayed away from developing medications for pregnant patients. As a result, only a few medications were approved by the FDA for obstetrical indications in the past several decades. Lastly, the perception that all medications are teratogenic increased among pregnant women and healthcare professionals. The unfounded fear of using medications during pregnancy has precluded many women from receiving the treatment they require.
From a legal perspective, the case through Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993) set a new standard for admitting expert testimony in federal courts in lieu of the Frye standard.
This medication in the U.S. is $528 (USD) for 100 tablets oral delayed release 10 mg
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