Doxylamine

Doxylamine is a first-generation antihistamine used as a short-term sedative and hypnotic (sleep aid) or in combination formulations to provide night-time allergy and cold relief. It provides a calmative effect in preparations containing the analgesics paracetamol (acetaminophen) and codeine. It is prescribed in combination with vitamin B6 (pyridoxine) to prevent morning sickness in pregnant women. Its fetal safety rating is 'A' (no evidence of risk) in Briggs' Reference Guide to Fetal and Neonatal Risk. It was first described in 1948. Doxylamine is an antihistamine used to treat sneezing, runny nose, watery eyes, hives, skin rash, itching, and other cold or allergy symptoms. It is also used as a short-term treatment for sleep problems (insomnia). It is used in the combination drug pyridoxine/doxylamine to treat nausea and vomiting of pregnancy. As of 2004, doxylamine and diphenhydramine were the agents most commonly used to treat short-term insomnia. As of 2008, antihistamines were not recommended by the American Academy of Sleep Medicine for treatment of chronic insomnia 'due to the relative lack of efficacy and safety data'. Doxylamine succinate is a potent anticholinergic and has a side-effect profile common to such drugs, including dry mouth, ataxia, urinary retention, drowsiness, memory problems, inability to concentrate, hallucinations, psychosis, and a marked increased sensitivity to external stimuli. Like many hypnotics, it should not be combined with other antihistamines, such as cetirizine (Zyrtec) or diphenhydramine (Benadryl), as this combination can increase the risk of serious side effects. Some people can have a different reaction: instead of sedating, it stimulates. Using doxylamine over a long period of time is not recommended. However, the drug is not addictive. It can be mildly psychologically addictive to some people. If used for longer periods of time, withdrawal effects are unlikely to be experienced with prolonged use, but mild withdrawal symptoms are likely if taken long-term. Because of its relatively long elimination half-life (10–12 hours), doxylamine is associated with daytime/next-day drowsiness, grogginess, dry mouth, and tiredness when used as a hypnotic. The shorter elimination half-life of diphenhydramine (4–8 hours) may give it an advantage over doxylamine in this regard. Unlike with diphenhydramine, case reports of coma and rhabdomyolysis have been reported with doxylamine.