Dimenhydrinat

Dimenhydrinate is a medication used to prevent and treat motion sickness and related nausea and vomiting. It is a salt formed from diphenhydramine, an antihistamine, and chlorotheophylline, a theophylline derivative. The combination provides antiemetic effects with sedative properties.

Mechanism of action: It acts as a central nervous system–active antihistamine, blocking H1 receptors, and has anticholinergic effects that help reduce signals from the vestibular system to the brain’s vomiting center. The chlorotheophylline component adds mild stimulant activity, but the preparation remains sedating for many people.

Indications and availability: Used to prevent and treat motion sickness, seasickness, and associated nausea. It is commonly sold over the counter and used for short-term management of nausea, including postoperative nausea when appropriate. Dosing for adults typically ranges from 50 mg to 100 mg every 4 to 6 hours as needed, not to exceed about 400 mg per day; pediatric dosing depends on age and product labeling.

Pharmacokinetics: After oral administration, dimenhydrinate is absorbed and rapidly converted to its active diphenhydramine component. Onset of action is usually within 30 to 60 minutes, with peak effects within 1 to 2 hours. The drug is metabolized in the liver and excreted mainly in the urine. The half-life is several hours and can be prolonged in elderly individuals or those with liver impairment.

Adverse effects and cautions: The most common adverse effect is drowsiness; anticholinergic effects include dry mouth, blurred vision, and urinary retention. It can impair thinking or driving and should be used with caution in elderly people and in individuals with glaucoma, urinary retention, or peptic ulcers. Alcohol and other sedatives increase sedation risk. It is generally not recommended for infants or very young children; consult labeling.

Pregnancy and lactation: Data are limited; use only if clearly needed and after medical advice.