Meclizine hydrochloride is used in the prevention and treatment of nausea, vomiting, and/or vertigo associated with motion sickness. Meclizine is most effective against motion sickness when given prophylactically, although susceptibility to motion sickness may vary with the patient's age, previous exposure to motion, and the type, severity, and duration of motion. Although scopolamine generally is considered to be the most effective drug for the treatment of motion sickness, most clinicians prefer an antihistamine such as meclizine because it produces fewer adverse anticholinergic effects than does scopolamine. Meclizine and dimenhydrinate generally are considered to be equally effective in the treatment of motion sickness, but dimenhydrinate causes drowsiness more frequently. Meclizine has a longer duration of action than scopolamine and most other antihistamines. Promethazine may be more effective than other antihistamines in the treatment of motion sickness.
Meclizine has been used in the symptomatic treatment of vertigo associated with diseases affecting the vestibular system (e.g., labyrinthitis, Meniere's disease), but the value of the drug in these conditions has not been established. Like other antihistamines, meclizine is less effective than the phenothiazines in controlling nausea and vomiting not related to vestibular stimulation.
Although meclizine is a histamine H1-receptor antagonist, its use in allergic states has not been evaluated.
Dosage and Administration
Meclizine hydrochloride is administered orally.
For the prevention and treatment of nausea, vomiting, and/or vertigo associated with motion sickness, the usual oral dosage of meclizine hydrochloride in adults and children 12 years of age or older is 25-50 mg once daily or as directed by a physician. For the prevention of motion sickness, 25-50 mg of the drug may be given 1 hour before exposure to motion.
For the control of vertigo associated with diseases affecting the vestibular system, the usual adult dosage is 25-100 mg daily, administered in divided doses.
For further information on pharmacology, cautions, and acute toxicity in therapy with meclizine, see the Antihistamines General Statement 4:00.
Drowsiness, fatigue, dry mouth, and, rarely, blurred vision have occurred after administration of meclizine.
Precautions and Contraindications
Patients should be warned that meclizine may impair their ability to perform hazardous activities requiring mental alertness or physical coordination (e.g., operating machinery, driving a motor vehicle). In addition, additive CNS depression may occur when antihistamines, such as meclizine, are administered concomitantly with other CNS depressants including barbiturates, tranquilizers, and alcohol. If meclizine is used concomitantly with other depressant drugs, caution should be used to avoid overdosage. The anticholinergic effects of the drug should be considered when administering meclizine to patients with angle-closure glaucoma or prostatic hypertrophy.
Meclizine is contraindicated in patients who are hypersensitive to it.
Safety and efficacy of meclizine in children younger than 12 years of age have not been established; therefore, the manufacturers state that use of the drug in this age group is not recommended. If the drug is used in this age group (e.g., for the prevention and treatment of nausea, vomiting, and/or vertigo associated with motion sickness), it should be only under the advice and supervision of a physician.
Meclizine is teratogenic in animals. Although retrospective studies in humans suggest that the use of meclizine during pregnancy is probably not associated with teratogenic effects, the manufacturers state that the drug is contraindicated in women who are or may become pregnant.
The onset of action of meclizine hydrochloride is about 1 hour and the drug has a prolonged duration of action, with effects persisting 8-24 hours following administration of a single oral dose. The drug has a plasma half-life of 6 hours. The metabolic fate of meclizine in humans is unknown. In rats, meclizine is metabolized (probably in the liver) to norchlorcyclizine. This metabolite is distributed throughout most body tissues and crosses the placenta. The drug is excreted in feces unchanged and in urine as norchlorcyclizine.