The precise mechanism by which meclizine exerts its therapeutic effect is unknown but is presumed to involve antagonism of the histamine H1 receptor.

Based on a review of this drug by the National Academy of Sciences - National Research Council and/or other information, the FDA has classified the indications as follows: Effective: Management of nausea and vomiting, and dizziness associated with motion sickness. Possibly Effective: Management of vertigo associated with diseases affecting the vestibular system. Final classification of the less-than-effective indications requires further investigation.

Vertigo: For the control of vertigo associated with diseases affecting the vestibular system, the recommended dose is 25 to 100 mg daily, in divided dosage, depending upon clinical response. Motion Sickness: The initial dose of 25 to 50 mg of Antivert should be taken one hour prior to embarkation for protection against motion sickness. Thereafter, the dose may be repeated every 24 hours for the duration of the journey.

Anaphylactoid reaction, drowsiness, dry mouth, headache, fatigue, vomiting and, on rare occasions, blurred vision have been reported.

Meclizine HCl is contraindicated in individuals who have shown a previous hypersensitivity to it.

Nursing Mothers: It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when meclizine is administered to a nursing woman. Hepatic Impairment: The effect of hepatic impairment on the pharmacokinetics of meclizine has not been evaluated. As meclizine undergoes metabolism, hepatic impairment may result in increased systemic exposure of the drug. Treatment with meclizine should be administered with caution in patients with hepatic impairment. See package insert for complete information.