Meclizine Hydrochloride

The recommended dosage is 25 mg to 100 mg daily administered orally, in divided doses, depending upon clinical response.

Tablets

Meclizine hydrochloride tablets must be swallowed whole.

Since drowsiness may occur with use of meclizine hydrochloride, patients should be warned of this possibility and cautioned against driving a car or operating dangerous machinery.

Patients should avoid alcoholic beverages while taking meclizine hydrochloride [see Drug Interactions (7.1)].

Because of its potential anticholinergic action, meclizine hydrochloride should be used with caution in patients with asthma, glaucoma, or enlargement of the prostate gland.

There may be increased CNS depression when meclizine hydrochloride is administered concurrently with other CNS depressants, including alcohol [see Warnings and Precautions (5.1)].

Based on in-vitro evaluation, meclizine is metabolized by CYP2D6. Therefore, there is a possibility for a drug interaction between meclizine hydrochloride and CYP2D6 inhibitors. Therefore, monitor for adverse reactions and clinical effect accordingly.

Risk Summary

Data from epidemiological studies have not generally indicated a drug-associated risk of major birth defects with meclizine during pregnancy. However, in a published study, an increased incidence of fetal malformations was observed following oral administration of meclizine to pregnant rats during the period of organogenesis, at doses similar to those used clinically. In the U.S. general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively. The background risk of major birth defects and miscarriage for the indicated population is unknown.

Data

Human Data

Epidemiological studies reporting on pregnancies exposed to meclizine have not identified an association between the use of meclizine during pregnancy and an increased risk of major birth defects.

Animal Data

In a published study, oral administration of meclizine (25 mg/kg to 250 mg/kg) to pregnant rats during the period of organogenesis resulted in a high incidence of fetal malformations. These effects occurred at doses as low as 25 mg/kg, which is approximately 2 times the maximum recommended human dose (100 mg) on a body surface area (mg/m²) basis.

Risk Summary

There are no data on the presence of meclizine in human milk, the effects on the breastfed infant, or the effects on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother's clinical need for meclizine hydrochloride and any potential adverse effects on the breastfed infant from meclizine hydrochloride or from the underlying maternal condition.

Safety and effectiveness in pediatric patients have not been established.

In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

The effect of hepatic impairment on the pharmacokinetics of meclizine has not been evaluated. As meclizine hydrochloride undergoes metabolism, hepatic impairment may result in increased systemic exposure of meclizine. Treatment with meclizine hydrochloride should be administered with caution in patients with hepatic impairment.

The effect of renal impairment on the pharmacokinetics of meclizine has not been evaluated. Because of a potential for drug/metabolite accumulation, meclizine hydrochloride should be administered with caution in patients with renal impairment and in the elderly, as renal function generally declines with age.

The genetic polymorphism of CYP2D6 that results in poor-, intermediate-, extensive-, and ultrarapid metabolizer phenotypes could contribute to large inter-individual variability in meclizine exposure. Therefore, when meclizine hydrochloride is administered to patients with CYP2D6 polymorphism, monitor for adverse reactions and clinical effect accordingly.

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

There are no relevant pharmacodynamic data regarding meclizine.

The available pharmacokinetic information for meclizine following oral administration has been summarized from published literature.

Absorption

Meclizine is absorbed after oral administration with maximum plasma concentrations reaching at a median T_max value of 3 hours post-dose (range: 1.5 to 6 hours) for the tablet dosage form.

Distribution

Drug distribution characteristics for meclizine in humans are unknown.

Elimination

Meclizine has a plasma elimination half-life of about 5 to 6 hours in humans.

Metabolism In an in vitro metabolic study using human hepatic microsome and recombinant CYP enzyme, CYP2D6 was found to be the dominant enzyme for metabolism of meclizine.

Carcinogenesis

Animal studies to assess the carcinogenic potential of meclizine have not been conducted.

Mutagenesis

Genetic toxicology studies of meclizine have not been conducted.

Impairment of Fertility

Animal studies to assess the effects of meclizine on fertility and early embryonic development have not been conducted.