}

Meclizine

Antihistamines

Drug Overview

Meclizine is a first‐generation antihistamine marketed under brand names such as Antivert. It is commonly prescribed to prevent and treat nausea, vomiting, and dizziness associated with motion sickness or inner ear disorders.

This medication is indicated for the management of motion sickness and vertigo. By blocking H1 histamine receptors in the central nervous system, meclizine reduces vestibular stimulation and diminishes symptoms of nausea and imbalance.

Relevant Genes and Their Roles

CYP2D6 is the primary enzyme responsible for the hepatic metabolism of many drugs, including meclizine. It is part of the cytochrome P450 family, which transforms medications into more water‐soluble compounds for elimination.

Genetic variants in CYP2D6 can alter enzyme activity, leading to faster or slower drug clearance. Individuals with high activity may clear meclizine rapidly, reducing its effectiveness, while those with low activity may accumulate higher levels, increasing the risk of side effects.

Impact of Genetics on Drug Response

Depending on CYP2D6 phenotype—such as ultrarapid, normal, intermediate, or poor metabolizer—meclizine blood levels can vary widely. Ultrarapid metabolizers may experience subtherapeutic concentrations and reduced efficacy, whereas poor metabolizers can have elevated levels, heightening sedation and anticholinergic effects.

Expected Clinical Effects of Genetic Variation

Ultrarapid Metabolizer

  • Effect on drug levels: Lower plasma concentrations
  • Clinical consequence: Reduced efficacy
  • Side effects: Typically rare; low risk of sedation

Normal Metabolizer

  • Effect on drug levels: Expected plasma levels
  • Clinical consequence: Typical therapeutic response
  • Side effects: Standard sedation and dry mouth

Intermediate Metabolizer

  • Effect on drug levels: Moderately increased concentrations
  • Clinical consequence: May heighten sedation
  • Side effects: Mild to moderate sedation; occasional dry mouth

Poor Metabolizer

  • Effect on drug levels: Significantly increased concentrations
  • Clinical consequence: Higher risk of drowsiness and anticholinergic effects
  • Side effects: Severe sedation, dry mouth, constipation; rare but possible

Indeterminate/Not Available

  • Effect on drug levels: Unknown
  • Clinical consequence: No specific guidance; follow standard dosing with clinical monitoring
  • Side effects: Unknown

Dosing Guidelines

CYP2D6 Dosing Guideline

Phenotype Clinical Consequence Guideline Recommendation
Ultrarapid Metabolizer Potential for reduced drug exposure, possibly decreasing efficacy Monitor patient response; consider increasing dose if therapy is ineffective
Normal Metabolizer Expected drug exposure and typical therapeutic response Use standard dosing
Intermediate Metabolizer Moderately increased drug exposure, may heighten adverse effects Monitor for side effects; consider dose reduction if intolerable sedation occurs
Poor Metabolizer Significantly increased drug exposure, elevated risk of adverse reactions Monitor for adverse effects; consider dose reduction or alternative therapy
Indeterminate/Not available Unknown impact Initiate therapy with recommended starting dose

Alternative Treatment Options

The FDA guideline does not specify alternative drugs for meclizine. In clinical practice, alternatives such as dimenhydrinate or promethazine may be used for motion sickness; these examples are for illustration and not medical advice.

Sources and References

Disclaimer: This document is for informational purposes only and is not a substitute for medical advice. Clinical decisions should be made by a qualified healthcare professional.

Interested in learning more about how your genetics may affect your response to medication? Get started with Gene2Rx today.

I'm Interested