Aripiprazole

Aripiprazole (brand name Abilify) is an atypical antipsychotic medication approved for the treatment of several psychiatric disorders. It is prescribed widely for its favorable side effect profile compared to older antipsychotics.

This drug is indicated for schizophrenia, bipolar I disorder (acute manic and mixed episodes), adjunctive treatment of major depressive disorder, and irritability associated with autistic disorder. Its versatility makes it a common choice in both inpatient and outpatient settings.

Aripiprazole works by modulating neurotransmitter systems in the brain. It acts as a partial agonist at dopamine D₂ receptors and serotonin 5-HT₁A receptors, while antagonizing serotonin 5-HT₂A receptors. This balanced activity helps stabilize mood and reduce psychotic symptoms.

The primary gene involved in aripiprazole metabolism is CYP2D6, a member of the cytochrome P450 enzyme family. CYP2D6 is responsible for oxidizing and clearing many psychiatric medications, including aripiprazole and its active metabolite, dehydroaripiprazole.

Genetic variations in CYP2D6 can alter the enzyme’s function, ranging from no activity (poor metabolizers) to very high activity (ultrarapid metabolizers). These changes can affect how quickly the drug is processed and eliminated, influencing both efficacy and risk of side effects. A “poor metabolizer” may clear the drug slowly and experience higher concentrations, while an “ultrarapid metabolizer” may clear it too fast for full therapeutic effect.

CYP2D6 metabolizer status can significantly influence aripiprazole plasma levels. Poor metabolizers tend to have higher blood concentrations and an increased risk of adverse reactions, whereas ultrarapid metabolizers may have subtherapeutic levels and reduced efficacy. Intermediate and normal metabolizers generally exhibit expected drug exposure and response.

Ultrarapid Metabolizer

• Effect on drug levels: Lower than expected plasma concentrations
• Clinical consequence: Potential reduced efficacy and risk of treatment failure
• Side effects: Generally fewer side effects but possible return of psychotic or mood symptoms

Normal Metabolizer

• Effect on drug levels: Within expected therapeutic range
• Clinical consequence: Standard efficacy and tolerability profile
• Side effects: Typical risk of akathisia, sedation, and weight gain

Intermediate Metabolizer

• Effect on drug levels: Moderately increased plasma concentrations
• Clinical consequence: Slightly elevated risk of adverse effects
• Side effects: Possible mild akathisia or sedation, monitor closely

Poor Metabolizer

• Effect on drug levels: Significantly higher than expected concentrations
• Clinical consequence: Increased risk of adverse reactions
• Side effects: Higher likelihood of akathisia, sedation, extrapyramidal symptoms; severity can be moderate to severe

Indeterminate/Not Available

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

CYP2D6 Dosing Guideline

The FDA guideline does not provide specific alternate drug recommendations for CYP2D6-related dosing. In clinical practice, alternative atypical antipsychotics such as risperidone, quetiapine, or olanzapine may be considered based on patient response and tolerance. These examples are for informational purposes only and not medical advice.

• FDA – Table of Pharmacogenetic Associations