CYP2D6 is a liver enzyme that metabolizes about 25% of all drugs, including antidepressants, antipsychotics, and pain medications. Genetic variations in this gene affect how quickly or slowly your body breaks down these medications.
Poor Metabolizer
Drug
Codeine
Effect
Poor metabolism → reduced efficacy
Recommendation
AVOID. Choose alternative analgesic.
CPIC Guideline
CPIC Level B
FDA Label
Black box warning: avoid in ultra-rapid metabolizers; caution in poor metabolizers
Ultra-Rapid Metabolizer
Drug
Codeine
Effect
Rapid metabolism → toxicity risk
Recommendation
AVOID. Increased morphine formation.
CPIC Guideline
CPIC Level A
FDA Label
Contraindicated in ultra-rapid metabolizers
Poor Metabolizer
Drug
Fluoxetine
Effect
Elevated plasma concentrations
Recommendation
ADJUST. Consider lower dose.
CPIC Guideline
CPIC Level C
FDA Label
Metabolism may be impaired
Poor Metabolizer
Drug
Paroxetine
Effect
Elevated plasma concentrations
Recommendation
ADJUST. Use standard dose; monitor for adverse effects.
CPIC Guideline
CPIC Level C
FDA Label
Consider dose adjustment
Poor Metabolizer
Drug
Venlafaxine
Effect
Reduced plasma levels → potential treatment failure
Recommendation
ADJUST. Consider higher dose or alternative.
CPIC Guideline
CPIC Level C
FDA Label
Consider dose adjustment in poor metabolizers
Clinical Action: These recommendations are based on CPIC guidelines and FDA labeling. Discuss results with your healthcare provider or genetic counselor to determine appropriate treatment adjustments.
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