Duloxetine Metabolism and Drug Interactions

Patient Factors Affecting Metabolism

• Elderly female poor metabolizers of CYP2D6 are at increased risk for adverse effects due to elevated blood levels of duloxetine, with a 95% higher concentration-to-dose ratio compared to normal metabolizers, and may have threefold higher concentration-to-dose ratios compared to younger male normal metabolizers 1

Clinical Implications of CYP2D6 Status

• Patients with CYP2D6 poor metabolizer phenotype show significantly higher duloxetine levels at standard doses, which correlates with differences in treatment efficacy and side effect profiles, and for known CYP2D6 poor metabolizers, starting with lower doses is recommended 1

Drug Interactions

• The American College of Clinical Pharmacology recommends exercising caution when prescribing duloxetine with other medications metabolized by CYP2D6, particularly those with a narrow therapeutic index, and monitoring for increased effects of CYP2D6 substrates when co-administered with duloxetine 1

Discontinuation Considerations

• The guideline society recommends gradual tapering when discontinuing duloxetine to minimize withdrawal symptoms, due to its metabolism profile 2