Vyvanse and Cytochrome P450 Pathways
Vyvanse (lisdexamfetamine) does NOT act as a substrate, inhibitor, or inducer of CYP2D6, CYP2B6, or CYP1A2. However, CYP2D6 inhibitors can increase exposure to dextroamphetamine (Vyvanse's active metabolite), which has important clinical implications.
Metabolism of Vyvanse
Lisdexamfetamine is a prodrug that is not metabolized by cytochrome P450 enzymes. Instead, it is converted to dextroamphetamine by red blood cell hydrolysis 1. This unique metabolism distinguishes it from other ADHD medications like atomoxetine, which is primarily metabolized through CYP2D6 2.
Effect on CYP Enzymes
Vyvanse does not inhibit or induce CYP enzymes, including:
- CYP1A2: No dose adjustment needed for CYP1A2 substrates (e.g., theophylline, duloxetine, melatonin) when co-administered with Vyvanse 3
- CYP2D6: No dose adjustment needed for CYP2D6 substrates (e.g., atomoxetine, desipramine, venlafaxine) when co-administered with Vyvanse 3
- CYP2B6: Not mentioned in FDA labeling, but in vitro studies showed no inhibition 4
Research confirms this: In vitro testing demonstrated that lisdexamfetamine showed no concentration-dependent or mechanism-based inhibition of CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6, or CYP3A4 4. A clinical drug interaction study using the Cooperstown cocktail confirmed that Vyvanse did not alter the activity of CYP1A2, CYP2D6, CYP2C19, or CYP3A 5.
Clinical Implications: CYP2D6 Inhibitors and Vyvanse
While Vyvanse itself doesn't interact with these pathways, CYP2D6 inhibitors can affect Vyvanse's active metabolite (dextroamphetamine):
- Co-administration with CYP2D6 inhibitors may increase dextroamphetamine exposure and raise the risk of serotonin syndrome 3
- Initiate with lower Vyvanse doses when combining with CYP2D6 inhibitors
- Monitor for serotonin syndrome during initiation and dose increases
- If serotonin syndrome occurs, discontinue both Vyvanse and the CYP2D6 inhibitor 3
Recent research suggests CYP2D6 poor metabolizers may actually have higher odds of symptom improvement with amphetamines 6, though this requires further validation.
Key Takeaway
Vyvanse is pharmacokinetically "clean" regarding CYP450 interactions—it neither uses these pathways for its own metabolism nor interferes with other drugs metabolized by CYP1A2, CYP2B6, or CYP2D6. The only clinically relevant interaction is when CYP2D6 inhibitors are added, which can increase dextroamphetamine levels and require dose reduction of Vyvanse.