Drug interactions
Fosamprenavir + Tolterodine
Severity: Moderate
Fosamprenavir and Tolterodine: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Amprenavir, the active form of fosamprenavir, inhibits CYP3A4 and can raise tolterodine levels, mainly relevant when CYP2D6 is deficient or inhibited. Higher exposure increases anticholinergic adverse effects.
What this interaction means in plain words
Fosamprenavir and Tolterodine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
CYP3A4 inhibition by amprenavir (ritonavir-boosted regimens enhance this) reduces tolterodine clearance.
What to do
Monitor for anticholinergic effects and limit tolterodine to 1 mg twice daily if used with strong CYP3A4 inhibitors such as ritonavir-boosted regimens.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Tolterodine
Frequently asked questions
Can I take Fosamprenavir with Tolterodine?
MediHelp rates the interaction as moderate. Fosamprenavir and Tolterodine can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Amprenavir, the active form of fosamprenavir, inhibits CYP3A4 and can raise tolterodine levels, mainly relevant when CYP2D6 is deficient or inhibited. Higher exposure increases anticholinergic adverse effects.
How serious is the interaction between Fosamprenavir and Tolterodine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for anticholinergic effects and limit tolterodine to 1 mg twice daily if used with strong CYP3A4 inhibitors such as ritonavir-boosted regimens.
What other medicines interact with Tolterodine?
MediHelp also lists interactions of Tolterodine with, for example, Clarithromycin, Clozapine, Cobicistat. The full list is on the Tolterodine page.
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