Drug interactions
Fosamprenavir + Methadone
Severity: Moderate
Fosamprenavir and Methadone: 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
Fosamprenavir, given with ritonavir or alone, can alter methadone exposure. Methadone concentrations may change unpredictably, and some patients develop opioid withdrawal while others show excess opioid effect or QT prolongation.
What this interaction means in plain words
Fosamprenavir and Methadone 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
Amprenavir has mixed CYP3A4 inhibition and induction effects, and may also induce other methadone-metabolizing enzymes, so methadone exposure can fall or rise.
What to do
Monitor for withdrawal symptoms and for sedation or respiratory depression when starting or stopping fosamprenavir. Adjust the methadone dose according to clinical response, and consider an ECG if risk factors for QT prolongation exist.
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 Methadone
- Alvimopan + Methadone Contraindicated
- Calcium / magnesium / potassium / sodium oxybates + Methadone Contraindicated
- Droperidol + Methadone Contraindicated
- Ibutilide + Methadone Contraindicated
- Isocarboxazid + Methadone Contraindicated
- Lefamulin + Methadone Contraindicated
Frequently asked questions
Can I take Fosamprenavir with Methadone?
MediHelp rates the interaction as moderate. Fosamprenavir and Methadone 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. Fosamprenavir, given with ritonavir or alone, can alter methadone exposure. Methadone concentrations may change unpredictably, and some patients develop opioid withdrawal while others show excess opioid effect or QT prolongation.
How serious is the interaction between Fosamprenavir and Methadone?
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 withdrawal symptoms and for sedation or respiratory depression when starting or stopping fosamprenavir. Adjust the methadone dose according to clinical response, and consider an ECG if risk factors for QT prolongation exist.
What other medicines interact with Methadone?
MediHelp also lists interactions of Methadone with, for example, Alvimopan, Calcium / magnesium / potassium / sodium oxybates, Droperidol. The full list is on the Methadone page.
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