Drug interactions
Cyclophosphamide + Ritonavir
Severity: Moderate
Cyclophosphamide and Ritonavir: 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
Ritonavir inhibits CYP3A4 and may affect CYP2B6, enzymes involved in converting cyclophosphamide to its active and toxic metabolites. The net effect on active metabolite exposure is uncertain, so efficacy or toxicity such as myelosuppression may change.
What this interaction means in plain words
Cyclophosphamide and Ritonavir 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.
Cyclophosphamide belongs to Oncology; Ritonavir belongs to Anti Virals.
Why it happens
Ritonavir inhibits CYP3A4 and may modulate CYP2B6, altering cyclophosphamide bioactivation and clearance.
What to do
Monitor blood counts and signs of cyclophosphamide toxicity or reduced response. Consider an alternative antiretroviral without strong CYP inhibition where feasible.
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 Cyclophosphamide
Other interactions of Ritonavir
- Alfuzosin + Ritonavir Contraindicated
- Amiodarone + Ritonavir Contraindicated
- Avanafil + Ritonavir Contraindicated
- Colchicine + Ritonavir Contraindicated
- Dronedarone + Ritonavir Contraindicated
- Eletriptan + Ritonavir Contraindicated
Frequently asked questions
Can I take Cyclophosphamide with Ritonavir?
MediHelp rates the interaction as moderate. Cyclophosphamide and Ritonavir 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. Ritonavir inhibits CYP3A4 and may affect CYP2B6, enzymes involved in converting cyclophosphamide to its active and toxic metabolites. The net effect on active metabolite exposure is uncertain, so efficacy or toxicity such as myelosuppression may change.
How serious is the interaction between Cyclophosphamide and Ritonavir?
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 blood counts and signs of cyclophosphamide toxicity or reduced response. Consider an alternative antiretroviral without strong CYP inhibition where feasible.
What other medicines interact with Cyclophosphamide?
MediHelp also lists interactions of Cyclophosphamide with, for example, Adenovirus types 4 and 7 live, Belatacept, Bendamustine. The full list is on the Cyclophosphamide page.
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