Cyclophosphamide and Ritonavir interaction
Cyclophosphamide and Ritonavir: both prescribing labels describe an interaction that usually calls for monitoring, a dose change, or spacing the doses.
Usually manageable with monitoring or a dose change. Tell your pharmacist you take both.
What the FDA labels say
From the Ritonavir (Norvir) label · effective 2026-07-23
Immunosuppressants: cyclosporine, tacrolimus, sirolimus (rapamycin) ↑ immunosuppressants Therapeutic concentration monitoring is recommended for immunosuppressant agents when co-administered with ritonavir.
From the Cyclophosphamide (Frindovyx) label · effective 2026-08-26
Effect of Other Drugs on Cyclophosphamide Exposure Protease Inhibitors Concomitant use of protease inhibitors may increase the concentration of cytotoxic metabolites and may enhance the toxicities of cyclophosphamide, including higher incidence of infections, neutropenia, and mucositis.
Monitor for increased toxicities in patients receiving protease inhibitors.
…toxicities: ● Azathioprine: Increased risk of hepatotoxicity (liver necrosis) ● Busulfan: Increased incidence of hepatic veno-occlusive disease and mucositis has been reported. ● Protease inhibitors: Increased incidence of mucositis Increased risk of hemorrhagic cystitis ● Radiation treatment: Increased risk of hemorrhagic cystitis may result from a combined…
Taking more than these two? Interactions stack. Check your whole list at once; it stays in your browser.
Open in the checkerNot medical advice. Interaction Checker quotes FDA label text and NIH fact sheets. Whether an interaction matters for you depends on doses, timing, kidney and liver function, and other conditions. Confirm with a pharmacist or prescriber.