Drug Interaction Report

MONITOR: Coadministration with fostemsavir may increase the plasma concentrations of drugs that are substrates of the transporters, organic anion transporting polypeptides (OATP) 1B1/1B3 and breast cancer resistance protein (BCRP). Temsavir, the active moiety of fostemsavir, is an inhibitor of OATP 1B1 and 1B3. Additionally, temsavir and two metabolites are inhibitors of BCRP. When a single 10 mg dose of rosuvastatin, an OATP 1B1/1B3 and BCRP substrate, was administered with fostemsavir 600 mg twice daily in 18 study subjects, mean rosuvastatin peak plasma concentration (Cmax) and systemic exposure (AUC) increased by 78% and 69%, respectively, compared to rosuvastatin administered alone.

MANAGEMENT: Caution is advised when fostemsavir is used concurrently with medications that are substrates of OATP 1B1/1B3 and/or BCRP, particularly those with a narrow therapeutic range. Dosage adjustments as well as clinical and laboratory monitoring may be appropriate for some drugs whenever fostemsavir is added to or withdrawn from therapy.

ADJUST DOSING INTERVAL: Oral cladribine may increase the bioavailability of other drugs, which may increase the risk or severity of adverse reactions. Cladribine tablets may contain hydroxypropyl betadex, which could form a complex with the active ingredients of other drugs, especially agents with low solubility. The clinical relevance of this interaction remains unknown.

MANAGEMENT: Administration of oral cladribine should be separated from any other oral drug by at least 3 hours.