Cidofovir with probenecid modestly decreased levels of trimethoprim and sulfamethoxazole (co-trimoxazole),and caused moderate increases in didanosine levels, but did not alter fluconazole pharmacokinetics. None of these drugs altered cidofovir pharmacokinetics.
In a study,6 HIV-positive subjects were given co-trimoxazole 960mg daily with a single 3-mg/kg dose of cidofovir with probenecid given on day 7. The AUC and maximum plasma concentrations of both trimethoprim and sulfamethoxazole were decreased by about 30 % and renal clearance was significantly increased. The pharmacokinetics of cidofovir were not affected (See reference number 1).
In a study,6 HIV-positive subjects were given didanosine 100 or 200mg twice daily for 7 days with a single 3-mg/kg dose of cidofovir with probenecid given on day 7. The AUC of didanosine was increased 1.6-fold, but pharmacokinetics of cidofovir were not affected (See reference number 1).
In a study,6 HIV-positive subjects were given fluconazole 100mg daily for 13 days with a single 3-mg/kg dose of cidofovir with probenecid given on day 13. The pharmacokinetics of both drugs were unaffected (See reference number 1).
It was suggested that cidofovir/probenecid might alter renal elimination of these drugs (See reference number 1)
The modest decreases in trimethoprim and sulfamethoxazole levels, and moderate increases in didanosine levels caused by cidofovir are considered unlikely to be clinically relevant because of infrequent dosing schedule of cidofovir/probenecid. No dose adjustments are considered necessary (See reference number 1).
1. Luber A,Lalezari J, Rooney J, Jaffe H, Flaherty J. Drug-drug interaction study with intravenous cidofovir (CDV) and either trimethoprim/sulfamethoxazole (TMP/SMX), didanosine(DDI), or fluconazole (FLU) in HIV-infected individuals. Intersci Conf Antimicrob Agents Chemother (2002) 42, 27.