Rifabutin Trimethoprim/Sulfamethoxazole

Items 6-7 A patient with AIDS has a CD4 count of 45/ xL. He is being maintained on a three-drug regimen of indinavir, zalcitabine, and zidovudine. For prophylaxis against opportunistic infections, he is also receiving cidofovir, fluconazole, rifabutin, and trimethoprim-sulfamethoxazole. 

Items 92-93. A 30-year-old hospitalized AIDS patient has a CD4 cell count of 50/ tL. He is being treated with a highly active antiretroviral therapy (HAART) regimen consisting of zidovudine (ZDV), lamivudine (3TC), and indinavir. Other drugs being administered to this patient include acyclovir, clarithromycin, foscamet, rifabutin, and trimethoprim-sulfamethoxazole. 

Select an antibiotic regimen based on drug susceptibility of the cultured organism Start treatment with INH and pyrazinamide Treat the patient with clarithromycin, ethambutol, and rifabutin Treat with trimethoprim-sulfamethoxazole... 

Because of indinavir s metabolism, a number of drug interactions are possible. Indinavir interacts with rifabutin or ketoconazole, leading to increased or decreased indinavir concentration, respectively, in the blood plasma. Administration of drug combinations of indinavir with antiviral nucleoside analogues, cimetidine, quinidine, trimethoprim/sulfamethoxazole, fluconazole, or isoniazid resulted in an increased activity of indinavir. Indinavir is ... 

The pharmacokinetics of trimethoprim are not significantly affected by rifabutin, and probably not by rifampicin (rifampin). Rifabutin does not affect the pharmacokinetics of sulfamethoxazole, but significantly increases exposure to its hydroxylamine metabolite and as a result may increase adverse reactions to sulfamethoxazole in HIV-positive patients. 

Lee BL, Lampiris H, Colbom DC, Lewis RC, Narang PK, Sullam P The effect of rifabutin (RBT) on the pharmacokinetics (PK) of trimethoprim-sulfamethoxazole (TMP-SMX) in HIV-infected patients Intersci Ccmf Antimicrob Agents Chemoffier (1995) 35, 7... 

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