The bioavailability of
rifabutin is increased by
amprenavir,
atazanavir, indinavir, nelfinavir, and especially
ritonavir, with an increased risk of
toxicity.
Rifabutin decreases the bioavailability of indinavir, nelfinavir, and particularly saquinavir (with an increased risk of therapeutic failure) but has no effect on
amprenavir,
atazanavir and ritonavir-boosted fosamprenavir.
The combination of
rifabutin with
protease inhibitors may be used, but large dosage reductions of
rifabutin and/or increases in the doses of the
protease inhibitors are often necessary. The treatment of
tuberculosis in patients taking antiretrovirals is complex and up-to-date guidelines should be consulted.