OBJECTIVES : Extensive but fragmented data from existing studies were used to
describe the drug-drug interaction between rifabutin and HIV-protease inhibitors, and
predict doses achieving recommended therapeutic exposure for rifabutin in patients with
HIV-associated tuberculosis, with concurrently administered protease inhibitors.
MATERIALS AND METHODS : Individual level data from 13 published studies were
pooled, and a population analysis approach was used to develop a pharmacokinetic model
for rifabutin, its main active metabolite 25-O-desacetyl rifabutin (des-rifabutin), and
drug-drug interaction with protease inhibitors in healthy volunteers and patients who had
HIV and tuberculosis (TB/HIV).
RESULTS : Key parameters of rifabutin affected by drug-drug interaction in TB/HIV
were clearance to routes other than des-rifabutin (reduced by 76%-100%), formation to
the metabolite (increased by 224% in patients), volume of distribution (increased by
606%), and distribution to the peripheral compartment (reduced by 47%). For desrifabutin,
the clearance was reduced by 35% to 76% and volume of distribution increased
by 67% to 240% in TB/HIV. These changes resulted in overall increased exposure to
rifabutin in TB/HIV patients by 210% because of the effects of protease inhibitors and
280% with ritonavir-boosted protease inhibitors.
CONCLUTION : Given together with nonboosted or ritonavir-boosted protease
inhibitors, rifabutin at 150 mg once daily results in similar or higher exposure compared
with rifabutin at 300 mg once daily without concomitant protease inhibitors, and may
achieve peak concentrations within acceptable therapeutic range. Although 300 mg rifabutin every three days with boosted protease inhibitor achieves an average equivalent
exposure, intermittent doses of rifamycins are not supported by current guidelines.