Pharmacokinetic interactions between cobicistat-boosted elvitegravir and darunavir in HIV-infected patients.

Objectives: To evaluate if there are significant drug-drug interactions between cobicistat-boosted elvitegravir and 800mg darunavir once daily taken simultaneously, as has been suggested previously. Methods: The study population consisted of three groups of unselected volunteers taking a regimen of elvitegravir, cobicistat, emtricitabine and tenofovir disoproxil fumarate (150, 150, 200 and 300mg, respectively) co-formulated in a single tablet plus 800mg darunavir (group A); only co-formulated elvitegravir, cobicistat, emtricitabine and tenofovir disoproxil fumarate (group B); and cobicistat-boosted darunavir (800mg darunavir +150mg cobicistat) plus two nucleos(t) ide analogues (group C). Elvitegravir, cobicistat and darunavir concentrations at the end of the dosing interval (C-24) were quantified using a validated LCwith tandemMSmethod. Results: A total of 170 samples were obtained from 24, 32 and 32 patients in groups A, B and C, respectively. In group A, the elvitegravir C-24 were similar to those in group B (233.67 versus 250.39 ng/ mL) (P = 0.406) and the darunavir C-24 were similar to those in group C (1293.54 versus 1319.34 ng/ mL) (P = 0.908). The cobicistat C-24 were comparable in groups A and B (20.2 versus 20.9 ng/ mL) and slightly higher in group C (27.7 ng/ mL) (P = 0.059). Conclusions: The results provide evidence of similar elvitegravir and darunavir C24 concentrations when these drugs are co-administered as co-formulated elvitegravir, cobicistat, emtricitabine and tenofovir disoproxil fumarate plus 800mg darunavir or dosed separately.