Pharmacokinetics and Safety of Tenofovir Alafenamide in HIV-Uninfected Subjects with Severe Renal Impairment

Tenofovir alafenamide (TAF) is an oral prodrug of tenofovir (TFV) that has greater stability in plasma than TFV disoproxil fumarate (TDF) and circulates as intact TAF, resulting in the direct and higher lymphatic loading of and exposure to TFV diphosphate, the active moiety. Unlike TFV, TAF is minimally eliminated in urine. The pharmacokinetics (PK) of TAF and TFV in HIV-uninfected subjects with severe renal impairment and matched healthy controls were evaluated. Subjects with severe renal impairment (RI; estimated glomerular filtration rate [eGFR], 15 to 29 ml/min) and controls (eGFR,>= 90 ml/min) matched for age, gender, and body mass index received a single dose of TAF at 25 mg. Blood and urine samples for TAF and TFV PK determinations were collected over 7 days postdosing, and subjects were followed up at 14 days. A total of 14 renally impaired subjects and 13 control subjects enrolled and completed the study. The TAF maximum observed concentration in plasma (C-max) and the area under the concentration-versus-time curve (AUC) extrapolated to infinite time (AUC(inf)) were 79% and 92% higher, respectively, in subjects with severe RI than the controls, primarily due to higher absorption. The TFV Cmax and AUCinf were 2.8-fold and 5.7-fold higher, respectively, in subjects with severe RI than the controls. In subjects with severe RI, TAF at 25 mg provided a TFV AUC 10 to 40% lower than that from historical TDF-based TFV exposures in subjects with normal renal function. There were no discontinuations due to adverse events. In subjects with severe RI receiving TAF at 25 mg, TAF exposures were higher than those for the controls; these differences are unlikely to be clinically meaningful. TFV exposures were higher than those for the controls but lower than the exposures in nonrenally impaired subjects on TDF-based regimens.