Tenofovir Alafenamide for the Treatment of Chronic Hepatitis B Monoinfection

Tenofovir alafenamide (TAF) is indicated for adult patients with chronic hepatitis B virus (HBV) infection with compensated liver disease at an oral dose of 25mg/day. TAF is a more stable prodrug in the plasma than tenofovir disoproxil fumarate (TDF), leading to decreased plasma exposure of tenofovir. Decreased exposure is thought to reduce the risk of long-term TDF toxicities, such as nephrotoxicity and decreased bone mineral density (BMD). TAF, a nucleotide reverse transcriptase inhibitor, has the same mechanism of action as TDF. The results of phase III primary trials and extensions showed that TAF is noninferior to TDF at suppressing the HBV viral load in treatment-naive and treatment-experienced HBeAg-negative and HBeAg-positive patients at 48weeks, 96weeks, and 144weeks of therapy. The most commonly reported adverse events were headache, abdominal pain, fatigue, cough, nausea, and back pain. At all evaluated time points (out to 144wks of treatment), patients who received TAF had less risk of nephrotoxicity and less of a decline in BMD than the patients who received TDF. TAF appears to be safe in patients with a creatinine clearance (Cl-cr) above 15ml/min; however, TAF is not currently recommended in patients with an estimated Cl-cr below this threshold. TAF is safe in patients with mild hepatic impairment but is not currently recommended in patients with moderate or severe hepatic impairment (Child-Pugh class B or C).