Increased tenofovir monoester concentrations in patients receiving tenofovir disoproxil fumarate with ledipasvir/sofosbuvir.

Background: Intracellular tenofovir diphosphate concentrations are markedly increased in HIV/HCV coinfected individuals receiving tenofovir disoproxil fumarate (TDF) with sofosbuvir-containing treatment. Sofosbuvir may inhibit the hydrolysis of TDF to tenofovir, resulting in increased concentrations of the disoproxil or monoester forms, which may augment cell loading. We sought to quantify tenofovir disoproxil and monoester concentrations in individuals receiving TDF with and without ledipasvir/sofosbuvir. Methods: HIV/HCV coinfected participants receiving TDF-based therapy were sampled pre-dose and 1 and 4 h post-dose prior to and 4 weeks after initiating ledipasvir/sofosbuvir. Tenofovir disoproxil was not detectable. Tenofovir monoester in plasma and tenofovir diphosphate in PBMC and dried blood spots (DBS) were quantified using LC-MS/MS. Geometric mean ratios (week 4 versus baseline) and 95% CIs were generated for the pharma-cokinetic parameters. P values reflect paired t-tests. Results: Ten participants had complete data. At baseline, geometric mean (95% CI) tenofovir monoester plasma concentrations at 1 and 4 h post-dose were 97.4 ng/mL (33.0-287.5) and 0.74 ng/mL (0.27-2.06), respectively. With ledipasvir/sofosbuvir, tenofovir monoester concentrations at 4 h post- dose were 5.02-fold higher (95% CI 1.40-18.05; P=0.019), but did not significantly differ at 1 h post-dose (1.72-fold higher, 95% CI 0.25-11.78; P=0.54), possibly due to absorption variability. Tenofovir diphosphate in PBMC and DBS were increased 2.80-fold (95% CI 1.71-4.57; P=0.001) and 7.31-fold (95% CI 4.47-11.95; P<0.0001), respectively, after 4 weeks of ledipasvir/sofosbuvir. Conclusions: Tenofovir monoester concentrations were increased in individuals receiving TDF with ledipasvir/sofosbuvir, consistent with inhibition of TDF hydrolysis. Additional studies are needed to determine the clinical relevance of this interaction.