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Purpose This study evaluated the single- and multiple-dose pharmacokinetic (PK) variables of elbasvir and grazoprevir in healthy Chinese individuals. Methods This study was a 2-part, parallel-arm, open-label trial. In part 1, single-dose PK variables of elbasvir 10/50/100 mg and grazoprevir 50/100/200 mg were evaluated in 10 participants per drug. In part 2, 10-day multiple-dose PK variables of elbasvir 50 mg and grazoprevir 100 mg administered once daily alone and in combination were evaluated in 12 participants. Summary and inferential statistics of the PK parameters are reported. Elbasvir and grazoprevir PK parameters were also compared between Chinese participants and historical data from white participants. Findings Single-dose elbasvir and grazoprevir median Tmax were 2.9 to 4.0 and 1.9 to 3.0 hours after administration, respectively. Elbasvir AUC0–∞ and Cmax increased in a dose-proportional manner (slope estimate [90% CI], 0.92 [0.84–1.01] and 0.98 [0.86–1.09], respectively), whereas grazoprevir AUC0–∞ and Cmax increased in a greater-than-dose-proportional manner (slope estimate [90% CI], 1.42 [1.27–1.57] and 1.96 [1.64–2.29]). After repeated administration, the accumulation ratios for AUC0–24, 24-hour concentration, and Cmax were 1.55, 1.57, and 1.38 for elbasvir and 2.03, 1.23, and 2.51 for grazoprevir. Co-administration of elbasvir 50 mg and grazoprevir 100 mg once daily did not have a clinically relevant effect on the PK variables of either drug. Median Tmax after co-administration versus alone was 3.0 hours versus 3.0 hours for elbasvir and 3.1 hours versus 3.0 hours for grazoprevir. Geometric mean ratios (90% CI) for elbasvir and grazoprevir AUC0–24 (Chinese/white participants) were 1.58 (1.03–2.42) and 1.21 (0.76–1.92). Elbasvir and grazoprevir, administered alone or concomitantly, were well tolerated. Implications In healthy Chinese individuals, administration of elbasvir and grazoprevir, alone or concomitantly, was generally well tolerated, with a thoroughly characterized PK profile. Elbasvir and grazoprevir exposures may trend higher in Chinese healthy participants relative to white healthy participants. Protocol number MK-5172 PN022.

Purpose Elbasvir (MK-8742) and grazoprevir (MK-5172; Merck & Co, Inc, Kenilworth, New Jersey) are hepatitis C virus (HCV)-specific inhibitors of the nonstructural protein 5A phosphoprotein and the nonstructural protein 3/4A protease, respectively. The aims of these studies were to evaluate the antiviral activity and safety of different doses of elbasvir or grazoprevir each administered as monotherapy to participants infected with either HCV genotype (GT) 1 or GT3. Methods These 2 double-blind, randomized, placebo-controlled, sequential-panel, multiple ascending dose studies were conducted to assess the safety and pharmacodynamics of 5 days of once-daily elbasvir or 7 days of once-daily grazoprevir in adult male participants chronically infected with either HCV GT1 or GT3. Findings Oral administration of elbasvir or grazoprevir once daily exhibited potent antiviral activity in participants with chronic GT1 or GT3 HCV infections. HCV RNA levels declined rapidly (within 1 day for elbasvir and 2 days for grazoprevir). At 50 mg of elbasvir once daily, the mean maximum reductions in HCV RNA from baseline were 5.21, 4.17, and 3.12 log10 IU/mL for GT1b-, GT1a-, and GT3-infected participants, respectively. At 100 mg of grazoprevir once daily, the mean maximum reductions in HCV RNA from baseline were 4.74 and 2.64 log10 IU/mL for GT1- and GT3-infected participants. Implications The results in the elbasvir monotherapy study showed that 10 to 50 mg of elbasvir was associated with a rapid decline in HCV viral load; the results in the grazoprevir monotherapy study suggest that doses of 50 mg of grazoprevir and higher are on the maximum response plateau of the dose–response curve for GT1-infected participants. The results of these proof-of-concept studies provided preliminary data for the selection of the dosages of elbasvir and grazoprevir to test in Phase II and III clinical studies. ClinicalTrials.gov identifiers: NCT00998985 (Protocol 5172-004) and NCT01532973 (Protocol 8742-002).