A phase I, randomized, open-label study of the multiple-dose pharmacokinetics of vemurafenib in patients with BRAF V600E mutation-positive metastatic melanoma

This study characterized the multiple-dose pharmacokinetics of vemurafenib 240-960 mg twice daily (bid) in BRAF (V600E) mutation-positive metastatic melanoma patients, using the commercial formulation (240-mg microprecipitated bulk powder film-coated tablets). Melanoma patients (N = 52) were randomly allocated to four vemurafenib dose cohorts (240, 480, 720, or 960 mg bid for 14 days). After the day 15 morning dose, doses were interrupted until day 22, at which point patients were restarted on vemurafenib. Serial pharmacokinetic samples were collected after the morning dose on days 1, 9, and 15; trough pharmacokinetic samples were collected on day 2. Vemurafenib concentration increased with multiple doses to steady state at day 15; C (max), AUC(0-8h), and AUC(0-168h) increased between 3.3- and 3.8-fold across the fourfold dose range tested. Statistical analysis indicated dose proportionality across the dose range of 240-960 mg bid. Day 15 mean accumulation ratios (ratio of AUC(0-8h) on day 15/AUC(0-8h) on day 1) ranged from similar to 19 to 25 across cohorts. At steady state, the peak-to-trough ratio for vemurafenib exhibited a relatively flat concentration-time profile throughout the bid dosing interval. During dose interruption (days 15-22), mean vemurafenib trough concentrations decreased to minimal levels; vemurafenib exhibited a mean terminal phase half-life of 31.5-38.4 h. Vemurafenib plasma concentration accumulates with multiple bid doses of 240 mg. Vemurafenib exposure (AUC and C (max)) is dose proportional over the 240- to 960-mg bid dose range and exhibits constant drug levels over the bid dosing interval.