AIMSThe aim of this phase 1, single centre, open label study in four patients with solid tumours was to determine the absolute bioavailability of a 2 mg oral dose of trametinib. Trametinib is an orally bioavailable, reversible and selective allosteric inhibitor of MEK1 and MEK2 activation and kinase activity. METHODSA microtracer study approach, in which a 5 μg radiolabelled i.v. microdose of trametinib was given concomitantly with an unlabelled 2 mg oral tablet formulation, was used to recover i.v. and oral pharmacokinetic parameters, simultaneously. RESULTSThe least-squares mean (90% confidence interval) absolute bioavailability of trametinib (2 mg tablet) was 72.3% (50.0%, 104.6%). Median tmax after oral administration was 1.5 h and the geometric mean terminal half-life was 11 days. The geometric mean clearance and volume of distribution after i.v. administration were 3.21 l h −1 and 976 l, respectively, resulting in a terminal elimination half-life of 11 days. CONCLUSIONSTrametinib absolute bioavailability was moderate to high, whereas first pass metabolism was low. WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Following oral dosing of 2 mg trametinib, median tmax was 1.5 h and the mean effective half-life (t1/2) was approximately 4 days. Trametinib is greater than 95% protein bound. Trametinib accumulates about six-fold with repeat daily dosing, and the concentration-time profiles showed a flat profile at steady-state with a low peak : trough ratio.• The absolute bioavailability of trametinib has not been previously reported.• The microtracer approach has been used previously to recover i.v. and oral pharmacokinetic parameters, simultaneously, which are used to estimate absolute bioavailability.• Determination of absolute bioavailability improves our understanding of the clinical pharmacology of a compound. WHAT THIS STUDY ADDS• Trametinib has moderate to high bioavailability (72.3%) following oral administration of a 2 mg tablet.• The i.v. microtracer study approach revealed the contribution of high oral bioavailability with low first pass metabolism and a prolonged terminal elimination phase to the pharmacokinetics of trametinib.

1. This study assessed the mass balance, metabolism and disposition of [(14)C]trametinib, a first-in-class mitogen-activated extracellular signal-related kinase (MEK) inhibitor, as an open-label, single solution dose (2 mg, 2.9 MBq [79 µCi]) in two male subjects with advanced cancer. 2. Trametinib absorption was rapid. Excretion was primarily via feces (∼81% of excreted dose); minor route was urinary (∼19% of excreted dose). The primary metabolic elimination route was deacetylation alone or in combination with hydroxylation. Circulating drug-related component profiles (composed of parent with metabolites) were similar to those found in elimination together with N-glucuronide of deacetylation product. Metabolite analysis was only possible from <50% of administered dose; therefore, percent of excreted dose (defined as fraction of percent of administered dose recovery over total dose recovered in excreta) was used to assess the relative importance of excretion and metabolite routes. The long elimination half-life (∼10 days) favoring sustained targeted activity was important in permitting trametinib to be the first MEK inhibitor with clinical activity in late stage clinical studies. 3. This study exemplifies the challenges and adaptability needed to understand the metabolism and disposition of an anticancer agent, like trametinib, with both low exposure and a long elimination half-life.

The aim of this study was to estimate the effect of a high-fat, high-calorie meal on the single-dose pharmacokinetics (PK) of trametinib, a MEK inhibitor. The design of this 2 treatment, 2 period crossover, incomplete wash-out study was influenced by the subject population, long half-life and PK variability; 24 subjects were randomized to a single, oral 2 mg trametinib dose administered in a fed/fasted state, followed by 7 days of serial PK sampling. Period 2 PK parameters were adjusted based on residual Period 1 concentrations. Geometric least square mean ratios of fed:fasted were 0.30, 0.76, and 0.90 for corrected maximum concentration (C(max)), area under concentration-time curve from time 0 to last quantifiable sample (AUC(0-last)) and AUC from time 0 extrapolated to infinity (AUC(0-α)), respectively. Median half-life was 6.3 and 5.3 days for fed and fasted regimens, respectively. Uncorrected PK parameters were consistent with these results. Food delayed absorption and had a mean difference in time of maximum concentration (t(max)) of 3.9 hours. Both oral trametinib doses were well-tolerated. Single-dose trametinib administration with food decreased the rate and, to a lesser degree, the extent of absorption, supporting the recommendation to administer trametinib 1 hour before or 2 hours after a meal.