Keywords14 C, absolute bioavailability, elimination route, mass balance, pimasertib
AIMThis trial (NCT: 01713036) investigated the absolute bioavailability, mass balance and metabolite profile of pimasertib in a new design combining these investigations in a single group of patients.
METHODSSix male patients with pathologically confirmed, locally advanced or metastatic solid tumours were enrolled. Exclusion criteria included Eastern Cooperative Oncology Group performance status >1. In Part A of the trial, patients received a 60 mg oral dose of unlabelled pimasertib followed by an intravenous (i.v.)
RESULTS
Following i.v. administration, [14 C]pimasertib exhibited a geometric mean total body clearance of 45.7 l h À1 (geometric coefficient of variation [geometric CV]: 47.2%) and a volume of distribution of 229 l (geometric CV: 42.0%). Absolute bioavailability was 73%. The majority of the oral [ 14 C] dose (85.1%) was recovered in excreta. Total radioactivity was mainly excreted into urine (52.8%) and faeces (30.7%) with 78.9% of the [ 14 C] dose recovered as metabolites. Two major circulating metabolites were identified in plasma: a carboxylic acid (M445) and a phosphoethanolamine conjugate (M554). The safety profile was in line with the published pimasertib trials.
CONCLUSIONPimasertib showed a favourable pharmacokinetic profile with high absolute bioavailability and a unique metabolic pathway (conjugation with phosphoethanolamine).
British Journal of Clinical Pharmacology
WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT• Pimasertib is a new selective, oral inhibitor of mitogen-activated protein kinases 1 and 2 (MEK1/2).• Comprehensive information about the pharmacokinetics, including absolute bioavailability, metabolism and elimination routes, of cancer drugs is often incomplete.
WHAT THIS STUDY ADDS• Description of a trial design combining investigation of absolute bioavailability and mass balance/metabolite identification in a single group of six male cancer patients.• Identification of a new metabolic pathway for drugs, i.e. conjugation with phosphoethanolamine.• Information about key pharmacokinetic parameters and the drug disposition of pimasertib in cancer patients.
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