Safety, tolerability and pharmacokinetics of TAS-108, a novel anti-oestrogen, in healthy post-menopausal Japanese women: a phase I single oral dose study.

TAS-108 is a novel steroidal anti-oestrogen, expected to be useful for the treatment of breast cancer. The present study was conducted to investigate the safety, tolerability and pharmacokinetics of TAS-108 following the administration at a single oral dose of 40 mg to up to 120 mg in 12 post-menopausal women and the effect of food on the pharmacokinetics of the drug. All adverse events were mild and involved transient symptoms that resolved without therapeutic intervention. TAS-108 was readily absorbed and plasma levels of TAS-108 steadily declined, apparently in a multi-exponential manner. C(max) and AUC(0-12) were proportionally increased with increasing dose of TAS-108. The C(max) and AUC(0-t) of TAS-108 and its metabolite, deEt-TAS-108, were significantly increased to approximately 150% when TAS-108 was administered after a meal. Food did not affect the elimination half-life of TAS-108 or its metabolites. In this escalating dose-study of TAS-108, the drug was well tolerated by healthy post-menopausal Japanese women. The pharmacokinetics of TAS-108 indicated dose proportionality, and its bioavailability was significantly increased by food intake.