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Objective: S-1 is an oral anticancer agent combining tegafur (FT), a prodrug of 5-fluorouracil (5-FU), with potassium oxonate (oteracil) and gimeracil (CDHP) respectively to mitigate gastrointestinal toxicity and increase the half-life of 5-FU. This article presents a population pharmacokinetic analysis of these four compounds in Western cancer patients. The second objective was to compare the pharmacokinetics of S-1 in Western and Japanese patients. Methods: A single dose (25-45 mg/m²) of S-1 was administered to 60 patients. In each patient, 6 concentrations of FT, 5-FU, oteracil and CDHP were measured over 24hr. Using NONMEM, oteracil and CDHP were analyzed separately, and the individual estimates of CDHP parameters were included in the joint analysis of FT and 5-FU. We used validation techniques to assess differences between the two populations, and finally we compared the exposures in Western and Japanese patients using simulations. Results: A compartmental model describing the PK of the 4 compounds was developed The influence of CDHP on the elimination of 5-FU was well described by an enzymatic inhibition model. The model provided a good fit for all compounds. The pharmacokinetics for 5-FU and oteracil were similar between Western and Japanese patients, but apparent differences in exposure to 5-FU resulted from different total doses due to different body sizes. [ABSTRACT FROM AUTHOR]

Trastuzumab has transformed the treatment of HER2-positive breast cancer. Because of impending European patent expiry in 2017, numerous trastuzumab biosimilars are currently undergoing comparability exercises for marketing authorization. Although biosimilar products have been approved in Europe since 2006, many obstacles are expected for trastuzumab, resulting from its nature as a monoclonal antibody, its impact on overall survival, and its extensive biochemical complexities. Unsolved questions need to be addressed for the evaluation of biosimilars' activity in terms of appropriate clinical endpoint definitions for such anticancer drugs, specific assessment pathways and comparative testing of biosimilars, untested ensuing de facto combination of trastuzumab biosimilars with cytotoxics, and immunogenicity monitoring among immunocompromised patients. In such a context of uncertainties, the recent approval by the French parliament of biosimilar substitution, which would allow dispensing trastuzumab biosimilars in place of the originator, should interrogate the oncological community. A think tank of experts was created to delineate specificities and challenges stemming from trastuzumab biosimilars.