The effect of carboxylesterase 1 (CES1) polymorphisms on the pharmacokinetics of oseltamivir in humans.

PURPOSE: The aim of this study was to examine whether carboxylesterase 1 (CES1A) genetic polymorphisms affect the pharmacokinetics of oseltamivir. METHODS: Thirty healthy Japanese male and female subjects ranging in age from 20 to 36 years voluntarily participated in this study. These subjects were administered a single 75-mg dose of oseltamivir (Tamiflu®), and blood samples were collected predose and up to 24 h after oseltamivir administration. Oseltamivir and its active metabolite, oseltamivir carboxylate, were measured by liquid chromatography-time of flight/mass spectrometry with solid-phase extraction. The CES1A diplotypes [a combination of haplotypes A (CES1A3-CES1A1), B (CES1A2-CES1A1), C (CES1A3-CES1A1variant), and D (CES1A2-CES1A1variant)] were determined by PCR-restriction fragment length polymorphism analysis and direct sequencing. RESULTS: All subjects completed the study according to the protocol, and no clinically meaningful adverse events were attributable to the administration of oseltamivir. No significant differences in the pharmacokinetic parameters of oseltamivir and oseltamivir carboxylate were observed according to CES1A genotype. In one subject, the peak concentration and area under the concentration-time curve (AUC) of oseltamivir were approximately tenfold higher than the mean values of the other subjects. CONCLUSIONS: In our study, the known interindividual variability in oseltamivir metabolism was not explained by CES1A genetic polymorphisms, but are likely the result of other factors. While one subject was found to exhibit an approximate tenfold higher AUC than the other subjects, no abnormal behaviors were associated with the increased oseltamivir plasma concentrations. Further studies are required to reveal the cause of individual differences in CES1A metabolism and the abnormal behavioral effects of oseltamivir.

Determination of celiprolol in human plasma using high performance liquid chromatography with fluorescence detection for clinical application.

A new method of analysis has been developed and validated for the determination of plasma celiprolol concentration. Plasma samples (1 ml) were pre-purified by solid-phase extraction with Bond Elut C18. The separation was achieved with XBridge C18 column (150 mm × 3.0mm i.d., 3.5 µm) at 35 °C using a mixture of acetonitrile and 10mM ammonium acetate buffer (pH 10.5) (34:66, v/v) under isocratic conditions at a flow rate of 0.4 ml/min. The peak was detected using a fluorescence detector at excitation 250 nm and emission 482 nm. Retention times for the internal standard (acebutolol) and celiprolol were 4.2 min and 6.3 min, respectively. Calibration curves were linear over the range of 1.0-1000 ng/ml (r>0.999), with a limit of quantification at 1.0 ng/ml. Intra- and inter-assay precision (relative standard deviation) were less than 13.3% and the accuracy (relative error) was -5.1% to 11.5% at four different concentrations. This proposed method was successfully applied to a study of pharmacokinetic interactions between celiprolol and apple juice in humans.