The pharmacokinetics and relative bioavailability of two different formulated injectable gentamicin products were examined i.m. in 12 healthy young Chinese men at intervals of 1 week in a randomized cross-over design. Serum concentrations of gentamicin were measured by a fluorescence polarization immunoassay (FPIA) method sensitive to 0.01 μg/ml. The urine concentration of gentamicin was measured by the USP bioassay method. The serum protein binding of gentamicin was determined by an ultracentrifuge method and the free drug concentration was also determined by FPIA. No differences were found in bioavailability between gentamicin products of two manufacturers (Schering and Veterans). However, longer half-life, larger volume of distribution, slower distribution rate and much higher percentage of gentamicin excreted in the urine were observed in Chinese subjects than in Caucasians. Despite the longer half-life which was observed in Chinese, the total body clearance of the antibiotic in Chinese was about the same as that of Caucasians, therefore, the same gentamicin dosage may be needed for Chinese to achieve the desired serum level.
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