Rapid high-pressure liquid chromatographic method for analysis of phenoxymethylpenicillin in human serum

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Abstract
A selective high-pressure liquid chromatographic method for the determination of phenoxymethylpenicillin in human serum is described. The technique is based on the single extraction of the drug from acidified serum with diethyl ether. Chloramphenicol is used as internal standard. The chromatographic system consists of a reversed-phase C-18 column; the mobile phase is acetonitrile-0.01 M potassium acetate buffer (20:80 [vol/vol]; pH 6.5). The method can accurately measure serum penicillin concentrations down to 30 micrograms/liter with 500 microliter of sample. The coefficient of variation for intraassay variability of penicillin is between 1.5 and 4.9% in the range of 0.125 to 16.00 mg/liter. The extraction efficiency is 78.5 +/- 6.8% (+/- standard deviation; n = 9), and the calibration graph is linear in the concentration range studied. Pharmacokinetic data, obtained with the present method from seven healthy volunteers, are presented.