Determination of ampicillin in human plasma by solid-phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS/MS) and its use in bioequivalence studies

A simple, fast, sensitive and selective solid-phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS/MS) method for the quantitative analysis of ampicillin (CAS 69-53-4) in human plasma was developed using amoxicillin as internal standard, and sample extraction by solid-phase extraction (SPE). Extracts were separated by reversed-phase C-18 with aqueous mobile phase (acetonitrile, 80:20, v/v) with 0.1% formic acid. The method was validated and successfully applied in a bioequivalence study of capsules 500 mg of ampicillin. Using a short running time of 2.5 min, the lower limit of quantification (LLOQ) for obtained ampicillin was 0.1 mu g/ml for a plasma sample of 250 pi and a recovery of 94.38% +/- 4.05. Bioequivalence between the products was determined by calculating 90% confidence intervals (CI) for the ratio of C-max AUC(0-t) and AUC(0-inf) values for the test and reference products, which were within the 0.80-1.25 interval proposed by FDA and EMEA. It is concluded that the two formulations are bioequivalent in their rate and extent of absorption, and thus, may be used interchangeably.