Simple, Economical, and Reproducible LC--MS Method for the Determination of Amoxicillin in Human Plasma and its Application to a Pharmacokinetic Study

A simple, economical, and reproducible high-performance liquid chromatography mass spectrometric (MS) method is developed and validated for the determination of amoxicillin in human plasma. The present method has been successfully used to determine bioequivalence between a test and innovator formulation of amoxicillin 500 mg capsules. The method is validated in terms of selectivity, precision/accuracy, recovery, dilution integrity, matrix effect, effect of anti-coagulant, and stability studies. Sample preparation is carried out by solid-phase extraction (HLB Oasis cartridges). The processed sample is chromatographed on Hypersil Gold (4.6 x 50 mm); 3 microm C18 column, using 10mM ammonium formate buffer (pH 5.0) and acetonitrile, (10:90, v/v) as mobile phase. Amoxicillin is detected by MS-MS detection with turbo-ion spray in positive ion mode. The weighed (1/X2) calibration curves were linear over the range of 0.17 to 17.0 microg/mL. The intra day precision is from 1.3% to 8.8% and intra day accuracy is 94.1% to 108.5%. The inter day precision is from 1.8% to 6.2% and inter-day accuracy is 95.1% to 105.9%. Mean recovery of 66.3% is observed for amoxicillin and 71.6% for internal standard (ampicillin). The stability of amoxicillin is studied at -15 degrees C and -50 degrees C using human plasma with different anti-coagulants (citrate, monobasic sodium phosphate, dextrose, and adenine-citrate, monobasic sodium phosphate, dextrose, and adenine and ethylene diamine tetraacetic acid-ethylene diamine tetraacetic acid). No significant degradation is observed for 60 days.