Monitoring of benzylpenicillin decomposition in gastric contents by capillary zone electrophoresis

A method has been developed to follow the decay of the antibiotic penicillin, specifically penicillin G or benzylpenicillin, in the gastric contents of laboratory rats. Purification by centrifugation and DEAE cellulose treatment of the stomach contents (diluted with pH 9 phosphate-borate buffer) was sufficient to allow the quantification of penicillin by capillary zone electrophoresis. An internal standard was used to minimize the injection error. The loss of activity was greater in fasted animals, as expected from the lower pH of their gastric contents, than in fed rats. The in vivo kinetics of the decomposition of the antibiotic was compared to that obtained in water and in hydrochloric acid solutions.