EFFECT OF COLD-TEMPERATURE STORAGE ON STABILITY OF BENZYLPENICILLIN RESIDUES IN PLASMA AND TISSUES OF FOOD-PRODUCING ANIMALS

A recently developed liquid chromatographic method is used to determine benzylpenicillin residues in incurred tissue and plasma samples from experimental animals stored at freezer temperatures of -20-degrees-C and -76-degrees-C. It was observed that penicillin-incurred plasma samples stored at -20-degrees-C for 2 months were relatively stable, showing a gradual loss of only 10-20% of the residues present at the beginning of the storage period. Loss of penicillin residues from bovine kidney and liver stored at -20-degrees-C occurred at a rate that was more rapid than from plasma. Losses in benzylpenicillin concentrations of up to 20% were observed in kidney and liver samples stored at -20-degrees-C after as little as 1 0 days of storage. Gluteal muscle samples stored at the same temperature showed almost 50% reduction in benzylpenicillin concentration after only 1 0 days of storage. However, incurred tissue samples stored at -76-degrees-C remained stable. The depletion of benzylpenicillin residues from edible tissues and biological fluids follows a first-order rate law.