Effect of 60Co-irradiation on penicillin G procaine in veterinary mastitis products

The effect of 60Co-irradiation on penicillin G procaine in a peanut oil-based veterinary mastitis product was examined by reversed-phase high-performance liquid chromatography (HPLC). The HPLC method is capable of separating and quantifying procaine, penicillin G, and various degradation compounds. Penicillin G recovery from a placebo formulation was 100.4% with a relative standard deviation of less than 1%. When irradiated at 4.0 Mrads, the penicillin G in two product lots decreased slightly (approximately 1-2%) with a corresponding increase in two compounds inherently present in bulk penicillin G powder. These compounds may be formed in abundance by treating penicillin G in an acidic solution. From the mass spectrometric analysis and the relative retention data with authentic compounds, these compounds were identified as benzylpenilloaldehyde and benzylpenaldic acid. Values obtained by the HPLC method on the product irradiated and stored at various temperatures correlated well with those of the microbiological assay. No significant decrease in the procaine was detected even after 4.0-Mrad irradiation. The HPLC method is applicable for analysis of other beta-lactam antibiotics.