Depletion of Penicillin G residues in milk of lactating buffaloes (Bubalus bubalis) after intramuscular administration: preliminary results

Penicillin G (PenG) is one of the most widely used antibiotic for the treatment of postpartum diseases in milk producing animals. The existing legislation on veterinary medicines requires that pharmacologically active substances authorized in cattle (Bos taurus) may also be targeted to buffaloes (Bubalus bubalis) with the same withdrawal periods, but in literature there are not studies on depletion of this β-lactam in buffalo milk. The purpose of this research was to investigate the persistence of PenG in milk of lactating buffaloes (n=six) treated with a combination product containing a soluction for intramuscular injection of procaine penicillin G (200,000 IU/mL) and dihydrostreptomycin sulfate (250 mg/mL) every 24 h for 3 days. Milk samples were collected twice daily up to milking 12 post-treatment (3 milkings more compared to bovine withdrawal period). A simple and reproducible method was developed for the extraction and PenG residues were detected by high performance liquid chromatography coupled to tandem mass spectrometry in positive ionization mode. The highest concentration of the antibiotic (275 μg/kg) was detected in the milk of the first milking post-treatment and the levels were below the maximum residue limit of 4 μg/kg, set by Regulation (EU) 37/2010 for PenG, in all treated buffaloes at milkings 12 post-treatment. These preliminary results seems to demonstrate that the depletion of PenG in lactating buffaloes is not similar to those reported in bovine species and that the milk of buffaloes treated with PenG during the lactating period is not compliant for dairy production after 9 milkings post treatment.