Excretion of penicillins and cephalexin in bovine milk following intramammary administration.

The elimination into bovine milk of beta-lactam antibiotic residues (procaine penicillin G, cloxacillin, ampicillin, oxacillin, cephalexin) following intramammary administration of 10 preparations marketed in France was studied. The quantitative analysis of residues was carried out by a microbiological agar diffusion method using Bacillus stearothermophilus. Sensitivity ranged from 0.001 I.U./ml for procaine penicillin G and 0.001 micrograms/ml for ampicillin to 0.02 micrograms/ml for cephalexin. The mean periods of elimination on which withholding times are based were between four and seven milkings according to the drugs administered.