Concentrations of methicillin in blood, normal milk and mastitic milk of cows after intramuscular injection of methicillin and tamethicillin.
Tamethicillin (TAM) is a basic ester pro-drug of methicillin (MET) which is converted in the body by non-specific esterases to MET. Equal doses of MET and TAM were administered intramuscularly in a crossover trial involving four dairy cows. Acute mastitis was induced in each cow by infusing two quarters of the udder with Escherichia coli endotoxin 3 h before antibiotic administration. Peak serum MET concentrations after MET injection were significantly (P less than 0.001) higher than peak serum drug concentrations after TAM injection. The t1/2 of MET in serum after MET and TAM treatments were 18 min and 2 h, respectively. Normal milk MET concentrations during the first 8 h after TAM administration were significantly (P less than 0.05) higher than after MET treatment. Mastitic milk MET concentrations during the period 2-6 after MET injection were significantly (P less than 0.01) higher than after TAM administration. However, MET concentrations which were equal to or higher than the minimal inhibitory concentrations for penicillin G-resistant staphylococci were maintained in the mastitic milk for 8 h after treatment with MET and TAM.
D000818:Animals; D002417:Cattle; D005260:Female; D007273:Injections, Intramuscular / Q000662:veterinary; D008414:Mastitis, Bovine / Q000097:blood / Q000188:drug therapy*; D008712:Methicillin / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000032:analysis; D008892:Milk / Q000032:analysis
C022165:tamethicillin; D008712:Methicillin