ATCvet Code: QJ01RA01

Penicillin G is a beta-lactam antibiotic and its structure contains the beta-lactam ring and thiazolidine ring common to all penicillins. Beta-lactam antibiotics prevent the bacterial cell wall of susceptible Gram-positive bacteria from forming by interfering with the final stage of peptidoglycan synthesis. They inhibit the activity of transpeptidase enzymes, which catalyse cross-linkage of the glycopeptide polymer units that form the cell wall. They exert a bactericidal action but cause lysis only of growing cells.

Dihydrostreptomycin is an aminoglycoside antibiotic active against gram-negative aerobes, which after penetration of the cell envelope binds to receptors on the 30S sub unit of the bacterial ribosome. It induces misreading of the genetic code on the messenger ribonucleic acid (mRNA) template, causing bacteriostasis. Aminoglycosides exert synergistic action in combination with beta-lactam antibiotics.

After injection of Pen & Strep, the procaine penicillin is rapidly absorbed from the site of injection, with maximum penicillin levels of between 1 and 2 µg/ml for horses, sheep and pigs and 0.5 µg/ml for cattle, being obtained within 2 hours of injection.

The penicillin elimination half-lives are approximately 2 hours for sheep and pigs, 5 hours for cattle and 11 hours for horses. Dihydrostreptomycin is absorbed at a similar rate, with maximum plasma levels of 23 µg/ml being obtained for cattle, sheep and pigs, and 15 µg/ml for horses. The elimination half-lives are approximately 2 hours for cattle, sheep and pigs and 4 hours for horses.