Pharmacotherapeutic group: Antibacterials for systemic use, beta- lactam antibacterials, penicillins.
ATCvet code: QJ01CE90
Pharmacodynamic properties
The active substance, penethamate hydriodide, is a prodrug which releases benzylpenicillin. Chemically, it is a diethylaminoethanol ester of penicillin.
Mode of action:
Benzylpenicillin works by blocking the biosynthesis of the bacterial cell wall. Benzylpenicillin covalently attaches to and subsequently inactivates penicillin-binding proteins (PBPs), which are located on the inner surface of the bacterial membrane. The PBPs (transpeptidase, carbopeptidasas, endopeptidases) are enzymes involved in the terminal stages of bacterial cell-wall synthesis. Penicillins are only active against bacteria in the multiplication phase.
The antimicrobial spectrum of the active substance corresponds to that of benzylpenicillin which is effective against beta-lactamase negative Streptococcus agalactiae, Streptococcus dysgalactiae, Streptococcus uberis and Staphylococcus aureus.
Mechanisms of resistance:
The most frequent mechanism is producing beta-lactamases (more specifically penicillinase especially in S. aureus), which break the beta-lactam ring of penicillins making them inactive.
Pharmacokinetic particulars
Following intramuscular administration to dairy cows, Cmax is rapidly achieved in blood and milk (3 and 7 hours respectively). Ninety percent of the antibiotic is hydrolysed in blood and 98% in milk. As a result of hydrolysis, diethylaminoethanol and benzylpenicillin are produced, with the latter being the therapeutically active molecule. The distribution is rapid within the organism, with particular affinity for lung and mammary gland tissues. It crosses the placenta and enters the foetal circulation slowly.