Pharmacotherapeutic group: Beta lactamase sensitive penicillins.
ATCvet code: QJ01CE90
Pharmacodynamic properties
In aqueous solution penethamate is hydrolysed to form benzylpenicillin and diethylaminoethanol. The mode of action of benzylpenicillin is by prevention of cell wall synthesis during bacterial cell growth and its activity is primarily bactericidal. 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
Penethamate hydriodide is a prodrug which is hydrolysed to benzylpenicillin and diethylaminoethanol in aqueous solution. The pKa-value of penethamate hydriodide is 8.4. This means that in aqueous solution at physiological pH of 7.2, 8.2% of the drug will be present as the uncharged molecule while 91.8% will be present as the ion. After intramuscular injection, penethamate itself as well as the released alcohol, diethylaminoethanol, has not shown any unexpected pharmacological effects.
Following intramuscular injection of the product to cows the active ingredient is quickly absorbed and maximum serum concentrations are reached approximately 3 hours post treatment. Systemic elimination proceeds with a half-life of 3.5 hours and is virtually completed after 24 hours.