Tilmicosin antibacterial activity and pharmacokinetics in cows

Area of Science:

• Veterinary Pharmacology
• Bacteriology
• Animal Health

Background:

• Bovine mastitis remains a significant challenge in dairy production.
• Antimicrobial resistance necessitates evaluation of existing drugs like tilmicosin.
• Understanding tilmicosin's efficacy and pharmacokinetics is crucial for its judicious use.

Purpose of the Study:

• To determine the in vitro susceptibility of bovine udder pathogens to tilmicosin.
• To evaluate the pharmacokinetics and safety of tilmicosin following intravenous and subcutaneous administration in cows.
• To assess tilmicosin concentrations in bovine udder secretions after subcutaneous administration.

Main Methods:

• Minimal inhibitory concentrations (MICs) were determined for Staphylococcus aureus and other Gram-positive pathogens.
• Tilmicosin pharmacokinetics were studied after intravenous and subcutaneous injections in cows.
• Udder secretion concentrations were measured microbiologically after subcutaneous dosing.

Main Results:

• Tilmicosin demonstrated potent activity against Staphylococcus aureus and other Gram-positive udder pathogens (MICs < 0.78-3.12 µg/mL).
• Intravenous administration showed rapid elimination (half-life 46.4-72.8 min), while subcutaneous administration yielded a longer half-life (4.18 h) and 22% bioavailability.
• High concentrations of tilmicosin (> 0.78 µg/mL) were detected in udder secretions for 8-9 days post-subcutaneous administration, with no systemic side effects observed.

Conclusions:

• Tilmicosin exhibits significant in vitro efficacy against key bovine mastitis pathogens.
• Subcutaneous administration in cows results in sustained drug levels in udder secretions, suggesting therapeutic potential.
• Tilmicosin demonstrates a favorable safety profile and pharmacokinetic characteristics for treating bovine udder infections.