Pharmacokinetics assessment of moxidectin long-acting formulation in cattle

Area of Science:

• Veterinary Pharmacology
• Pharmacokinetics
• Drug Disposition

Background:

• Moxidectin is a widely used antiparasitic agent in cattle.
• Understanding the pharmacokinetics of long-acting (LA) formulations is crucial for optimizing treatment efficacy and duration.
• Previous studies have primarily focused on injectable formulations, necessitating research into novel delivery systems.

Purpose of the Study:

• To characterize the plasma and hair disposition of moxidectin following subcutaneous administration of a 10% LA formulation in Charolais cattle.
• To determine key pharmacokinetic parameters, including Cmax, Tmax, MRT, and AUC, in both plasma and hair over a 120-day period.
• To compare the bioavailability of the LA formulation with existing injectable formulations.

Main Methods:

• Subcutaneous administration of moxidectin (1 mg/kg) LA formulation to five Charolais cattle.
• Serial blood and hair sampling for 120 days post-administration.
• Plasma extraction and derivatization followed by HPLC analysis with fluorescence detection for moxidectin quantification.
• Calculation of pharmacokinetic parameters (Cmax, Tmax, MRT, AUC).

Main Results:

• Moxidectin was detected in plasma within 1 hour and in hair within 2 days, with peak concentrations observed at approximately 3.4 days (plasma) and 2 days (hair).
• Mean residence time (MRT) was significantly longer in plasma (28.9 days) than in hair (13.3 days).
• The bioavailability of the LA formulation was comparable to the 0.2 mg/kg subcutaneous injectable formulation, despite a higher dose rate.

Conclusions:

• The 10% LA moxidectin formulation demonstrates prolonged absorption and distribution in cattle, with detectable concentrations in plasma and hair for up to 120 days.
• Moxidectin hair concentrations effectively reflect plasma disposition, suggesting hair analysis as a potential biomarker for drug exposure.
• The extended pharmacokinetic profile of the LA formulation supports its efficacy for sustained parasite control, warranting correlation with clinical efficacy studies.