Disposition of parathion after dermal application in pigs

Area of Science:

• Veterinary Pharmacology
• Toxicology
• Dermal Absorption Studies

Background:

• Organophosphorus insecticides are widely used in pour-on preparations for ectoparasite control in livestock.
• Understanding the pharmacokinetic behavior of these compounds after dermal application is crucial for assessing efficacy and safety.

Purpose of the Study:

• To investigate the pharmacokinetic parameters of parathion in pigs following intravenous and dermal administration.
• To determine the absorption, distribution, metabolism, and excretion profile of parathion and its metabolites after dermal exposure.

Main Methods:

• Pharmacokinetic analysis of parathion in pigs using both intravenous (i.v.) and dermal administration routes.
• Utilized unlabelled and radiolabeled (14C) parathion to track compound and metabolite concentrations over time.
• Non-compartmental analysis was applied to plasma concentration-time data.

Main Results:

• Intravenous administration yielded a mean residence time (MRT) of 2.15 h, body clearance (ClB) of 4.4 l/kg/h, and volume of distribution (Vss) of 9.8 l/kg.
• Dermal application resulted in a mean absorption time (MAT) of 78 h and a low bioavailability of 9.9%.
• 14C-parathion and its metabolites showed higher and more persistent plasma levels than parathion itself, with significant accumulation in the application site skin.

Conclusions:

• Dermal bioavailability of parathion in pigs is low, suggesting limited systemic absorption.
• The efficacy of pour-on organophosphorus insecticides likely relies on surface spreading rather than systemic distribution to reach ectoparasites.
• Further research into topical distribution mechanisms is warranted.