Stability of ivermectin in rumen fluids

Area of Science:

• Veterinary Pharmacology
• Ruminant Metabolism
• Parasitology

Background:

• Ivermectin is a widely used antiparasitic drug in livestock.
• Understanding drug metabolism in the rumen is crucial for drug efficacy and environmental impact assessment.
• Previous studies on avermectin metabolism have focused on liver microsomes and in vivo conditions.

Purpose of the Study:

• To investigate the in vitro metabolism of ivermectin in rumen fluid from sheep and cattle.
• To determine if ivermectin is broken down by rumen microbes.
• To explore potential reasons for ivermectin disappearance from rumen fluid.

Main Methods:

• In vitro incubation of tritium-labelled ivermectin (H2B1a component) in sheep and cattle rumen fluid at 38°C for 24 hours.
• Confirmation of microbial activity using [14C]cellulose conversion to 14CO2.
• Analysis of ivermectin disappearance and potential metabolite formation.

Main Results:

• No detectable metabolism of ivermectin occurred in vitro over 24 hours.
• Rumen microbes were viable, as evidenced by significant cellulose conversion to CO2.
• Disappearance of ivermectin from rumen fluid was likely due to binding to solids or surfaces.

Conclusions:

• Ivermectin is not metabolized by rumen microorganisms.
• Observed disappearance of ivermectin in vitro is attributed to non-metabolic processes like binding.
• Apparent effects on dung beetles are unlikely due to volatile ivermectin metabolites.