Monepantel-based anthelmintic combinations to optimize parasite control in cattle.

Area of Science:

• Veterinary Parasitology
• Pharmacology
• Livestock Health

Background:

• Anthelmintic resistance in gastrointestinal nematodes poses a significant threat to livestock production.
• Existing anthelmintics, including macrocyclic lactones (ML) and benzimidazoles (BZ), exhibit widespread resistance in cattle.
• There is a critical need for improved strategies to manage drug-resistant nematode infections in cattle.

Purpose of the Study:

• To evaluate the efficacy and pharmacokinetics of monepantel (MNP) alone and in combination with ML or BZ anthelmintics.
• To assess MNP's effectiveness against gastrointestinal nematodes resistant to ML and BZ in naturally infected calves.
• To determine the impact of co-administration on MNP's systemic exposure and its metabolite's availability.

Main Methods:

• Calves on two commercial farms were treated with MNP, ML (ivermectin, abamectin), BZ (ricobendazole, albendazole), or combinations.
• Efficacy was assessed by measuring fecal egg counts and nematode burdens.
• Pharmacokinetic studies involved analyzing plasma concentrations of MNP and its metabolite monepantel sulphone (MNPSO2) using HPLC.

Main Results:

• MNP alone demonstrated high efficacy (98-99%) against ML- and BZ-resistant nematodes, including Haemonchus, Cooperia, and Ostertagia species.
• Combined treatments of MNP with benzimidazoles (albendazole, ricobendazole) achieved 100% efficacy against all gastrointestinal nematode genera, including Oesophagostomum.
• Co-administration of MNP with ML or BZ anthelmintics decreased systemic exposure to the parent MNP drug but did not affect the availability of its primary metabolite, MNPSO2.

Conclusions:

• Oral monepantel is a highly effective treatment option for managing drug-resistant gastrointestinal nematode infections in cattle.
• Combining MNP with benzimidazole compounds offers a viable strategy to enhance efficacy, broaden the spectrum of activity, and potentially extend the lifespan of these anthelmintics.
• Combination therapy is recommended to overcome resistance and improve control of economically important nematode parasites in cattle.