Pyrantel pamoate resistance in horses receiving daily administration of pyrantel tartrate.

This research focuses on the efficacy of the anthelmintic (anti-parasitic) drugs pyrantel tartrate and pyrantel pamoate in controlling cyathostomes, a type of parasitic worm, in horses. The study suggests monitoring horses for resistance to pyrantel pamoate before using pyrantel tartrate and regularly checking for fecal worm egg counts before and after treatment periods.

Study Overview and Preliminary Results

• The study was conducted on 16 horses that were treated daily with an anthelmintic called pyrantel tartrate as part of a prophylactic (preventive) treatment against parasitic worm infection.
• Fecal worm egg counts (FWECs) were taken from all horses to assess the level of worm infection. The mean FWEC was found to be 478 eggs/gram of feces. However, only three horses were responsible for 85% of the total fecal egg output for the whole herd on the day of sampling.
• Six horses had low FWECs of fewer than 200 eggs/gram, and three horses that had recently arrived at the farm had even lower FWECs of fewer than 100 eggs/gram.

Fecal Worm Egg Count Reduction Test

• The day after initial FWECs were obtained, an FWEC reduction test was done in which horses with an FWEC greater than 100 eggs/gram (9 of the 16 horses) were treated with another anthelmintic, pyrantel pamoate.
• FWECs were repeated 14 days after the treatment with pyrantel pamoate, during which period the horses also continued their daily pyrantel tartrate treatment.
• The FWEC reduction, i.e., the difference in the FWEC before and after both treatments, was calculated for each of the 9 horses.
• The mean FWEC reduction for all these horses was 28.5%. The range of results varied from an increase of 21% in FWECs 14 days after treatment to a decrease of 100% in FWEC 14 days after treatment.

Study Conclusions and Recommendations

• The results indicate that some horses might have developed resistance to pyrantel pamoate, as shown by the small average decrease in FWECs and the fact that some horses even showed an increase.
• Thus, the study suggests that farms should check for resistance to pyrantel pamoate before using pyrantel tartrate as a preventive treatment against worm infection.
• Regular FWEC checks are also recommended before and after treatment to ensure efficacy of worm control measures, as resistance can develop over time and render the treatment ineffective.