The tick-borne protozoal disease equine piroplasmosis (EP) impacts horses worldwide, causing hemolytic anemia (the body's immune system attacks and kills its own red blood cells) and even death. Veterinarians' drug of choice for eliminating the causative parasites, Theileria equi and Babesia caballi, is imidocarb dipropionate, which is effective but commonly causes untoward side effects such as severe diarrhea and colic and, in rare cases, liver and kidney toxicity. Researchers in Scotland recently examined ways to minimize gastrointestinal complications when treating EP with this drug.
At the 2012 American Association of Equine Practitioners' (AAEP) Convention, held Dec 1-5 in Anaheim, Calif., Janina Kutscha, DrMedVet, BVSc (Hons), MRCVS, of Ardene House Veterinary Practice, in Aberdeen, Scotland, described this study, in which she and colleagues treated six horses with one of three once-weekly treatment protocols or a saline control.
To evaluate the drug's effects on the intestines, the team measured the elapsed time from ingestion to the drug reaching the cecum (orocecal transit time, or OCTT) using a stable, nonradioactive isotope breath test. She noted that OCTT is dependent on gastric emptying and small intestinal transit time. The test involves feeding an isotope-labeled, nonabsorbable carbohydrate to the horse, which passes through the stomach and intestine until it reaches the cecum. There, cecal microbes split the labeled substance and the isotope eventually appears in exhaled breath via bloodstream transfer to the lungs. Researchers evaluate isotopes collected from breath samples by using mass spectroscopy to calculate OCTT.
Kutscha explained that researchers premedicated the treatment group receiving intramuscular (IM) imidocarb with intravenous (IV) saline (I/S), IV atropine (I/A), or IV glycopyrrolate (I/G). They gave control horses IV and IM saline. She and colleagues collected breath samples and completed physical examinations at regular intervals before and after drug administration. In addition, they assessed each horse's specific vital signs, including heart rate, respiratory rate, mucous membrane color and capillary refill, and audible intestinal sounds. Of particular interest were the severity and duration of colic and diarrhea.
The I/S protocol caused severe colic and diarrhea, with increased gut sounds and respiratory rates lasting several hours. It had a minimal effect on the OCTT, said Kutscha, indicating that imidocarb exerted its primary action on the large colon--this resulted in abnormal intestinal motility that led to diarrhea and colic.
Researchers did not detect signs of colic in the I/A group, though they noted a significant increase in OCTT and a decrease in audible gut sounds indicating effects on both the small and large intestines. The heart rate remained elevated for a longer time than with glycopyrrolate premedication.
Horses in the I/G group displayed no colic signs, had OCTTs were similar to those of saline controls, and their audible gut sounds decreased only mildly; these findings indicated that, again, the drug's main effect was on the large colon. Kutscha and colleagues noted a smaller heart rate increase for a shorter duration than what they saw with the I/A protocol.
Kutscha and her colleagues determined that when targeting equine piroplasmosis using imidocarb, premedicating with glycopyrrolate prevents gastrointestinal side effects without delaying small intestinal transit. She emphasizes, "This ultimately improves the welfare of horses."
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.