Equine piroplasmosis treatment protocols : specific effect on orocaecal transit time as measured by the lactose C-13-ureide breath test

Abstract

Reasons for performing study: Imidocarb dipropionate is the drug of choice for equine piroplasmosis, but its administration causes severe colic and diarrhoea. An imidocarb protocol that reduces these signs is required. Objectives: (1) Quantification of the effects of imidocarb dipropionate on equine orocaecal transit time (OCTT), with and without atropine or glycopyrrolate premedication; (2) Investigation of an improved pre-treatment regimen for imidocarb administration. Hypothesis: Treatment with imidocarb dipropionate will result in colic and reduced OCTT as demonstrated by the lactose 13C-ureide breath test (LUBT), which will be ameliorated by premedication with atropine or glycopyrrolate. Methods: The effects of three drug therapies on OCTT were compared in six healthy horses in a randomised double-blind study versus a saline control: (i) imidocarb dipropionate 2.4 mg/kg intramuscularly (IM) with intravenous saline (I/S); (ii) imidocarb dipropionate 2.4 mg/kg IM with atropine 0.035 mg/kg IV (I/A); (iii) imidocarb dipropionate 2.4 mg/kg IM with glycopyrrolate 0.0025 mg/kg IV (I/G). The LUBT was used to measure OCTT in each case, and significance of treatment effect determined by a linear model analysis of variance (ANOVA). Results: I/A treatment caused an increase in OCTT (P < 0.05), whereas I/S produced a non-significant decrease in OCTT. I/S caused colic and diarrhoea in four of six horses after injection, which was not seen in any horse with I/A or I/G treatments or saline control. Intestinal borborygmi were increased in I/S and decreased in I/A treated individuals respectively. Conclusions: I/S treatment induced colic signs and a potential reduction in OCTT, whilst I/A treatment increased OCTT significantly when compared to I/S. Both atropine and glycopyrrolate premedication ameliorated the clinical gastrointestinal effects of imidocarb, but atropine produced significant inhibition of gastric and/or small intestinal motility, which was not seen with glycopyrrolate. Pre-medication with glycopyrrolate is recommended when using imidocarb for equine piroplasmosis.