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

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 effects is needed.

Objectives: 1) Quantification of the effects of imidocarb dipropionate on equine orocaecal transit time (OCTT), with and without atropine or glycopyrrolate premedication and 2) investigation of an improved pretreatment 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 which will be ameliorated by premedication with either atropine or glycopyrrolate.

Methods: The effects of 3 drug therapies on OCTT were compared in 6 healthy horses in a randomised double-blind study vs. a saline control: 1) imidocarb dipropionate 2.4 mg/kg bwt administered intramuscularly (i.m.) with saline administered intravenously (i.v.; imidocarb/saline); 2) imidocarb dipropionate 2.4 mg/kg bwt administered i.m. with atropine 0.035 mg/kg bwt administered i.v. (imidocarb/atropine) and 3) imidocarb dipropionate 2.4 mg/kg bwt administered i.m. with glycopyrrolate 0.0025 mg/kg bwt administered i.v. (imidocarb/glycopyrrolate). The lactose 13C-ureide breath test was used to measure OCTT in each case and significance of treatment effect determined by a linear model analysis of variance.

Results: Imidocarb/atropine treatment caused an increase in OCTT (P < 0.05) whereas imidocarb/saline produced a nonsignificant decrease in OCTT. Imidocarb/saline caused colic and diarrhoea in 4 of 6 horses, which were not seen in any of the horses treated with imidocarb/atropine or imidocarb/glycopyrrolate or administered the saline control. Intestinal borborygmi were increased in imidocarb/saline and decreased in imidocarb/atropine treated horses, respectively.

Conclusions: Imidocarb/saline treatment induced colic signs and a potential reduction in OCTT while imidocarb/atropine treatment increased OCTT significantly when compared with imidocarb/saline. Both atropine and glycopyrrolate premedication ameliorated the clinical gastrointestinal effects of imidocarb but atropine produced significant inhibition of gastric and/or small intestinal motility not detected with glycopyrrolate. Premedication with glycopyrrolate is recommended when using imidocarb for treatment of equine piroplasmosis.