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Twice-daily dosing of RDZ no longer recommended for treatment of intestinal Tritrichomonas foetus infection

We would like to thank Xenoulis et al1 for their recent retrospective study in which information is provided on the outcome of cats that were treated with ronidazole for Tritrichomonas foetus infection. We agree with the authors’ recommendation of a treatment regimen for infections caused by T foetus of 30 mg/kg ronidazole (RDZ) q24h for 14 days.1 However, they reference a previous study of ours that recommended that cats that relapse should be treated with 30–50 mg/kg RDZ PO q12h.1,2 Based on our recent feline RDZ pharmacokinetic (PK) studies, we no longer recommend twice-daily dosing of RDZ.3 In our PK study, we determined that the half-life of RDZ is long (10.5 h), and that 48 h after a single dose of 30 mg/kg immediaterelease RDZ capsules orally there was still drug remaining in the cats’ plasma.3 Simulations based on our PK studies showed that twice-daily administration of 30 mg/kg RDZ PO would lead to drug accumulation.3 Neurotoxicity, including tremors, ataxia and agitation, is a reported and potentially dangerous side effect of RDZ in cats.4,5 As such, we no longer advocate twice-daily RDZ at this dose. However, it should also be noted that our PK studies did not assess the efficacy of our revised recommendations of once-daily 30 mg/kg RDZ administration for T foetus-infected cats. Such work remains to be done. We wanted to draw readers’ attention to these recent PK studies, so that cats are not inadvertently overdosed and risk neurologic sequelae based on outdated recommendations. References 1 Xenoulis PG, Lopinski DJ, Read SA, et al. Intestinal Tritrichomonas foetus infection in cats: a retrospective study of 104 cases. J Feline Med Surg 2013; 15: 1098–1103. 2 Gookin JL, Copple CN, Papich MG, et al. Efficacy of ronidazole for treatment of feline Tritrichomonas foetus infection. J Vet Intern Med 2006; 20: 536–543. 3 LeVine DN, Papich MG, Gookin JL, et al. Ronidazole pharmacokinetics after intravenous and oral immediaterelease capsule administration in healthy cats. J Feline Med Surg 2011; 13: 244–250. 4 Rosado TW, Specht A and Marks SL. Neurotoxicosis in four cats receiving ronidazole. J Vet Intern Med 2007; 21: 328–331. 5 Pham D. Chronic intermittent diarrhea in a 14-month-old Abyssinian cat. Can Vet J 2009; 50: 85–87.