Atovaquone and Azithromycin for the Treatment of Cytauxzoon felis
ACVIM 2008
A.J. Birkenheuer1; L.A. Cohn2; M.G. Levy1; E.B. Breitschwerdt1; H.S. Marr1
1North Carolina State University-College of Veterinary Medicine, Raleigh, NC, USA 2University of Missouri-College of Veterinary Medicine, Columbia, MO, USA

Cytauxzoonosis is an emerging infectious disease of domestic cats in the United States. Historically Cytauxzoon felis was believed to be uniformly fatal in domestic cats. However, over the past decade there have been scattered reports of cats with and without anti-protozoal drug therapy surviving C. felis infections. Atovaquone and azithromycin has recently been demonstrated to be the most effective therapy for the treatment of canine babesiosis caused by Babesia gibsoni, and organism related to C. felis. The purpose of this study is to describe the survival rate of cats with cytauxzoonosis that were treated with atovaquone and azithromycin combination therapy.

Twenty-two cats from AR, NC and MO with naturally occurring cytauxzoonosis (infections confirmed by microscopy and/or polymerase chain reaction) were treated with atovaquone (15mg/kg PO TID) and azithromycin (10mg/kg PO Q24). Additional supportive care varied between cases, but all cases were treated with intravenous fluids and most with heparin. Sixty-four percent (14/22) of the cats survived to discharge and 36% (8/22) died or were euthanized. At least 6 of the cats that died did so within several hours of admission. Detailed clinical and laboratory data was not available for all cases. Long-term follow-up information was available for six cats and they all are alive and clinically normal at least 19 months after discharge. Each of the veterinarians that participated in treatment of cats for this study had prior experience in treatment of cytauxzoonosis with either supportive care alone or supportive care plus imidocarb dipropionate. Prior to the beginning of this study, survival of C. felis infected cats from their practices was a rare occurrence.

Survival of these cases cannot clearly be attributed to the anti-protozoal therapy, but atovaquone and azithromycin combination therapy appears to be a promising treatment option for cytauxzoonosis. Cats that survive cytauxzoonosis can have complete resolution of signs and excellent long-term prognosis. A controlled study comparing the efficacy of atovaquone and azithromycin to imidocarb dipropionate is ongoing.

Speaker Information
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Adam Birkenheuer, DVM, PhD, DACVIM
North Carolina State University
Raleigh, NC

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