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Atovaquone for Veterinary Use

by Barbara Forney, VMD

Basic Information

Atovaquone is a broad-spectrum, antiprotozoal drug. Its mechanism of action is via inhibition of the parasite's mitochondrial electron transport. Atovaquone is used in human medicine in combination with azithromycin to treat Babesia microti infection. It has a favorable safety profile and appears to have fewer reports of adverse reactions than some of the previous treatments for Babesia. Atovaquone also is used in human medicine as an anti-malarial drug in the combination drug Malarone®.

Dogs and Cats

Atovaquone in combination with azithromycin is a promising new treatment for Babesia gibsoni in dogs. Babesia is a protozoal parasite of mammalian red blood cells and it is an emerging disease in many parts of the world. B. gibsoni infections are now widely endemic in the United States. There are two forms of Babesia that may infect dogs: the large Babesia (2-4 x 4-7m) and the small Babesia (1.1-2 x 1.2-4m). B. gibsoni is a small Babesia, as is Babesia microti, the protozoal species that infects humans.

The majority of cases of B. gibsoni found in the United States are in the Bull Terrier population or in dogs that have been bitten by or have fought with a Bull Terrier. Natural vectors for B. gibsoni are ixodid ticks and the brown dog tick Rhipicephalus sanguineus. Vertical transmission of B. gibsoni also may occur, as an infection has been found in a dam and her three-day-old pups. Clinical infections are most frequent in young animals.

B. gibsoni infections have been hard to treat and have not responded well to previous anti-babesial drugs, such as imidocarb diproprionate. Although controlled studies have not been published, the combination of atovaquone with azithromycin may improve the recovery rate and is thought to produce fewer adverse reactions. One author states that 50% of treated animals become PCR negative in six weeks.

Atovaquone combined with azithromycin also is used to treat Cytauxzoon felis. C. felis is a serious tick-borne protozoal disease of cats. Although there are no controlled studies yet, preliminary work using atovaquone and azithromycin suggest an improved survival rate of >60%. The success rate for treatment of C. felis with imidocarb was reported at 0-50%.

Atovaquone Side Effects

No information was found in the literature on the side effects of the atovaquone and azithromycin combination in animals. Malarone (atovaquone combined with proguanil hydrochloride) should not be used in dogs due to a high incidence of gastrointestinal side effects.

In humans, the most commonly reported side effects to the drug combination of atovaquone and azithromycin were diarrhea and rash and the most commonly reported side effects to Malarone were related to the digestive tract. They included abdominal pain, nausea, vomiting, anorexia and diarrhea.


No information was found in the literature regarding specific precautions for atovaquone in dogs or cats.

Drug Interactions

No information was found in the literature regarding drug interactions for atovaquone.


No information was found in the literature regarding overdose.

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Therapeutic Class
Anti-protozoal drug

Dogs and cats

May Be Prescribed by Vets for:
Dogs: Babesia gibsoni

Cats: Cytauxzoon felis.

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About the Author

Dr. Barbara Forney

Barbara Forney, VMD

Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.

She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.

Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.