Atovaquone
hydroxy-1,4-naphthoquinone
Also known as: Mepron · Malanil · Wellvone · BW-556C · Atovacuona · Atovakvoni · Atovaquonnum
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Babesia gibsoni (Asian genotype) infections | 13.3 mg/kg PO q8h | PO | q8h | 10 days | 🌎 NA |
| Pneumocystosis | 15 mg/kg PO once daily | PO | q24h | 3 weeks | 🌎 NA |
- Babesia gibsoni (Asian genotype) infections: Give with Azithromycin 10 mg/kg PO once daily. Reserve immunosuppressive therapy for cases that are not rapidly responding (3-5 days) to anti-protozoal therapy.
- Pneumocystosis: Considered second line therapy after potentiated sulfonamides.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Cytauxzoonosis (Cytauxzoon felis) | 15 mg/kg PO q8h | PO | q8h | Not specified | 🌎 NA |
- Cytauxzoonosis (Cytauxzoon felis): Give with azithromycin 10 mg/kg PO q24h. All cases were treated with IV fluids and most received heparin.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Atovaquone is a highly lipophilic, synthetic hydroxynaphthoquinone antiprotozoal agent. In veterinary medicine, it has revolutionized the treatment of specific, notoriously difficult-to-treat tick-borne protozoal infections.
Key Clinical Uses:
- Babesia gibsoni in Dogs: Used synergistically with azithromycin. B. gibsoni is a small piroplasm that is often refractory to traditional therapies like imidocarb dipropionate. The atovaquone/azithromycin combination is currently the treatment of choice.
- Cytauxzoon felis in Cats: Used in combination with azithromycin. Cytauxzoonosis is a highly fatal tick-borne disease in cats; this drug combination, alongside aggressive supportive care (IV fluids, heparin), has significantly improved survival rates.
- Pneumocystosis in Dogs: Serves as a second-line therapy for Pneumocystis pneumonia when potentiated sulfonamides (like trimethoprim-sulfa) cannot be used or are ineffective.
Clinical Pearl: Atovaquone is generally well-tolerated as a single agent or with azithromycin, but it is notoriously expensive. The human combination drug Malarone® (atovaquone/proguanil) should not be substituted in dogs, as the proguanil component causes severe gastrointestinal toxicity.
Mechanism of action
Atovaquone acts as a selective and potent inhibitor of the protozoan mitochondrial electron transport chain.
- It acts as a structural analogue of ubiquinone (Coenzyme Q).
- It binds to the ubiquinol oxidation pocket of the cytochrome bc1 complex (Complex III) in the protozoan inner mitochondrial membrane.
- This binding blocks electron transfer → collapses the mitochondrial membrane potential → halts the function of dihydroorotate dehydrogenase, an enzyme critically dependent on electron transport.
- Inhibition of this enzyme prevents de novo pyrimidine synthesis. Because these specific protozoa lack the ability to salvage preformed pyrimidines from their host, they cannot synthesize DNA or RNA, leading to parasite death.
Safety & warnings
Contraindications
- Patients with a known hypersensitivity to atovaquone
- Patients with severe malabsorption syndromes
- Patients who cannot tolerate oral intake or cannot take the drug with a high-fat meal
Adverse effects
- Gastrointestinal upset (nausea, vomiting, diarrhea)
- Rashes or hypersensitivity reactions
- Elevated liver enzymes
- CNS effects (headache, dizziness in humans)
- Fever
- Neutropenia and anemia (rare)
Precautions
Administration Warning: The drug is highly lipophilic and has poor bioavailability on an empty stomach. It must be administered with a high-fat meal to ensure adequate systemic absorption.
Toxicity Warning: Do not use the human combination product Malarone® (atovaquone and proguanil) in dogs due to severe gastrointestinal adverse effects associated with proguanil.
Pregnancy/Nursing: FDA Category C. Studies in rabbits showed increased maternal and fetal toxicity (decreased fetal growth, early resorption). Use during pregnancy only if the potential benefit justifies the risk. It is excreted in milk in rats, though it is unlikely to pose significant risk to nursing puppies.
Drug interactions
Can decrease atovaquone plasma concentrations
Can decrease atovaquone plasma concentrations
Can decrease atovaquone plasma concentrations
Monitoring
- Clinical signs of efficacy (resolution of fever, lethargy, anemia)
- Serial CBCs to monitor anemia and platelet counts
- BUN, liver enzymes, and serum potassium (hypokalemia) in severe cases
- PCR testing at 60 days and 90 days post-therapy to confirm 'clearing' of B. gibsoni
Pharmacokinetics
Absorption
Bioavailability is highly dependent on food. In humans, fasting bioavailability is 23-47%, but the presence of food (particularly high in fat) increases bioavailability significantly (2+ fold).
Distribution
Highly bound to plasma proteins (99.9%). Levels in the CSF are approximately 1% of those found in plasma.
Metabolism
There may be limited hepatic metabolism.
Elimination
The bulk of absorbed drug is eventually eliminated unchanged in the feces. Enterohepatic recycling occurs.
Overdose
Limited information is available for any species regarding acute toxicity. Minimum toxic doses have not been established; laboratory animals have tolerated massive doses up to 31.5 grams without lethal effect.
If an overdose occurs, treatment should be symptomatic and supportive. Due to high protein binding, dialysis is unlikely to be effective.
Available products
Formulations
- Oral suspension (150 mg/mL)
Human-labeled
- Atovaquone Oral Suspension: 150 mg/mL in 210 mL bottles; citrus flavor; Mepron® (GlaxoWellcome); (Rx)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
The commercially available oral suspension should be stored at room temperature (15-25°C) in tight containers and protected from bright light; do not freeze.
Client information
Important Administration Instructions:
- Give with a fatty meal: This medication must be given with food high in fat (e.g., a small amount of ice cream, tuna oil, butter, or meat fat) to be properly absorbed into your pet's body. Without fat, the drug will not work effectively.
- Shake well: Gently shake the bottle before drawing up each dose.
- Storage: Store the liquid at room temperature, away from bright light. Do not freeze it.
What to Watch For:
- This medication is generally well-tolerated, but because it is a newer therapy in veterinary medicine, we are still learning about all potential side effects.
- Contact your veterinarian immediately if your pet develops a skin rash, or experiences severe or persistent vomiting or diarrhea.
- Note: The liquid is bright yellow and can stain fabrics or surfaces, so handle it carefully.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.