Atovaquone
Atovaquone is a hydroxynaphthoquinone antiprotozoal used in veterinary medicine mainly in combination with azithromycin for selected blood-borne protozoal infections. Important applications are Babesia gibsoni infection in dogs and Cytauxzoon felis infection in cats. It is highly lipophilic, and oral exposure is influenced by the formulation and feeding conditions.
Reduction of parasite burden and improvement in clinical disease do not guarantee sterilizing cure. Combination therapy, resistance and persistence of infection are therefore important to understanding its role, especially in animals that may remain carriers after recovery.
Group
Antiprotozoal hydroxynaphthoquinone
Mechanism of Action
Atovaquone is structurally related to ubiquinone and inhibits the protozoal mitochondrial cytochrome bc1 complex. Disruption of electron transport impairs maintenance of mitochondrial function and energy-related processes needed for parasite survival.
Interference with mitochondrial electron flow can also impair pathways linked to de novo pyrimidine synthesis, reducing the supply of precursors for nucleic-acid production in susceptible organisms. Selectivity reflects differences in the parasite target and metabolic dependence rather than a nonspecific toxic effect on every host cell.
Combination with azithromycin provides activity through an additional mechanism and can improve treatment response. Mutations affecting the mitochondrial target can reduce susceptibility, so apparent initial improvement does not prove that the infection has been eradicated or that retreatment with the same approach will always succeed.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Babesia gibsoni infection | 13–15 mg/kg | PO | Every 8 h | Up to 10 days; Do not use in: Pregnancy; Usually combined with azithromycin 10 mg/kg PO every 24 hours. Give with a high-fat meal. |
| Babesia gibsoni – exact combination course | 13.3 mg/kg | PO | Every 8 h | Up to 10 days; Do not use in: Pregnancy; Asian-genotype B. gibsoni; combine with azithromycin 10 mg/kg PO daily for 10 days and give with a fatty meal. Reserve immunosuppression for selected cases not responding within 3–5 days. |
| Pneumocystosis | 15 mg/kg | PO | Every 24 h | Up to 21 days; Second-line alternative after potentiated sulfonamides; give with food. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Cytauxzoon felis infection | 15 mg/kg | PO | Every 8 h | Do not use in: Pregnancy; Combine with azithromycin 10 mg/kg every 24 hours and give with a high-fat meal. Duration is not supplied. |
Indications
- Canine Babesia gibsoni infection in combination with azithromycin, using the supported species-specific protocol.
- Feline Cytauxzoon felis infection in combination with azithromycin and intensive supportive treatment appropriate to disease severity.
- Selected refractory protozoal disease only where supporting evidence identifies a susceptible organism; this is not a universal treatment for every Babesia species or hemoparasite.
- Control of clinical disease and reduction in parasitemia may occur without complete elimination, particularly in cytauxzoonosis, so recovered animals may retain infection.
Contraindications
- Avoid during pregnancy.
- Consider alternatives when malabsorption or inability to take food makes oral exposure unreliable.
- Known hypersensitivity.
Interactions
- Rifampin lowers exposure in people; animal interaction evidence is limited.
- Metoclopramide and tetracycline can reduce atovaquone exposure; most interaction evidence is human.
Adverse effects
- Proguanil-containing combinations can increase diarrhea in dogs.
- Human adverse effects include rash, cough and diarrhea; animal reports are limited.
Toxicity
Minimum toxic exposures are not established in veterinary patients. Treat overdose symptomatically and support hydration and gastrointestinal function.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Atovaquone oral suspension 750 mg per 5 mL | Oral Liquid | 750 mg / 5 mL | PO |
Monitoring and Administration
Give with a high-fat meal to improve absorption. Treatment experience and controlled evidence remain limited.
Store oral suspension at room temperature protected from light; do not freeze. Malarone also contains proguanil and is not equivalent to single-ingredient atovaquone.
Monitor serial CBC and clinical response in canine babesiosis; severe cases can develop renal or hepatic abnormalities and hypokalemia. A described organism-clearance assessment uses PCR at 60 and 90 days after treatment. Shake suspension gently and give with a fatty meal. Cytauxzoonosis requires supportive treatment in addition to antimicrobials.