Drug Monograph
Full clinical overview, indications, dosage references & safety notes.
Overview
Atovaquone (Mepron®) is an oral antiprotozoal agent used in dogs and cats for the treatment of selected protozoal infections. Its clinical use in veterinary medicine is limited but expanding, particularly in cases where standard therapies are ineffective or not tolerated.
In dogs, atovaquone is most commonly used in combination with azithromycin for the treatment of Babesia gibsoni infections, especially the Asian genotype. When used alone, it is considered a second-line option for pneumocystosis, following failure or intolerance of potentiated sulfonamides.
In cats, atovaquone in combination with azithromycin is recommended for the treatment of cytauxzoonosis caused by Cytauxzoon felis. This combination has been associated with improved survival when used as part of an aggressive, multimodal treatment protocol.
Mechanism of Action (MOA): Atovaquone is a hydroxynaphthoquinone compound that interferes with protozoal mitochondrial electron transport by targeting cytochrome b. This selectively inhibits energy production and de novo pyrimidine synthesis in susceptible protozoa, leading to impaired replication and survival. Mutations in protozoal cytochrome b may reduce drug susceptibility and contribute to treatment failure or relapse.
Atovaquone is not effective against bacterial, viral, or fungal infections. It is generally well tolerated in dogs and cats based on limited clinical experience, but careful adherence to dosing protocols and administration with food is essential to optimize absorption and therapeutic response.
Indications
Atovaquone is used in dogs and cats for the treatment of specific protozoal infections, primarily as part of combination therapy. Its use is generally reserved for cases where standard first-line treatments are ineffective, contraindicated, or not tolerated.
- Babesia gibsoni infection (dogs): Used in combination with azithromycin for the treatment of Babesia gibsoni infections, particularly the Asian genotype. This protocol is most effective in non-immunosuppressed dogs and is commonly selected for cases with relapse or resistance to other antiprotozoal therapies.
- Pneumocystosis (dogs): Used as a second-line treatment option when potentiated sulfonamides are ineffective or cannot be used. Atovaquone may be administered as a single agent in these cases.
- Cytauxzoonosis (cats): Recommended in combination with azithromycin for the treatment of infections caused by Cytauxzoon felis. This combination is considered part of an aggressive treatment protocol aimed at improving survival.
Dosage (Reference)
Dog
In dogs, atovaquone is used extra-label for specific protozoal infections. Administration with a fatty meal is essential to significantly enhance oral absorption and improve therapeutic response.
| Indication | Route | Dose | Notes |
|---|---|---|---|
| Babesia gibsoni (Asian genotype), B. conradae, B. vulpes | PO |
Atovaquone 13.3 mg/kg every 8 hours + Azithromycin 10 mg/kg every 24 hours |
Give with a fatty meal for optimal absorption. Duration: 10 days. Reserve immunosuppressive therapy for cases not responding within 3–5 days. |
| Babesia gibsoni (Asian genotype) | PO |
Atovaquone 17–25 mg/kg + Proguanil 7–10 mg/kg |
Combination product (Malarone®). Administer every 12 hours with a fatty meal for 10 days. May be combined with doxycycline 5 mg/kg PO every 12 hours for 30 days. |
| Pneumocystosis | PO | 15 mg/kg every 24 hours |
Used as second-line therapy. Duration: 3 weeks. |
• Always administer with food high in fat to enhance absorption.
• Relapse may occur, especially with single-agent therapy.
• Monitor clinical response and consider follow-up PCR testing when appropriate.
Cat
In cats, atovaquone is used extra-label in combination therapy for cytauxzoonosis. Aggressive supportive care and ensuring adequate food intake are critical to treatment success.
| Indication | Route | Dose | Notes |
|---|---|---|---|
| Cytauxzoonosis (Cytauxzoon felis) | PO |
Atovaquone 15 mg/kg every 8 hours + Azithromycin 10 mg/kg every 24 hours |
Duration: 10 days. Administer with food to maximize absorption. IV fluids and supportive care are typically required. |
• Consider placement of a feeding tube to reduce stress and ensure adequate food intake.
• Adequate nutritional support is essential to maximize drug absorption.
• Close monitoring is required throughout treatment.
Warnings & Precautions
Clinical experience with atovaquone in dogs and cats is limited. Although the drug appears to be generally well tolerated, careful patient selection, appropriate administration, and close monitoring are recommended to minimize the risk of therapeutic failure or adverse effects.
- Administration with food: Oral absorption of atovaquone is significantly enhanced when given with food, particularly meals high in fat. Animals that cannot eat or have poor appetite may achieve subtherapeutic drug concentrations.
- Malabsorption syndromes: Dogs or cats with gastrointestinal disease or malabsorption may have reduced drug absorption; alternative therapies should be considered in these patients.
- Limited veterinary safety data: Use in dogs and cats has been limited, and the full adverse effect profile is not well established; monitor patients closely during therapy.
- Resistance development: Mutations in protozoal cytochrome b may reduce susceptibility to atovaquone, particularly during treatment of Babesia gibsoni in dogs; relapse or treatment failure may occur.
- Combination therapy: For most indications, atovaquone should be used in combination with other agents (e.g., azithromycin) to improve efficacy and reduce the likelihood of resistance.
- Hypersensitivity: Although not reported in dogs or cats, discontinue therapy if signs suggestive of hypersensitivity (e.g., rash, acute gastrointestinal signs) develop.
- Pregnancy and lactation: Safety has not been established in pregnant or nursing animals; use only when the potential benefits to the dam outweigh the potential risks to offspring.
- Overdose risk: Toxic doses have not been established in dogs or cats; use caution to avoid dosing errors, especially with concentrated oral suspensions.
Drug Interactions
Clinically relevant drug interactions with atovaquone in dogs and cats are primarily related to its high plasma protein binding and factors that reduce gastrointestinal absorption. When used concurrently with the following medications, careful assessment and additional monitoring may be required.
- Highly protein-bound drugs (e.g., azole antifungals, furosemide, NSAIDs): Atovaquone is approximately 99.9% protein bound and may theoretically displace other highly bound drugs, leading to transient increases in free drug concentrations. These interactions are unlikely to be clinically significant but monitor for adverse effects.
- Metoclopramide: May decrease plasma concentrations of atovaquone by reducing gastrointestinal transit time; use concurrently only when no suitable alternatives are available.
- Rifampin: Can significantly decrease atovaquone plasma concentrations; concurrent use is not recommended due to the risk of treatment failure.
- Tetracyclines: May reduce atovaquone plasma concentrations; monitor clinical response if used together.
Side Effects & Overdose
Side Effects
Clinical use of atovaquone in dogs and cats has been limited, and the full adverse effect profile is not well defined. Based on available veterinary reports, the drug appears to be generally well tolerated when administered appropriately.
- Gastrointestinal upset: Vomiting may occur in dogs, particularly when using combination products containing atovaquone and proguanil. Nausea or diarrhea is possible but not well documented in veterinary patients.
- Dermatologic reactions: Skin rashes have not been commonly reported in dogs or cats, but should be considered possible; discontinue therapy if suspected.
- Limited adverse effect data: In a small study of dogs treated with atovaquone and azithromycin for Babesia gibsoni, no adverse effects were observed.
Overdose
Information regarding overdose or acute toxicity of atovaquone in dogs and cats is very limited. Minimum toxic doses have not been established for veterinary species.
- Expected signs: Based on human and laboratory data, overdose may result in gastrointestinal signs, central nervous system depression, or other nonspecific clinical abnormalities.
- Management: Treatment is supportive and symptomatic, guided by the animal’s clinical condition.
- Monitoring: Close observation and supportive care are recommended for animals with suspected overdose.
Key Notes
Practical clinical considerations to optimize the use of atovaquone in dogs and cats, focusing on points not emphasized elsewhere:
- Extra-label use: All veterinary uses of atovaquone in dogs and cats are extra-label; informed owner consent and appropriate documentation are recommended.
- Relapse monitoring: Clinical improvement does not always indicate complete parasite clearance, particularly in canine babesiosis; follow-up testing may be needed in cases of relapse.
- Variable response: Treatment response may vary between individual patients, even when standard protocols are followed.
- Stress reduction: Minimizing handling stress during treatment, especially in cats with cytauxzoonosis, may improve overall patient stability.
- Supportive care importance: Drug therapy alone is often insufficient; overall outcome depends heavily on concurrent supportive and nursing care.
- Client communication: Owners should be advised that side effects in dogs and cats are not fully characterized and to report any unexpected changes promptly.
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