Atovaquone

BRAND NAMES

Mepron – primarily used for Pneumocystis jirovecii pneumonia (PCP) treatment and prophylaxis. 

Malarone – a combination of Atovaquone and Proguanil, used for malaria prevention and treatment

MECHANISM OF ACTION

Atovaquone works by inhibiting the cytochrome bc1 complex in the mitochondrial electron transport chain of target pathogens. This blockage disrupts mitochondrial membrane potential, reducing ATP production and nucleic acid synthesis, which halts pathogen growth. Its selective action on microbial mitochondria, rather than human cells, allows it to effectively treat infections such as malaria and Pneumocystis pneumonia.

PHARMACOKINETICS

Absorption

Atovaquone is poorly absorbed from the gastrointestinal tract when taken orally, with bioavailability ranging from 23% to 47% under fasting conditions. Its absorption is significantly enhanced when taken with high-fat meals, which can increase plasma concentrations up to two- to threefold. Because of its lipophilic nature, Atovaquone requires dietary fat to improve solubility and systemic uptake, making meal timing important for optimal therapeutic effect.

Distribution

Atovaquone is highly lipophilic and extensively binds to plasma proteins (≥99%), which limits its free circulating concentration. It distributes widely in the body tissues, particularly in lungs, liver, and kidneys, but penetrates the cerebrospinal fluid poorly. Its high protein binding and tissue accumulation contribute to sustained therapeutic levels in target organs.

Metabolism

Atovaquone undergoes minimal hepatic metabolism. It is largely excreted unchanged in the feces, with only a small fraction metabolized by the liver. Because it is not extensively metabolized, Atovaquone has limited drug-drug interactions compared with other antimicrobial agents.

Elimination

Atovaquone is primarily eliminated unchanged in the feces, with minimal renal excretion. Its elimination is slow, resulting in a long half-life of approximately 2–3 days, which supports once- or twice-daily dosing. Because it is not extensively metabolized, dose adjustments are generally not required for mild to moderate liver dysfunction, though severe hepatic impairment may affect drug levels.

PHARMACODYNAMICS

Atovaquone works by inhibiting the cytochrome bc1 complex in pathogen mitochondria, disruptingATP production and nucleic acid synthesis. This selective action suppresses the growth of organisms like Plasmodium spp. and Pneumocystis jirovecii, allowing effective treatment at therapeutic doses.

ADMINISTRATION

Atovaquone is given orally, usually as a tablet or suspension, and should be taken with food or a high-fat meal to improve absorption. Dosing varies by indication, typically twice daily for Pneumocystis pneumonia and once daily in combination therapy for malaria. The tablets should be swallowed whole to ensure proper uptake.

DOSAGE AND STRENGTH

Atovaquone is available in tablets (750 mg) and oral suspension (100 mg/mL). For Pneumocystis pneumonia treatment, the usual adult dose is 750 mg twice daily for 21 days. For Pneumocystis pneumonia prophylaxis, the dose is 750 mg once daily. In malaria prevention or treatment (as Malarone, combined with proguanil), dosing depends on age and weight, typically one or two tablets once daily for adults. Pediatric doses are calculated based on body weight according to standard guidelines.

DRUG INTERACTIONS

Atovaquone absorption can be reduced by antacids or acid-reducing drugs. Rifampin and some antibiotics may lower its levels, while it can increase effects of drugs like warfarin. Monitoring or dose adjustment may be needed.

FOOD INTERACTIONS

Atovaquone absorption is significantly improved when taken with high-fat meals. Taking it on an empty stomach can reduce bioavailability by up to 50%, potentially decreasing its effectiveness. Foods low in fat may not provide the same benefit, so a meal containing dairy, oils, or other fats is recommended with each dose.

CONTRAINDICATIONS

Atovaquone is contraindicated in patients with a known hypersensitivity to atovaquone or any component of the formulation. It should not be used in individuals with severe hepatic impairment without careful monitoring, and caution is advised in pregnancy unless the potential benefits outweigh risks. Use in neonates or infants under the recommended age should be avoided unless specifically directed by a healthcare provider.

SIDE EFFECTS

• Nausea

• Vomiting

• Diarrhea

• Abdominal pain

• Headache

• Rash

• Fever (less common)

• Insomnia (less common)

• Mouth ulcers (less common)

• Elevated liver enzymes (less common)

• Rare severe reactions: allergic reactions or hepatotoxicity

TOXICITY

Atovaquone is generally well tolerated, and toxicity is rare at therapeutic doses. High doses could potentially cause liver enzyme elevations or worsen preexisting hepatic dysfunction. There is no specific antidote, so management is supportive care, including hydration and monitoring of liver function.