Toxoplasmosis, atovaquone treatment

Two other agents show promise in treatment of ocular toxoplasmosis. Atovaquone, primarily used for mild to moderate episodes of Pneumocystis carinii pneumonia, has been effective in small series of patients with toxoplasmosis. It appears to have activity against both tachy-zoites and tissue cysts. More recent studies on atovaquone in toxoplasmosis are limited to murine models, and no further reports on this drug therapy in humans have been published. Azithromycin, a macrolide antibiotic, is efficacious against T. gondii and can also kill tissue cysts. A randomized study of 46 patients compared the combinations of azithromycin plus pyrimethamine versus pyrimethamine plus sulfadiazine in treatment of ocular toxoplasmosis efficacy was similar, but the azithromycin/ pyrimethamine regimen caused less adverse effects. 

Clinical Use. Atovaquone (Mepron) is used primarily to treat the protozoon that causes toxoplasmosis and the fungus that causes pneumocystis pneumonia in immunocompromised patients.6 This drug is not typically the primary treatment for pneumocystis, but is often reserved for patients who cannot tolerate more traditional treatments using sulfamethoxazole and trimethoprim (see Chapter 34) or pentamidine (see later). Atovaquone can also be used to prevent and treat resistant cases of malaria, and the antimalarial effects of this drug seem especially useful when combined with proguanil.48... 

When the CD4 count of this patient fell below 200/pL. prophylaxis against pneumocystis pneumonia was instituted. The currently recommended therapy is double-strength trimethoprim-sulfamethoxazole or dapsone. Alternative prophylactic regimens include aerosolic pentamidine, dapsone plus pyrimethamine, and atovaquone. Primary prophylaxis against toxoplasmosis is normally recommended with CD4 cell counts below 100/pL in AIDS patients who are IgG antibody-positive. Trimethoprim-sulfamethoxazole plus dapsone is also prophylactic against toxoplasmosis. With the continued decline in CD4 cells, exacerbation of candidal infection may occur despite use of clotrimazole troches, necessitating treatment with fluconazole or itraconazole. 

With as many as 70% of patients with AIDS developing pneumocystis and, of these, nearly 60% of the patients on cotrimoxazole developing serious side effects to this combination, atovaquone is an important alternative drug (16). Atovaquone also has been reported to be effective for the treatment of toxoplasmosis caused by Toxoplasma gondii, although it has not been approved for this use. 

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