Atovaquone is a chemical compound that belongs to the class of naphthoquinones. Atovaquone is a hydroxy-1,4-naphthoquinone, an analog of ubiquinone, with antipneumocystic activity. It is manufactured in the US in the liquid form, or oral suspension, under the brand name Mepron. Trimethoprim-sulfamethoxazole (TMP-SMX, Bactrim) is generally considered first-line therapy for PCP or toxoplasmosis. However, atovaquone may be used in patients who cannot tolerate, or are allergic to, TMP-SMX. In addition, atovaquone has the advantage of not causing myelosuppression, which is an important issue in patients who have undergone bone marrow transplantation. Atovaquone, as a combination preparation with proguanil, has been commercially available from GlaxoSmithKline since 2000 as Malarone for the treatment and prevention of malaria.