Anti-malarial pill. Blisterpack of Malarone, an anti-malarial drug. Malaria is caused by the parasite Plasmodium sp., which is transmitted into the bloodstream by mosquito bites. Malarone is a combination drug, each tablet containing 250 milligrams of atovaquone and 100 milligrams of proguanil hydrochloride. The two active ingredients prevent the parasite Plasmodium falciparum, which causes the most serious form of malaria, malignant malaria, from reproducing in the bloodstream. Higher doses of the two active ingredients can also be used to treat less serious forms of malaria.