Malason is a combination of two medicines: Pyrimethamine and Sulphadoxine which treat malaria. Pyrimethamine is an antiparasitic medicine which works by increasing the levels of haeme in the blood, a substance toxic to the malarial parasite. This kills the parasite and stops the infection from spreading. Sulphadoxine is an antibiotic which stops the bacteria from producing folic acid, a nutrient required for bacterial multiplication.