Proguanil, also known by its CAS number 500-92-5, is a pharmaceutical substance used for the prevention and treatment of malaria. It is a derivative of the antimalarial drug atovaquone. Proguanil functions as a prodrug, meaning it is metabolized in the body to its active form, cycloguanil, which inhibits the parasite’s ability to synthesize nucleic acids. This disruption ultimately leads to the death of the malaria parasite. Proguanil is available in various formulations, including tablets, which are commonly used for prophylaxis, and combination products with atovaquone for treatment. It is considered an essential medication for the prevention and management of malaria in many regions of the world.