Which drug is primarily used for the treatment or prophylaxis of malaria?

Chloroquine is primarily used for the treatment and prophylaxis of malaria because it is effective against the blood stages of the malaria parasite, specifically Plasmodium falciparum and Plasmodium vivax. The drug works by interfering with the parasite's ability to metabolize hemoglobin, which is critical for its survival. Chloroquine has been a cornerstone of malaria treatment for many years due to its efficacy, availability, and relatively low cost.

While other drugs, such as quinine, artemisinin, and pyrimethamine, also play roles in malaria management, they tend to serve different purposes or have specific contexts for use. Quinine is often used for more severe cases or when patients cannot tolerate chloroquine. Artemisinin derivatives are typically used for rapid treatment of severe malaria, particularly in combination therapies. Pyrimethamine is primarily used in the treatment of toxoplasmosis and as part of combination therapies for malaria but is not the first choice for prophylaxis. Thus, chlorquine's unique profile makes it the go-to medication for both treatment and prevention of malaria.