Proguanil (proguanil hydrochloride) is a prophylactic antimalarial drug, which works by stopping the malaria parasite, Plasmodium falciparum, from reproducing once it is in the red blood cells. It does this by inhibiting the enzyme, dihydrofolate reductase, which is involved in the reproduction of the parasite.

Proguanil is usually taken in combination with another anti-malarial drug such as atovaquone (e.g., in the drug Malarone) or chloroquine. Malarone has fewer side effects than mefloquine, but can be more expensive because it's taken daily.

External Reference

Dihydrofolate reductase inhibitors | Antimalarial agents

Proguanil