(d) Quinine occurs naturally in the bark of the cinchona tree. For centuries, it was the only treatment for malaria. Quinine contains two weakly basic nitrogen atoms.Quinine remains an important antimalarial drug, almost 400 years after its effectiveness was first documented. However, its continued use is challenged by its poor tolerability, poor compliance with complex dosing regimens, and the availability of more efficacious antimalarial drugs.