- Primaquine is the only medication effective against the hypnozoite form of Plasmodium vivax that resides dormant in the liver.
- This dormant stage causes relapses weeks to months after the initial infection.
- While chloroquine and other blood schizonticides clear the blood-stage parasites, they do not eliminate hypnozoites.
- Therefore, primaquine is essential for radical cure and prevention of relapse by targeting liver stages.
- Its use must be carefully considered in patients with G6PD deficiency due to the risk of hemolysis.

Reference: Davidson’s Principles and Practice of Medicine, 24th Edition, Chapter: Malaria, Page 1032.