## Drug of Choice for Acute Plasmodium vivax Malaria **Key Point:** Chloroquine remains the first-line agent for acute P. vivax malaria in India, despite emerging resistance in some endemic regions. ### Mechanism of Action Chloroquine is a 4-aminoquinoline that accumulates in the parasitophorous vacuole and inhibits haem polymerization, leading to toxic free haem accumulation and parasite death. ### Clinical Use in P. vivax - **Acute attack suppression:** Chloroquine eliminates erythrocytic schizonts (blood forms) - **Dosing:** 600 mg base on day 1, then 300 mg on days 2–3 (total 1500 mg base over 3 days) - **Efficacy:** Rapid fever clearance (48–72 hours) and parasite clearance ### Post-Treatment Relapse Prevention After chloroquine course, primaquine MUST follow to eliminate hypnozoites from the liver: - **Primaquine dosing:** 15 mg base daily for 14 days - **Timing:** Start after chloroquine course is complete - **G6PD screening:** Mandatory before primaquine (risk of haemolysis) **High-Yield:** The two-drug regimen (chloroquine + primaquine) is essential for P. vivax and P. ovale to prevent relapses; chloroquine alone will NOT prevent relapse. ### Comparison with Other Options | Drug | Role | Indication | |------|------|------------| | Chloroquine | First-line for acute attack | All P. vivax acute malaria | | Primaquine | Hypnozoiticide (liver) | Relapse prevention (post-chloroquine) | | Artemether | Artemisinin derivative | Severe malaria, cerebral malaria, P. falciparum | | Quinine | Older agent | Reserved for severe cases or resistance | **Clinical Pearl:** In this case, Schüffner's stippling and ring forms are pathognomonic for P. vivax. Chloroquine is the standard first-line drug; primaquine will be added after the acute phase to prevent relapse.
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