A 28-year-old woman from Jharkhand is diagnosed with *Plasmodium vivax* malaria (parasitaemia 0.8%) on day 2 of fever. She is started on chloroquine 600 mg base stat, then 300 mg at 6 hours, 24 hours, and 48 hours. On day 10, she remains fever-free and asymptomatic. What is the most appropriate next step to prevent relapse?

Explanation

## Clinical Context The patient has *P. vivax* malaria with clinical cure (fever-free by day 10 after chloroquine). However, *P. vivax* and *P. ovale* have hypnozoites (dormant liver stages) that can cause relapses weeks to months after the initial attack if not eradicated. ## Radical Cure Strategy **High-Yield:** Primaquine is the only antimalarial that eliminates hypnozoites and prevents relapse in *P. vivax* and *P. ovale* malaria. Standard dose is 0.5 mg/kg/day for 14 days. G6PD deficiency screening is mandatory before primaquine to avoid haemolytic anaemia [cite:Harrison 21e Ch 219]. **Key Point:** Chloroquine kills erythrocytic schizonts (clinical cure) but does NOT eliminate hypnozoites. Without primaquine, relapse occurs in 40–50% of *P. vivax* cases within 3–12 months. **Clinical Pearl:** G6PD deficiency is common in malaria-endemic regions (Africa, Mediterranean, Southeast Asia, India). Primaquine causes acute haemolysis in G6PD-deficient patients. Variants of G6PD deficiency exist: - **Class II/III (African variant):** Mild haemolysis; primaquine 0.5 mg/kg/day × 14 days is safe. - **Class I (Mediterranean/Asian variant):** Severe haemolysis; primaquine contraindicated or requires dose reduction (0.75 mg/kg weekly × 8 weeks). **Mnemonic: PQ = Primaquine for Quiet hypnozoites** — Primaquine eradicates dormant liver parasites. ## Management Algorithm ```mermaid flowchart TD A["P. vivax or P. ovale malaria"]:::outcome --> B["Chloroquine for acute attack"]:::action B --> C{"Clinical cure achieved?"}:::decision C -->|Yes| D["Check G6PD status"]:::action D --> E{"G6PD normal?"}:::decision E -->|Yes| F["Primaquine 0.5 mg/kg/day × 14 days"]:::action E -->|No - Mild deficiency| G["Primaquine 0.5 mg/kg/day × 14 days with monitoring"]:::action E -->|No - Severe deficiency| H["Primaquine 0.75 mg/kg weekly × 8 weeks OR defer"]:::action F --> I["Relapse prevention"]:::outcome G --> I H --> I C -->|No| J["Repeat chloroquine or switch to artemisinin"]:::action ``` **Warning:** Do NOT give primaquine without G6PD testing. Do NOT use primaquine in pregnancy (teratogenic risk) — defer until postpartum.