A 32-year-old woman from rural Odisha presents with fever, chills, and jaundice after returning from a malaria-endemic area. Blood smear confirms P. vivax infection. She is counselled about relapse risk. Which feature best distinguishes primaquine from chloroquine in preventing relapses?

Explanation

## Primaquine vs. Chloroquine: Relapse Prevention ### Role in Malaria Treatment | Feature | Primaquine | Chloroquine | |---------|-----------|-------------| | **Target stage** | Hypnozoites (liver) | Erythrocytic schizonts (RBC) | | **Prevents relapse?** | Yes (P. vivax, P. ovale) | No | | **G6PD screening required** | **Yes** (mandatory) | No | | **Haemolytic risk** | **High** (in G6PD deficiency) | Absent | | **Pregnancy safety** | Contraindicated (1st trimester) | Relatively safe | ### Key Point: G6PD Deficiency & Primaquine Haemolysis **High-Yield:** Primaquine is an **8-aminoquinoline** that generates oxidative stress in RBCs. In patients with **G6PD deficiency**, this leads to: - Acute haemolytic anaemia - Dark urine (haemoglobinuria) - Jaundice - Potential fatal outcome if unrecognized **Mnemonic:** **PRIM** = **Primaquine Requires Immediate Monitoring** (of G6PD status and haemoglobin) ### Clinical Pearl Chloroquine alone **cannot prevent relapse** in P. vivax and P. ovale because it does not kill hypnozoites dormant in hepatocytes. Primaquine is the **only agent** that eradicates hypnozoites and prevents relapse. However, **G6PD screening is mandatory** before primaquine use in endemic regions (India, Africa, Mediterranean, Southeast Asia) where G6PD deficiency prevalence is high [cite:Harrison 21e Ch 218]. ### Dosing in G6PD Deficiency If G6PD deficiency is confirmed: - Standard dose: 15 mg base daily × 14 days → **contraindicated** - Reduced dose: 45 mg base weekly × 8 weeks (primaquine phosphate 52.6 mg weekly) → safer alternative - Severe deficiency: primaquine avoided entirely; chloroquine alone + close monitoring ### Why Chloroquine Alone Fails Chloroquine kills the **asexual erythrocytic forms** (schizonts) but cannot reach hypnozoites sequestered in hepatocytes. Relapses occur 2–3 weeks after chloroquine monotherapy due to hypnozoite activation.