A 35-year-old woman with vivax malaria is treated with chloroquine and primaquine. Which pharmacological feature best distinguishes primaquine from chloroquine in the context of malaria treatment?

## Primaquine vs. Chloroquine: Pharmacological Distinction ### Target Stage and Mechanism **Key Point:** The fundamental distinction between primaquine and chloroquine lies in their **stage-specific activity** against the malaria parasite lifecycle. | Feature | Chloroquine | Primaquine | |---------|-------------|----------| | **Primary target** | Erythrocytic schizonts | Hypnozoites (liver) & gametocytes | | **Mechanism** | Inhibits hemozoin formation | Generates reactive oxygen species; uncouples oxidative phosphorylation | | **Clinical use** | Acute attack suppression | Radical cure (relapse prevention) | | **Parasite stage** | Blood stage | Pre-erythrocytic (hypnozoites) | | **Dosing** | Daily for 3 days | Daily for 14 days (or 8 mg/kg weekly for 8 weeks) | | **Relapse prevention** | No | Yes (for *P. vivax* and *P. ovale*) | ### Why Primaquine Prevents Relapse 1. **Hypnozoite Elimination:** Primaquine is the **only antimalarial** that can kill dormant hypnozoites in hepatocytes 2. **Mechanism:** Primaquine is metabolized to active metabolites that generate oxidative stress in hypnozoites, causing their destruction 3. **Clinical Outcome:** Without primaquine, *P. vivax* and *P. ovale* relapse in 50–80% of untreated patients **High-Yield:** Primaquine is **essential and irreplaceable** for radical cure of *P. vivax* and *P. ovale* malaria. No other antimalarial can eliminate hypnozoites. ### Clinical Pearl In India, where *P. vivax* is endemic, the combination of chloroquine (acute attack) + primaquine (radical cure) remains the standard regimen for vivax malaria in G6PD-normal patients. Failure to give primaquine results in relapses at 2–3 week intervals. **Warning:** Primaquine causes hemolysis in G6PD-deficient patients. Screening for G6PD deficiency is **mandatory** before primaquine administration. ## Mnemonic **PRIME:** **P**rimaquine = **P**re-erythrocytic (hypnozoites) + **R**adical cure + **I**rreplaceable for relapse + **M**etabolized to active form + **E**ssential for vivax/ovale