1. Clinical Overview
Primaquine phosphate is an 8-aminoquinoline antimalarial agent, primarily used for the radical cure (prevention of relapse) of Plasmodium vivax and Plasmodium ovale malaria by eliminating dormant hypnozoites in the liver. It is also used for prophylaxis against malaria and, in a critical public health role in India, for the transmission-blocking 'gametocytocidal' activity against Plasmodium falciparum.
| Onset | Duration | Bioavailability |
|---|---|---|
| Rapidly absorbed; onset of action against gametocytes occurs within hours. Effect on hypnozoites is delayed, with full radical cure assessed over weeks to months post-treatment. | The therapeutic effect against hypnozoites is prolonged and considered curative after a standard course. It has a short plasma half-life, necessitating daily dosing. | Approximately 96% following oral administration. |
2. Mechanism of Action
Primaquine's exact mechanism is not fully elucidated. Its activity is believed to be mediated through the generation of reactive oxygen species (ROS) and interference with mitochondrial function in the parasite. It is uniquely effective against the dormant hypnozoite stages of P. vivax and P. ovale in the liver (radical cure). It also demonstrates potent activity against sexual-stage gametocytes of all Plasmodium species, thereby preventing transmission to mosquitoes.
3. Indications & Uses
- Radical cure (prevention of relapse) of Plasmodium vivax malaria
- Radical cure of Plasmodium ovale malaria
- Gametocytocidal activity against Plasmodium falciparum (for public health transmission blocking)
4. Dosage & Administration
Adult Dosage: For radical cure of P. vivax: 15 mg (0.25 mg/kg) base once daily for 14 days, taken with food. MUST be preceded by a blood schizonticide (e.g., Chloroquine or Artemisinin-based Combination Therapy) to treat the acute blood stage infection. For falciparum gametocytocidal activity (single dose): 45 mg (0.75 mg/kg) as a single dose.
Administration: Administer orally, once daily, with food to minimize gastrointestinal upset. The 14-day course must be completed in full for radical cure efficacy, even if the patient feels well. Do not crush or chew the tablet unless specified by the manufacturer.
5. Side Effects
Common side effects may include:
- Nausea
- Abdominal pain/cramps
- Vomiting
- Anorexia
- Headache
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Chloroquine | Increased plasma concentrations of primaquine; may increase toxicity risk. Administer sequentially, not concurrently. | Major |
| Other Hemolytic Drugs (e.g., Dapsone, Sulfonamides, Nitrofurantoin) | Increased risk of severe hemolytic anemia, especially in G6PD-deficient individuals. | Contraindicated |
| CYP2D6 Inhibitors (e.g., Fluoxetine, Paroxetine, Quinidine) | May reduce the formation of active metabolites, potentially decreasing primaquine efficacy. | Moderate |
| Mefloquine | Potential for increased risk of cardiotoxicity (QT prolongation). | Moderate |
| Warfarin | Primaquine may potentiate anticoagulant effect; monitor INR closely. | Moderate |
7. Patient Counselling
- DO complete the full 14-day course as prescribed, even if you feel better.
- DO take the tablet with food.
- DO inform all your doctors and pharmacists that you are taking primaquine.
- DO get the G6PD test done before starting treatment.
- DONT take the medicine if you are pregnant, planning pregnancy, or breastfeeding.
- DONT take it if you have not been tested for G6PD deficiency.
- DONT consume alcohol during the treatment course.
8. Toxicology & Storage
Overdose: Symptoms of overdose include severe abdominal cramps, vomiting, burning epigastric distress, central nervous system and cardiovascular disturbances (including cardiac arrhythmia, shock, convulsions, coma), cyanosis due to methemoglobinemia, and profound hemolytic anemia with acute renal failure.
Storage: Store below 30°C, protected from light and moisture. Keep in the original blister pack or container. Keep out of reach of children.