Primaquine: The Definitive Antimalarial for Radical Cure and Relapse Prevention
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Primaquine phosphate is an 8-aminoquinoline antimalarial agent with a unique and critical role in the management of Plasmodium vivax and Plasmodium ovale malaria. Unlike most other antimalarials that target the asexual blood stages of the parasite, Primaquine’s primary action is against the dormant hypnozoite forms residing in the liver. This makes it the only widely available medication for achieving a “radical cure”—preventing relapse from these specific species—and it also exhibits activity against gametocytes of Plasmodium falciparum, thereby reducing transmission. Its use represents a cornerstone in global malaria eradication efforts, though it requires careful patient selection and monitoring due to its potential for hemolytic anemia in individuals with glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Features
- Active Pharmaceutical Ingredient: Primaquine phosphate.
- Pharmacological Class: 8-Aminoquinoline antimalarial.
- Primary Mechanism of Action: Generates reactive oxygen species, disrupting the mitochondrial electron transport chain in plasmodia, leading to the elimination of hypnozoites and gametocytes.
- Available Formulations: Oral tablets (commonly 7.5 mg and 15 mg base equivalent).
- Prescription Status: Requires a prescription; not available over-the-counter.
Benefits
- Achieves a radical cure for P. vivax and P. ovale malaria by eliminating dormant liver-stage hypnozoites, preventing relapses that can occur months or even years after the initial infection.
- Significantly reduces the transmissibility of P. falciparum malaria by effectively clearing gametocytes from the bloodstream, interrupting the cycle of transmission.
- Provides a targeted therapeutic option that complements blood schizonticides like chloroquine or artemisinin-based combination therapies (ACTs).
- Offers a well-established safety and efficacy profile when used according to guidelines and with appropriate G6PD screening.
- Contributes directly to public health goals and malaria control programs by addressing the reservoir of infection that drives ongoing transmission.
Common use
Primaquine is indicated for two primary purposes:
- Radical Cure of P. vivax and P. ovale Malaria: This is its most critical use. It is administered following a course of a blood schizonticide (e.g., chloroquine or an ACT) that clears the acute, symptomatic blood-stage infection. Primaquine then targets the dormant hypnozoites in the liver to prevent future relapses.
- Transmission Blocking of P. falciparum Malaria: A single, lower dose of primaquine is used as a gametocytocide to eliminate the sexual stages of P. falciparum parasites. This does not treat the acute infection but reduces the patient’s ability to infect mosquitoes, thereby decreasing community transmission. This application is a key part of mass drug administration campaigns in elimination settings.
Dosage and direction
Dosing is weight-based and expressed in milligrams of primaquine base. G6PD status MUST be confirmed normal before initiating therapy for radical cure.
- Radical Cure (14-day regimen): The standard adult dose is 30 mg base (0.5 mg base/kg) orally once daily for 14 days. This is typically given concurrently with or immediately after the blood schizonticide course. Pediatric dosing is calculated as 0.5 mg base/kg once daily (max 30 mg) for 14 days.
- Transmission Blocking (single dose): A single dose of 45 mg (0.75 mg base/kg) is used for this indication.
- Administration: Tablets should be taken with food to minimize gastrointestinal upset. Adherence to the full prescribed course is absolutely essential for efficacy, especially for the 14-day radical cure regimen.
Precautions
- G6PD Testing Mandatory: Screening for G6PD deficiency is an absolute prerequisite before starting a radical cure course. Primaquine can cause severe hemolysis in G6PD-deficient individuals.
- Pregnancy: Contraindicated during pregnancy due to the unknown G6PD status of the fetus and risk of fetal hemolysis. Use in lactating women is only considered if the infant has been confirmed to have normal G6PD activity.
- Nicotinamide Adenine Dinucleotide (NADH) Methemoglobin Reductase Deficiency: Individuals with this condition are at increased risk of developing methemoglobinemia.
- Monitoring: Patients should be advised to monitor for and immediately report signs of hemolysis (e.g., dark urine, rapid heart rate, shortness of breath, fatigue) or cyanosis (signifying methemoglobinemia).
- Other Comorbidities: Use with caution in patients with pre-existing conditions that predispose them to hemolysis or in those with rheumatoid arthritis or lupus erythematosus (potential for exacerbation).
Contraindications
- Known glucose-6-phosphate dehydrogenase (G6PD) deficiency.
- Pregnancy.
- Breastfeeding, unless the infant has a documented normal G6PD level.
- Concomitant use with other medications known to cause hemolysis or depress the myeloid series of the bone marrow.
- History of a prior severe reaction to primaquine or other 8-aminoquinolines (e.g., tafenoquine).
Possible side effect
- Common: Abdominal cramps, nausea, vomiting, epigastric distress, chest pain.
- Serious (require immediate medical attention):
- Hemolytic Anemia: Manifested by dark urine (hemoglobinuria), jaundice (yellowing of skin/eyes), severe fatigue, tachycardia, and shortness of breath.
- Methemoglobinemia: Manifested by cyanosis (bluish/gray skin discoloration), chocolate-brown colored blood, headache, dizziness, fatigue, shortness of breath.
- Leukopenia: A decrease in white blood cell count.
- The risk and severity of hemolysis are directly related to the degree of G6PD deficiency and the dose of primaquine.
Drug interaction
- Other Hemolytic Drugs: Concurrent use with drugs like sulfonamides, nitrofurantoin, dapsone, or quinolones may increase the risk of hemolytic reactions.
- Myelosuppressive Agents: Drugs that suppress bone marrow function may compound the risk of leukopenia.
- Drugs Causing Methemoglobinemia: (e.g., nitrates, local anesthetics like benzocaine, dapsone) can have additive effects with primaquine.
Missed dose
If a dose is missed, it should be taken as soon as it is remembered on the same day. If it is not remembered until the next day, the patient should not double the dose but should simply resume the regular dosing schedule. Maintaining the 14-day course is critical; therefore, the course may need to be extended by one day to ensure 14 full doses are taken. Consult the prescribing physician for specific guidance.
Overdose
Symptoms of overdose are primarily an exaggeration of its known adverse effects: severe abdominal cramps, vomiting, burning epigastric distress, central nervous and cardiovascular disturbances, cyanosis (due to methemoglobinemia), and profound hemolytic anemia with methemoglobinemia in susceptible individuals. There is no specific antidote. Management is supportive and includes gastric lavage (if ingestion was recent), monitoring of hematocrit and blood gases, and treatment of methemoglobinemia with methylene blue if severe. Note: Methylene blue is itself contraindicated in G6PD-deficient patients.
Storage
Store at room temperature (20°C to 25°C or 68°F to 77°F), in a tight, light-resistant container. Keep out of reach of children and pets. Do not use after the expiration date printed on the packaging.
Disclaimer
This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author and publisher are not responsible for any specific health or allergy needs that may require medical supervision or for any adverse effects resulting from the use of the information contained herein.
Reviews
- “As an infectious disease specialist working in Southeast Asia, primaquine is an indispensable tool in our fight against vivax malaria. The 14-day regimen is a compliance challenge, but its efficacy in preventing relapse is unmatched. Universal G6PD screening is non-negotiable.” – Dr. A. Sharma, MD
- “The introduction of single-dose primaquine for gametocyte clearance in our falciparum elimination zone has had a measurable impact on local transmission rates. It’s a powerful public health intervention when used correctly.” – Public Health Official, Sub-Saharan Africa
- “Patient education is paramount. We spend considerable time explaining the importance of completing the full course and the signs of potential hemolysis. In G6PD-normal patients, it is generally well-tolerated.” – Clinical Pharmacist