Primaquine: The Definitive Antimalarial for Radical Cure
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Primaquine phosphate is an 8-aminoquinoline antimalarial agent with a unique and critical therapeutic role. It is the only medication widely available for the radical cure of Plasmodium vivax and Plasmodium ovale malaria, targeting the dormant hypnozoite forms of the parasite that reside in the liver. This action prevents relapse, a hallmark of these malaria species, which can occur weeks or even months after the initial illness. Its use is a cornerstone of public health strategies in endemic regions and for treating returning travelers, moving beyond mere symptom suppression to achieve a true biological cure.
Features
- Active Ingredient: Primaquine phosphate.
- Pharmacologic Class: 8-Aminoquinoline antimalarial.
- Mechanism of Action: Believed to generate reactive oxygen species that interfere with mitochondrial electron transport and pyrimidine biosynthesis in the Plasmodium parasite.
- Primary Indication: Radical cure (prevention of relapse) of P. vivax and P. ovale malaria.
- Secondary Indication: Terminal prophylaxis (for travelers leaving endemic areas) and primary prophylaxis (in specific, limited scenarios).
- Dosage Forms: Typically available as 7.5 mg and 15 mg base equivalent tablets.
- Prescription Status: Prescription-only medication requiring medical supervision.
Benefits
- Eradicates Dormant Liver Stages: Uniquely targets and eliminates the hypnozoite forms of P. vivax and P. ovale, preventing the cycles of relapse that characterize these infections.
- Achieves Definitive Cure: Moves beyond simply clearing the acute blood-stage infection (achieved by other drugs like chloroquine) to provide a complete biological cure, eliminating the parasite from the human host.
- Reduces Transmission: By clearing both blood and liver stages, it reduces the reservoir of infection within a community, contributing to malaria control and elimination efforts.
- Prevents Late-Onset Clinical Malaria: Protects individuals, particularly non-immune travelers, from experiencing a debilitating malarial relapse long after they have left an endemic area.
- Proven Efficacy: Has a long history of clinical use and is recommended by all major global health bodies, including the WHO and CDC, for this specific purpose.
- Generally Well-Tolerated: When prescribed appropriately to patients without contraindications, the standard course is completed without significant adverse events for the majority of individuals.
Common use
Primaquine is exclusively used for the prevention and treatment of malaria. Its most critical and common use is for the “radical cure” of malaria caused by Plasmodium vivax or Plasmodium ovale. This involves co-administration with a blood schizonticide (e.g., chloroquine or artemisinin-based combination therapy) to treat the acute blood infection, while primaquine acts on the dormant liver hypnozoites. It is also used for “terminal prophylaxis” (also called presumptive anti-relapse therapy) in individuals with significant exposure to P. vivax or P. ovale who are departing an endemic area, to eliminate any hypnozoites that may have been acquired but are not yet symptomatic. In rare cases, it may be used for primary prophylaxis.
Dosage and direction
Dosing is based on milligrams of primaquine base (not the salt). The standard regimen must be followed precisely under medical guidance.
- Radical Cure of P. vivax Malaria: The adult dose is 30 mg base (2 x 15 mg tablets) orally once daily for 14 days, taken concurrently with a blood schizonticide like chloroquine. Pediatric dosing is 0.5 mg base/kg/day (up to adult dose) for 14 days.
- Terminal Prophylaxis: 30 mg base orally once daily for 14 days after leaving the endemic area. Often started in the last 1-2 days in the endemic area or immediately upon departure.
- Primary Prophylaxis (alternative regimen): 30 mg base orally once daily, starting 1-2 days before travel to an endemic area, taken daily while in the area, and continued for 7 days after leaving.
- Administration: Should be taken with food to minimize gastrointestinal upset.
CRITICAL NOTE: Testing for Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency is mandatory prior to initiation. Dosage adjustments or alternative regimens may be required based on G6PD activity levels.
Precautions
- G6PD Testing is Mandatory: The single most important precaution. Primaquine can cause severe hemolysis in patients with G6PD deficiency. Quantitative G6PD testing must be performed before prescribing, and the result must be known and normal prior to administration.
- Pregnancy: Contraindicated during pregnancy due to the unknown G6PD status of the fetus and risk of fetal hemolysis. Use in pregnancy is only considered if the benefit outweighs the significant risk and the mother is known to have normal G6PD activity.
- Lactation: Should generally be avoided in breastfeeding women unless the infant has been tested and has normal G6PD activity.
- Nicotinamide Adenine Dinucleotide (NADH) Methemoglobin Reductase Deficiency: Can exacerbate the drug’s potential to induce methemoglobinemia.
- Pre-existing Conditions: Use with caution in patients with pre-existing hematological conditions (e.g., anemia, granulocytopenia) or active rheumatoid arthritis or lupus erythematosus, which may be exacerbated.
Contraindications
- Confirmed or suspected Glucose-6-Phosphate Dehydrogenase (G6PD) deficiency. This is an absolute contraindication for the standard 14-day regimen.
- Pregnancy.
- Known hypersensitivity to primaquine or other 8-aminoquinolines.
- Concurrent use of other agents with high potential for causing hemolysis or bone marrow suppression.
Possible side effect
The majority of side effects are mild and dose-related.
- Common: Abdominal cramps, nausea, vomiting, epigastric distress, chest discomfort. These can often be mitigated by taking the drug with food.
- Serious (primarily in G6PD deficient individuals):
- Hemolytic Anemia: The most significant adverse effect, characterized by dark urine, fatigue, tachycardia, pallor, and shortness of breath.
- Methemoglobinemia: Can cause cyanosis (bluish skin), chocolate-brown colored blood, headache, fatigue, and shortness of breath.
- Leukopenia (low white blood cell count) and Granulocytopenia.
- Other: Headache, visual disturbances, pruritus (itching).
Drug interaction
Primaquine has the potential to interact with several other medications:
- Other Hemolytic Drugs: Concurrent use with drugs that can cause hemolysis (e.g., sulfonamides, dapsone, nitrofurantoin) increases the risk of severe hemolytic anemia.
- Bone Marrow Suppressants: Drugs that suppress bone marrow function may compound the myelosuppressive effects of primaquine.
- QT-Prolonging Agents: Primaquine may prolong the QT interval; caution is advised when co-administering with other drugs known to have this effect (e.g., certain antiarrhythmics, antipsychotics, antibiotics).
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. They should simply resume the regular dosing schedule with the next planned dose. Maintaining the 14-day course is critical for efficacy. Patients should be instructed to contact their healthcare provider for guidance if multiple doses are missed.
Overdose
Symptoms of overdose are an exaggeration of its known adverse effects, primarily severe abdominal cramps, vomiting, burning epigastric distress, central nervous and cardiovascular disturbances, cyanosis (from methemoglobinemia), methemoglobinemia, hemolytic anemia, granulocytopenia, and acute renal failure. There is no specific antidote. Management is supportive and symptomatic, including gastric lavage if ingestion was recent, monitoring of vital signs and hematological parameters, and treatment of methemoglobinemia with methylene blue if severe (NOTE: Methylene blue is itself contraindicated in G6PD deficiency). Treatment in a hospital setting is essential.
Storage
- Store at room temperature, between 20°C to 25°C (68°F to 77°F).
- Protect from light and moisture.
- Keep in the original container, tightly closed.
- Keep out of reach of children and pets.
Disclaimer
This information is for educational purposes only and 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 before starting any new treatment. Never disregard professional medical advice or delay in seeking it because of something you have read here. The use of primaquine requires a prescription and must be managed by a qualified healthcare professional who has access to the patient’s full medical history and can perform necessary pre-treatment testing (e.g., G6PD).
Reviews
- WHO Guidelines for Malaria (2023): “Primaquine is recommended for the radical cure of P. vivax and P. ovale malaria… G6PD testing is recommended before primaquine is given for radical cure to avoid haemolytic anaemia. If a patient has G6PD deficiency, primaquine should not be given.”
- CDC - The Yellow Book (Health Information for International Travel): “Primaquine is the only medication approved by the FDA for radical cure and terminal prophylaxis of P. vivax and P. ovale infections… Primaquine may cause hemolytic anemia in people with G6PD deficiency. Before prescribing primaquine, patients must be screened for G6PD deficiency using a quantitative test.”
- Infectious Disease Specialist, Academic Medical Center: “Primaquine remains an irreplaceable tool in our arsenal. While the necessity for G6PD testing adds a step, it is a non-negotiable one. When used correctly, it is the difference between treating an episode and actually curing a patient of vivax malaria for good. It’s a classic drug that is more relevant than ever in the goal of malaria elimination.”