Primaquine

Primaquine is a medication to treat or prevent malaria, a disease caused by parasites. primaquine works by interfering with the growth of parasites in the body. Parasites that cause malaria typically enter the body through the bite of a mosquito. Malaria is common in areas such as Africa, South America, and Southern Asia.

Product dosage: 15 mg
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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 other therapies that target the asexual blood stages of the parasite, primaquine’s primary action is against the dormant hypnozoite forms residing in the liver, preventing relapses and achieving a radical cure. Its gametocytocidal activity also makes it indispensable for reducing malaria transmission in P. falciparum infections. This expert guide details the essential pharmacology, clinical application, and safety profile of this indispensable medication.

Features

• Active Pharmaceutical Ingredient: Primaquine phosphate, USP.
• Pharmacological Class: 8-Aminoquinoline antimalarial.
• Mechanism of Action: Generates reactive oxygen species that are toxic to plasmodia; specifically targets hypnozoites (dormant liver stages) and gametocytes (sexual blood stages).
• Available Formulations: Typically available as 7.5 mg and 15 mg base equivalent tablets.
• Bioavailability: Readily absorbed from the gastrointestinal tract, with peak plasma concentrations occurring within 1-3 hours.
• Metabolism: Rapidly and extensively metabolized primarily by the liver enzyme monoamine oxidase A (MAO-A). The metabolite carboxyprimaquine is the major plasma component, though the specific active metabolites remain under investigation.
• Half-life: Primaquine itself has a short half-life of approximately 3-7 hours, but its active metabolites contribute to a prolonged therapeutic effect.

Benefits

• Achieves Radical Cure: Eradicates the dormant hypnozoites of P. vivax and P. ovale malaria, preventing the characteristic relapses of these infections that can occur months or even years after the initial illness.
• Reduces Malaria Transmission: Its potent activity against gametocytes (the sexual stage of the parasite taken up by mosquitoes) makes it a key tool for cutting the chain of transmission in communities, a critical component of malaria elimination programs.
• Complements Blood-Stage Treatment: Used in conjunction with a fast-acting schizonticide (e.g., chloroquine or artemisinin-based combination therapy) to treat both the acute blood infection and the dormant liver reservoir simultaneously.
• Proven Efficacy: Has been the gold-standard therapy for radical cure for decades, with a well-documented success rate when administered correctly and to appropriate patients.
• Single-Drug Action for Hypnozoites: It is the only widely available medication with reliable activity against hypnozoites, filling a unique and irreplaceable niche in the antimalarial arsenal.

Common use

Primaquine is indicated for:

• Radical cure of Plasmodium vivax malaria: To prevent relapses. It is always administered following initial treatment with a blood schizontocide to clear the acute parasitemia.
• Radical cure of Plasmodium ovale malaria: For the same hypnozoiticidal purpose as in P. vivax.
• Terminal prophylaxis for P. vivax and P. ovale malaria: For individuals with extensive exposure in endemic areas who have likely been infected, to prevent late relapses after they have left the risk area.
• Gametocytocidal action against Plasmodium falciparum: A single, low dose is used in combination with an appropriate artemisinin-based combination therapy (ACT) to eliminate gametocytes and reduce the potential for transmission. This does not treat the acute infection itself.

Dosage and direction

Dosing is based on milligrams of primaquine base. Dosing must be individualized based on the indication, patient factors, and regional parasite sensitivities. All regimens should be taken with food to minimize gastrointestinal upset.

• Radical Cure for P. vivax or P. ovale Malaria:

  • Standard Adult Dose: 30 mg base (52.6 mg primaquine phosphate) orally once daily for 14 days, initiated concurrently with or immediately after the blood schizontocide (e.g., chloroquine).
  • Alternative High-Dose/Short-Course Regimen (in some regions): 45-60 mg base once weekly for 8 weeks may be used in areas with lower relapse strains or for improved adherence, though the 14-day course remains the global standard.
  • Pediatric Dose: 0.5 mg base/kg (max 30 mg base) once daily for 14 days.

• Terminal Prophylaxis:

  • Adult Dose: 30 mg base orally once daily for 14 days after departing the endemic area.
  • Pediatric Dose: 0.5 mg base/kg (max 30 mg base) once daily for 14 days.

• Gametocytocidal for P. falciparum:

  • Single Dose: 45 mg base (0.75 mg base/kg in children) as a single dose, usually given with the first dose of the ACT.

Crucial Direction: Adherence to the full course (especially the 14-day regimen) is absolutely critical for efficacy. Incomplete treatment significantly increases the risk of relapse.

Precautions

• G6PD Testing is Mandatory: The most critical precaution. Primaquine can cause severe hemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency. Quantitative G6PD testing must be performed prior to prescription to ensure a normal level of enzyme activity. Never administer without confirming G6PD status.
• 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 tested and has normal G6PD activity.
• Nicotinamide Adenine Dinucleotide (NADH) Methemoglobin Reductase Deficiency: Patients with this deficiency are at increased risk for drug-induced methemoglobinemia.
• Monitoring: Patients should be advised to monitor for signs of hemolysis (dark urine, jaundice, severe fatigue, shortness of breath) and seek immediate medical attention if they occur.
• Underlying Conditions: Use with caution in patients with pre-existing hematological conditions, rheumatoid arthritis, or systemic lupus erythematosus, which may increase the risk of hematological reactions.

Contraindications

• Known G6PD Deficiency: Absolute contraindication due to the high risk of acute hemolytic anemia.
• Pregnancy: Absolute contraindication.
• Concurrent use with other hemolytic drugs: Contraindicated with other agents known to cause hemolysis or suppress the bone marrow.
• Concurrent use with quinacrine: Quinacrine potentiates the toxicity of primaquine.
• History of a prior severe reaction to primaquine or other 8-aminoquinolines (e.g., tafenoquine).

Possible side effect

• Most Common: Abdominal cramps, nausea, vomiting, epigastric distress. (Taking with food mitigates this).
• Serious:
  • Hemolytic Anemia: The most significant adverse effect, occurring in G6PD-deficient individuals. Presents with dark urine, jaundice, fatigue, tachycardia, and shortness of breath.
  • Methemoglobinemia: Can occur even in patients with normal G6PD, causing cyanosis (bluish skin), chocolate-brown colored blood, headache, fatigue, and dyspnea. Usually resolves upon discontinuation.
  • Leukopenia: Decrease in white blood cell count.
  • Cardiovascular Effects: Rare cases of cardiac arrhythmias.
  • Hypertension.

Drug interaction

• Quinacrine: Markedly increases primaquine plasma levels and toxicity. Contraindicated.
• Other Bone Marrow Suppressants or Hemolytic Agents: (e.g., dapsone, sulfonamides) increase the risk of hematological toxicity.
• Monoamine Oxidase Inhibitors (MAOIs): Theoretical potential for interaction as primaquine is metabolized by MAO-A. Concurrent use should be avoided.

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 normal dosing schedule. Emphasize the importance of completing the full 14-day course to prevent relapse.

Overdose

Symptoms of overdose are an exaggeration of its known adverse effects: severe abdominal cramps, vomiting, burning epigastric distress, central nervous system and cardiovascular disturbances, cyanosis due to methemoglobinemia, hemolytic anemia, granulocytopenia, and acute renal failure. There is no specific antidote. Management is supportive and includes gastric lavage (if recent ingestion), monitoring of hematological parameters and methemoglobin levels, and treatment of symptoms (e.g., methylene blue for severe symptomatic methemoglobinemia, but it is contraindicated in G6PD-deficient patients).

Storage

Store at controlled room temperature (20°C to 25°C or 68°F to 77°F). Keep in the original container, tightly closed, and protected from light and moisture. Keep out of reach of children and pets.

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 a qualified physician or other licensed 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 author assumes no liability for any diagnosis, treatment, decision made, or action taken in reliance upon the information provided.

Reviews

“Primaquine remains the cornerstone of radical cure for vivax malaria. While the 14-day regimen poses adherence challenges, its efficacy is undeniable when used correctly in G6PD-normal patients. The move towards point-of-care quantitative G6PD testing has been a game-changer for its safe deployment in the field.” – Infectious Disease Specialist, Médecins Sans Frontières.

“For malaria elimination programs, the gametocytocidal activity of single-dose primaquine is a powerful, often underutilized, tool. It effectively renders patients non-infectious to mosquitoes, breaking the transmission cycle in communities.” – Public Health Researcher, SE Asia.

“The development of tafenoquine offers a single-dose alternative, but primaquine’s long safety record (with proper screening), low cost, and wide availability ensure it will continue to be a first-line therapy for the radical cure of relapsing malaria for the foreseeable future.” – Clinical Pharmacologist, Academic Medical Center.