primaquine

primaquine is an essential medication in the global fight against malaria, specifically used to prevent relapses of the disease caused by Plasmodium vivax and Plasmodium ovale. It belongs to the 8-aminoquinoline class of drugs and acts against the dormant liver stages, or hypnozoites, of these parasites, a property not shared by most other antimalarials. Developed during the World War II-era research programs, its use is carefully managed due to the risk of severe hemolytic anemia in individuals with glucose-6-phosphate dehydrogenase deficiency.

Medical uses

The primary medical use is the radical cure of Plasmodium vivax and Plasmodium ovale malaria, eliminating both the acute blood-stage infection and the dormant liver forms to prevent relapse. It is also employed as terminal prophylaxis for travelers leaving endemic areas and has a role in preventing the transmission of Plasmodium falciparum gametocytes, contributing to malaria control efforts. Guidelines from the World Health Organization and the Centers for Disease Control and Prevention recommend its use in specific regimens, often following initial treatment with drugs like chloroquine or artemisinin-based combination therapies. Its use requires prior screening for glucose-6-phosphate dehydrogenase deficiency to mitigate the risk of adverse hematological events.

Adverse effects

The most significant adverse effect is dose-dependent hemolytic anemia in patients with glucose-6-phosphate dehydrogenase deficiency, an inherited condition prevalent in many malaria-endemic regions. Other common gastrointestinal effects include nausea, abdominal pain, and vomiting. At higher doses, it can cause leukopenia and methemoglobinemia, which may present as cyanosis. Contraindications include pregnancy, significant rheumatoid arthritis, and systemic lupus erythematosus, due to the potential for exacerbating these conditions.

Pharmacology

Primaquine is metabolized primarily in the liver by the cytochrome P450 enzyme system, particularly CYP2D6, into active metabolites believed to be responsible for its anti-hypnozoite activity. Its mechanism of action involves generating reactive oxygen species that interfere with the parasite's mitochondrial function and other essential processes. The drug exhibits poor activity against the asexual blood stages of malaria parasites but is highly effective against the latent liver stages and sexual gametocytes. Pharmacokinetics show rapid absorption and a short half-life, necessitating a prolonged treatment course over 14 days for radical cure.

History

The discovery stemmed from the extensive antimalarial research programs coordinated by the United States Army and the Office of Scientific Research and Development during World War II, which screened thousands of compounds. It was identified from a series of 8-aminoquinolines investigated at the University of Chicago and other institutions, succeeding the related but more toxic drug pamaquine. Widespread clinical use began after the war, becoming a cornerstone for managing relapsing malaria. Its role was further solidified through large-scale studies by organizations like the World Health Organization in regions such as Southeast Asia and the Western Pacific.

Society and culture

Primaquine is on the World Health Organization's List of Essential Medicines and is a critical tool for malaria elimination campaigns, particularly in the Asia-Pacific region. Access and use are influenced by the cost and availability of glucose-6-phosphate dehydrogenase deficiency testing. The drug has been the subject of numerous clinical trials, including those conducted by the Armed Forces Research Institute of Medical Sciences and the Mahidol University in Thailand. Generic versions are manufactured by several pharmaceutical companies, and its use is a key component of public health strategies endorsed by the Roll Back Malaria Partnership.

Category:World Health Organization essential medicines Category:Antimalarial agents