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Questions And Answer

• Pharmacology and mechanism of action

  Primaquine is active against primary exoerythrocytic stages of all malaria parasites. Primaquine is also effective against latent exoerythrocytic stages of P. vivax and P. ovale responsible for relapse. It possesses gametocytocidal activity against all four species of plasmodia which infect man and could theoretically be used to block malaria transmission. Primaquine has no effect on the erythrocytic stages of plasmodia unless toxic concentrations are achieved^【1】. The mechanism of action of primaquine is unknown. ;

• Indications

  Primaquine is used for the radical treatment of P. vivax and P. ovale infections. It has also been used in large populations to avoid spread of chloroquine-resistant strains of falciparum malaria (through its gametocytocidal action).
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• Side effects

  Primaquine is usually well tolerated in the therapeutic dosage of 15 mg base/day for 14 days, but abdominal pain and gastric distress are common if administered on an empty stomach ^[2] The severity of the gastrointestinal side effects are dose-related, and with larger doses, nausea and vomiting occurs. Rare effects include hypertension and cardiac arrhythmia ^[2]. The principal toxic effect of primaquine is haemolytic anaemia especially in patients with a deficiency of glucose-6-phosphate dehydrogenase (G6PD)^[1]It is estimated that 200–300 million people have G6PD deficiency^[3]. The acute haemolysis is seen after a latent phase of 1–3 days. Drug administration should be discontinued when a darkening of the urine (if possible check urine urobilinogen after 1–3 days) or a sudden decrease in haemoglobin levels occurs. The prognosis of this condition is good and specific treatment usually not needed ^[1]. In addition to haemolytic anaemia, primaquine can also cause methaemoglobinaemia and may rarely suppress bone marrow activity leading to leucopenia ^{[2, 3]}. ;

• Contraindications and precautions

  It is recommended not to use primaquine in patients with conditions affecting bone marrow function or on myelosuppressive medication ^[3].
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• Interactions

  In one study, the effect of primaquine has been studied on the metabolism of antipyrine. Primaquine (45 mg) given 2 hours before antipyrine (300 mg orally), increased antipyrinehalf-life (calculated from 0 to 24 hours) from a mean of 13 to 25 hours and decreased clearance from 3 to 1 l/h ^[4].
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• Preparations

  Available as primaquine phosphate: 26.3 mg phosphate equals 15 mg base.
   
  • Primaquine® (Zeneca) Tablets 13.2 mg.
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• References

  1. Black RH, Canfield CJ, Clyde DF, Peters W, Wernsdorfer WH (1986). Primaquine. In: Chemotherapy of Malaria, 2nd edn, edited by L.Bruce-Chwatt. Geneva: World Health Organization, pp. 61–63.
  2. Primaquine. Martindale: The Extra Pharmacopoeia, 28th edn (1982). (London: Pharmaceutical Press), p. 404.
  3. Primaquine. Therapeutic Drugs, edited by Sir Colin Dollery (1991). (London: Churchill Livingstone), pp. P209–P213.
  4. Back DJ, Purba HS, Park BK, Ward SA, Orme ML’E (1983). Effect of chloroquine and primaquine on antipyrine metabolism. Br J Clin Pharmacol, 16, 497–502. ;

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