Malaria : Drug as effective in low doses

A new study finds that lower doses of the drug primaquine are as effective at preventing transmission of malaria as standard doses.

Primaquine targets the transmission stages of the malaria parasite, the gametocytes, and is considered an important tool for malaria elimination .

The new study, led by researchers from the London School of Hygiene & Tropical Medicine (LSHTM) in the UK, is published in the latest online issue of The Lancet Infectious Diseases.

The findings are good news because there are not many drugs that target this stage of the disease, and unfortunately, at standard doses primaquine can reduce blood count in people with a red blood cell disorder caused by a deficiency in an enzyme called G6PD.

The inherited blood disorder is common in places where malaria is endemic and so has limited the use of primaquine in those areas.

Because of this side effect, the World Health Organization (WHO) advised that dosage of primaquine be reduced from 0.75 mg/kg to 0.25 mg/kg. However, until now, nobody had formally evaluated the effectiveness of the drug at lower doses. 

Lead author Dr. Alice Chi Eziefula, Wellcome Trust clinical research fellow at LSHTM, says:

"Until now, the use of primaquine was limited because of safety concerns, but lower doses had never been tested formally."

Half of standard dose just as effective

The study took place in Jinja, Uganda, where children without the red blood cell disorder were treated with a malaria drug either on its own or with one of three different doses of primaquine. 

The children were then monitored for 2 weeks to test their malaria gametocytes, and they were kept under observation for another 2 weeks. 

The resuls showed that a dose of 0.4 mg/kg of primaquine, or about half of the previously recommended (standard) dose, was as effective at reducing the transmission potential of individuals with malaria. 

Dr. Chi Eziefula says:

"More questions remain to be answered regarding the best operational strategy for the deployment of primaquine to block malaria transmission."

The next step is to evaluate the effectiveness of the current WHO-recommended 0.25 mg/kg dose of primaquine in people without the red blood cell disorder, and then to test the safety of such a dose in people with the blood disorder. 

Co-author Moses Kamya, a professor with the Infectious Disease Research Collaboration in Kampala, Uganda, says:

"This study provides important contemporary information that allows malaria control programmes in endemic countries in Africa to consider the use of primaquine as part of their efforts to deal with this killer disease."