Tests on Key Malaria Drug Start in Cambodia

Testing has started on a malaria drug long shunned in Cam­bo­dia but without which the World Health Organization (WHO) says it will have trouble meeting the government’s goal of eliminating the mosquito-borne parasite for good.

Government health workers started administering small doses of the drug primaquine two weeks ago in the western prov­ince of Pai­lin as part of the WHO-funded, $150,000 trial, said Steven Bjorge, the WHO’s malaria team leader in Cambodia.

“If we can’t use this drug, it will be very hard to eliminate malaria in Cambodia,” Mr. Bjorge said.

With most Cambodians currently at risk of the deadly disease, the government has set it­self the goal of zero malaria deaths by 2020 and no infections by 2025.

This latest drug trial takes aim at one of the two main species of ma­lar­ia in the country—Plasmo­dium vivax, which is responsible for just over a third of all infections.

Unlike the more common spe­cies, Plasmodium vivax is still sus­ceptible to the best available drugs tasked with killing the ma­laria parasite in the blood. What complicates vivax is that it can lay dormant in a person’s liver for months, reinfecting them over and over again after just one mosquito bite.

“You give people DHAP and they’re cured for a while,” Mr. Bjorge said, referring to the drug currently used to fight vivax in the blood, “but then they get sick again.”

Enter primaquine. The drug’s knack for fighting malaria in the liver is well known and has been in use since the 1950s. But here is where things get complicated again. In people short of a particular gene, giving them primaquine causes their red blood cells to break down, impairing the body’s essential work to carry oxygen from the lungs to the rest of the body.

Mr. Bjorge said that condition af­fects up to 10 percent of all Cam­­­­bodians, some less severely than others. So the WHO, working with the government’s Na­tion­al Malaria Center, is looking for the right dose to fight the ma­laria without triggering any se­vere side effects.

To find that balance, Mr. Bjorge said, government health workers in Pailin are giving ma­laria pa­tients—both those with the troublesome genetic condition and those without—a weekly dose for eight weeks and monitoring the results carefully. It will take up to eight months to test all the pa­tients needed for the re­search, he said.

Primaquine is not entirely new to Cambodia.

Mr. Bjorge said the drug was deployed here about 20 or 25 years ago but was soon discontinued following reports of ill effects. Though few details remain on how the drug was administered, the experience has made it anathema among local doctors while some neighboring countries have forged ahead with its use.

By finding the right dose of primaquine, the new trial aims to change that.

Even without primaquine, Cam­bodia has made major gains in bringing malaria deaths and infections down in recent years.

Recorded deaths have fallen from 608 in 2000 to just 40 last year. Thanks to an intense, WHO-led effort to contain the disease in the Greater Mekong Re­gion, re­corded infections have also plummeted by more than 27 percent in the past year alone to 51,752 cases.

The WHO is continuing to boost that effort and is moving its regional malaria office from Bang­kok to Phnom Penh in the process.