Invincible no more.
Drugs derived from sweet wormwood show signs of resistance.

Credit: USDA

Vulnerability Seen in Powerful Malaria Drug

By Gretchen Vogel
ScienceNOW Daily News
5 December 2005

Based on extracts from the sweet wormwood plant Artemisia annua, used for centuries in Chinese traditional medicine, artemisinin and its derivatives such as artesunate and artemether had seemed almost miraculous in their effectiveness. Even in areas where multidrug-resistant parasites render most therapies useless, treatments containing artemisinins cure up to 90% of patients within days. Because the compounds are powerful and fast-acting, scientists hoped that they might pack such a wallop that resistant strains wouldn't get a foothold. To be doubly safe, officials have stressed the importance of using the compounds only in tandem with other drugs in an approach called artemisinin combination therapy (ACT).

The importance of that warning is highlighted in the 3 December Lancet, where immunologist Ronan Jambou and his colleagues at the Institut Pasteur in Dakar, Senegal, compared the effects of different drugs on malaria parasites in three different parts of the world. In an effort to develop an early-warning system for signs of resistance, the researchers took blood samples from 530 malaria patients in Cambodia, French Guyana, and Senegal. In Cambodia, where use of the drug has been tightly regulated as part of ACT therapy, the researchers found no evidence of resistance. But in Senegal and in French Guyana, where artemisinins are either unregulated or approved for use without other drugs, they found signs that parasites could evade the drug, along with evidence for several mutations that are likely to confer resistance. "This is the first step toward treatment failure with this drug," Jambou says.

The observation is not a complete surprise, says Pascal Ringwald of the World Health Organization. "When you use drugs in monotherapy, sooner or later you will develop drug resistance," he says. But he notes the news comes several years sooner than most people expected. Even so, Jambou says, if countries heed the early warning and crack down on unrestricted use of the drug, there is a good chance they can preserve artemisinin's usefulness. "If we use these compounds carefully," he says, "we still have time."

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