Experts working with Interpol and the Chinese authorities have struck a major blow against south-east Asia's life-threatening trade in fake malaria tablets.

Hundreds of thousands of counterfeit artesunate pills have been seized and two key drug dealers are now facing trial in China, it has emerged this week. Ominously, however, the investigation also suggests that more than half of artesunate tablets in circulation in the region are bogus. Artesunate is regarded as the drug of last resort against falciparum malaria – the form of the disease responsible for most of the one million malaria-related deaths seen each year.

The emergence over the last ten years of bogus products containing sub-optimal doses of the drug, which can encourage resistance to artesunate, has alarmed tropical disease experts and led to large economic losses for the legitimate manufacturers. The drug is made by companies including Guilin Pharma of the Guangxi autonomous region in southern China, and is particularly important in a part of the tropics afflicted by high levels of malaria that is resistant to older treatments.

The two men facing trial are thought to be responsible for most of the fake pills crossing the China-Myanmar border; their shipments are almost as large as official exports of artesunate to Myanmar and Thailand, according to investigators. But despite many tropical medicine specialists raising the alarm, the problem seems to be getting worse – with up to 52% of tablets the malaria tablets sampled in Vietnam, Cambodia, Laos, Myanmar and on the Thai/Myanmar border counterfeit, according to surveys led by Dr Paul Newton of Oxford University and the Mahosot Hospital in Vientiane, Laos.

Dr Newton said the case could be just the tip of the iceberg in terms of drug counterfeiting, however.
"There are probably other similar problems with other life-saving medicines we are unaware of," he said.

The tablets seized were disguised with authentic-looking packaging, including 16 different types of fake holograms. Most of the counterfeits examined contained no active drug and some had potentially toxic ingredients, including banned pharmaceuticals and even the raw materials for making ecstasy.

However some tablets also contained small amounts of artesunate, possibly to foil screening tests and it is these products, containing sub-optimal doses, that scientists fear will encourage the malaria parasite to become resistant to the drug.

Details of the investigation in the journal PLoS Medicine reveal how tiny amounts of contaminating pollen led investigators to two key sites along the southern Chinese boarder where the pills were stored or manufactured.