The most effective cure for malaria could be lost unless new prescribing guidelines are followed, the World Health Organization (WHO) has warned.
Successive drugs have become ineffective in treating
Drug firms are being urged to stop selling artemisinin on its own to prevent the parasite building up resistance to the drug.
Artemisinin has a 95% malaria cure rate, but only if used in combination with certain other drugs, the WHO says.
If the drug became ineffective, another cure could be 10 years away, it added.
There are at least 300 million cases of the disease each year, resulting in about a million deaths annually.
Although there are several treatments for malaria, widespread resistance to conventional antimalarial drugs has contributed to higher death rates.
Dr Arata Kochi, director of the WHO's malaria department, said there had so far been no treatment failures due to resistance from the parasite which causes the disease.
But his team is watching the situation carefully, and concerns have been raised about decreased sensitivity to the artemisinin combination therapies (ACTs) in South-East Asia.
This is the region that has traditionally been the birthplace of anti-malarial drug resistance.
Dr Kochi said: "Our biggest concern right now is to treat patients with safe and effective medication, and to avoid the emergence of drug resistance.
"If we lose ACTs, we'll no longer have a cure for malaria, and it will be at least 10 years before a new one can be discovered."
In Thailand, a drug called sulfadoxine-pyrimethanime (SP) was initially nearly 100% effective in curing malaria when introduced in 1977.
But within five years it was curing only 10% of cases, because of drug resistance. The once-popular chloroquine has lost its effectiveness in almost every part of the world.
And other malaria medicines such as atovaquone developed resistance within one year of introduction.
WHO malaria expert Dr Pascal Ringwald said it was difficult to say how common the prescription of artemisinins as monotherapies was, but that it was mainly seen in the private sector.
He said monotherapies were no longer used in the treatment of HIV and other major diseases because of concerns about viruses and parasites building up resistance.
The WHO also urged drug companies and the world's research community to rapidly invest in the design of "next generation" antimalarial drugs.
It is hoped that by creating ACTs with numerous drug combinations, that resistance can be overcome.
Professor Sanjeev Krishna, of the centre for infection at St George's University of London, has carried out studies which have suggested artemisinins could theoretically encounter resistance.
He said monotherapies were also less effective than ACTs, and so there was a double benefit to combining artemisinins with other drugs.
He added: "The fact is that this parasite will become resistant to artemisinins like every thing else - it is really a matter of time."
But he also said the fact that so many children still died of malaria while a cure existed had to be addressed.
"The WHO should sit down with drug manufacturers to work out a strategy to ensure that the right drugs get to where they are needed, and at the best price," Professor Krishna added.