The recent Economist has an article on malarial drug resitance.
A large part of the reason for the build-up of resistance is the use of the drug [artemisinin] by itself, as a monotherapy, rather than in combination with another drug. Experts agree that the use of Artemisinin Combination Therapies (ACTs) can greatly delay drug resistance in Africa. ....
The snag is that unscrupulous manufacturers peddle substandard ACTs and monotherapies. Roger Bate, of the American Enterprise Institute and his colleagues, examined the malarial remedies sold by the private sector in six African countries. Their study, recently published in the Public Library of Science (PLoS), found that many were substandard and that a third were artemisinin monotherapies. This, the researchers concluded, “places the future of malaria treatment at risk globally”.