Glaxo Smith Kline PLC has announced that it will stop selling one drug used to treat malaria and stop developing another because both appear to lower hemoglobin levels in the blood of some patients, which can lead to anemia.

According to the World Health Organization,the move is a setback to efforts to fight the disease. There are other drugs on the market that treat malaria, but public health officials want as many as possible to promote price competition and to give doctors more options in treating the disease. Malaria is borne by mosquitoes and kills more than one million people each year, mostly in the developing world.