Warning that misuse of the most promising new malaria drug could create an incurable strain of the disease, the new chief of the World Health Organization’s malaria program demanded yesterday that 18 pharmaceutical companies stop selling some forms of the drug. After several of the companies refused the demand, the official, Dr. Arata Kochi, made an unusually strong threat for an official of the health organization, saying he would publicly name the companies still selling the drugs three months from now and, if they persisted, would try to disrupt sales of their other medicines. The new drug, artemisinin, a derivative...