Opposition leaders hurled ridicule and defiance at President Thabo Mbeki on Tuesday over his government's continued refusal to expand the use of drugs to prevent mother-to-child transmission of the AIDS virus. Mangosuthu Buthelezi, leader of the mainly Zulu Inkatha Freedom Party (IFP), said he had instructed the IFP premier of KwaZulu-Natal province to dispense with testing and counseling if necessary and offer nevirapine to all pregnant women.