the present invention provides a method for preparing a pharmaceutical formulation containing ivermectin and a method and composition that can contain ivermectin plus hexahydropyrazinoisoquinolines and tetrahydropyrimidines . examples of these include praziquantel and pyrantel . a pharmaceutical formulation is provided for use in the treatment of helminthiasis of mammals , and particularly tapeworm , hookworm , roundworm and heartworm of domestic animals and farm animals . the present invention also provides a method of treating helminthiasis in mammals , which method comprises administering to the mammal in need thereof an anthelmintically effective amount of a pharmaceutical formulation of the invention .