Disclosed is a veterinary anthelmintic composition comprising: a) at least 10 percent w/v of a benzimidazole anthlemintic selected from the group consisting of thiabendazole, cambendazole, parbendazole, mebendazole, fenbendazole, oxfendazole, oxibendazole, albendazole, triclabendazole, salts thereof and combinations thereof and b) a water-immiscible solvent system, which comprises a lactone solvent, an essential oil, and surfactant, wherein the lactone solvent is selected from the group consisting of gamma-hexalactone, delta-hexalactone, delata-nonalactone, delta-nonalactone, delta-decalactone, delta-decalactone, gamma-dodecalactone, gamma-dodecalactone and combinations thereof for the treatment of a parasite in a homeothermic animal.
