that's why I switched to fenbendazole. according to all I read and advice from vet friend it is safe and very effective on strongyles. I have heard of other people taking it on the net but it was the vet that convinced me it safer than albendazole and much more effective. here is a link he sent me http://www.merckmanuals.com/vet/pharmacology/anthelmintics/benzimidazoles.html