Duravet Durafend is a broad-spectrum pellet dewormer that contains 2.27 gm fenbendazole per lb. For the removal and control of large strongyles, small strongyles, pinworms and ascarids. Feeding directions for 1,000 lbs body weight: For strongyles and pinworms - 1 lb in a one day treatment; For ascarids - 2 lbs in a one day treatment. Retreatment may be needed after 6-8 weeks.