Zerofen 4% Powder Uses Zerofen 4% is a broad spectrum anthelmintic for the treatment of pigs infected with immature and mature forms of nematodes of the gastro-intestinal and respiratory tracts including: Hyostrongylus rubidus (red stomach worms) Oesophagostomum spp. (nodular worms) Ascaris suum (eel-worm) Trichuris suis (whipworm) Zerofen 4% is also effective in the control of Metastrongylus apri (lungworm) Zerofen 4% Powder has an ovicidal effect on nematode eggs.