About Protamine Sulphate A highly cationic peptide, Heparin antagonist, Heparin antidote,Antihaemorrhagic. Mechanism of Action of Protamine Sulphate It is a basic protein obtained from sperm of a fish and acts as a heparin antagonist. It neutralizes heparin in a weight for weight basis (1mg is needed for every 100U of heparin. In the presence of heparin the drug forms a salt that neutralizes the anticoagulant effects of both drugs. Indications for Protamine Sulphate Antidote for heparin