Protamine sulfate is a drug that reverses the anticoagulant effects of heparin by binding to it.
Protamine was originally isolated from the sperm of salmon and other species of fish but is now produced primarily through recombinant biotechnology. It is a highly cationic peptide. It binds to heparin to form a stable ion pair which does not have anticoagulant activity; on its own, protamine has a weak anticoagulant effect. The complex of heparin and protamine is then removed and broken down by the reticuloendothelial system.