Ans. is 'a' Weakest acid found in living organism Heparin is a direct acting anticoagulant Chemical nature and preparationHeparin is a sulfated mucopolysaccharide which occurs in the secretory granules of mast cells.It is the strongest organic acid in the body and in the solution it carries an electronegative charge.It is prepared commercially from a variety of animal tissues (generally porcine intestinal mucosa or bovine lung).Mechanism of Action of HeparinHeparin acts by activating antithrombin which is a naturally occuring inhibitor of activated coagulation factors of intrinsic and common pathway. 'Adverse effects of HeparinBleedingHeparin induced thrombocytopeniaOccurs more commonly in heparin derived from bovine lung.Heparin induced thrombocytopenia should be suspected in whom the platelet count falls by 50% or more after starting heparin and usually occurs 5 or more days after starting therapy.In patients with heparin induced thrombocytopenia following drugs should be substituted.Danaparoid sodiumHirudinArgatrobanOsteoporosis - (most frequently seen in pregnancy)Hypersensitivity reactions & skin necrosis