Heparin – binds to AT III – inactivation of factors IIa, IXa, Xa, XIa, XIIa. – used as anticoagulant. Large molecular weight substance.
On long term adminstration it will bind to a factor ie. Platelet factor 4 present on the membrane of platlets. There by making the platelets antigenic. So destruction by immune reaction. Decreased platelets in circulation.