In addition, these activated platelets and microparticles provide a surface onto which coagula- tion factor complexes can assemble to promote thrombin generation. This phenomenon can then trigger venous or arterial thrombosis with venous thrombosis being more common.97 Osteoporosis is caused by binding of heparin to osteoblasts,32 which then release factors that activate osteoclasts in an 1.1.7 Reversing the Anticoagulant Effect of Heparin: One advantage of heparin is that IV protamine sulfate can rapidly reverse its anticoagulant effects. Protamine sulfate is a basic protein derived from sh sperm that binds to heparin to form a stable salt. One milligram of protamine sulfate will neutralize approx- imately 100 units of heparin. Therefore, a patient who bleeds immediately after receiving an IV bolus of 5,000 units of heparin should receive about 50 mg of protamine sulfate. Protamine sulfate is cleared from the circulation with a half-life of about 7 min. Because the half-life of IV heparin is 60 to 90 min when heparin is given as an IV infusion, only heparin given during the preceding several hours needs to be considered when calculating the dose of protamine sulfate that needs to be administered. Therefore, a patient receiving a continuous IV infusion of heparin at 1,250 units/h requires approximately 30 mg of protamine sulfate to neutralize the heparin that was given in the past 2 to 2.5 h. Neutralization of subcu- taneously administered heparin may require a pro- longed infusion of protamine sulfate. The aPTT can be used to assess the effectiveness of protamine sul- fate neutralization of the anticoagulant effects of The risk of severe adverse reactions to protamine sulfate, such as hypotension or bradycardia, can be minimized by administering the protamine slowly. 