Altered heparin pharmacodynamics in patients with pulmonary embolism.

Heparin clearance and pharmacodynamic response were examined in 12 patients being treated for deep venous thrombosis (DVT, 6 patients) or pulmonary embolism (PE, 6 patients). A loading dose of 70 units/kg was administered to DVT patients and 100 units/kg to PE patients followed by an initial infusion rate of 15 or 25 units/kg/h for DVT or PE patients, respectively. Heparin clearance was determined at 4, 12, and 24 h after initiating heparin therapy. The mean heparin clearance in the DVT group was 2,164 ± 1,024 ml/h at 4 h, 2,591 ± 1,239 ml/h at 12 h, and 2,795 ± 1,863 m/h at 24 h. The PE patients had clearances of 1,775 ± 494, 2,004 ± 321, and 2,843 ± 1,000 ml/h at 4, 12, and 24 h, respectively. The difference between the two groups was not statistically significant (p > 0.50). The activated partial thromboplastin time (aPTT) was used as a measure of heparin effect. The maximum effect (EMAX) and concentration required to attain 50% of the maximum effect (EC50) were determined for each group using the Lineweaver-Burke linearization method. The mean EMAX and EC50 for the DVT patients were 130 ± 40.99 s and 1.01 ± 0.70 units/ml, respectively. For the PE patients, the mean EMAX was 418 ± 200 s and the mean EC50 was 4.32 ± 2.81 units/ml. The difference between both groups for each parameter was statistically significant (p