Heparin dosage adjustment in patients with deep-vein thrombosis using heparin concentrations rather than activated partial thromboplastin time.

In patients with deep-vein thrombosis, heparin dosage adjustment based on measurement of heparin concentrations in whole blood was compared with conventional dosage adjustment based solely on activated partial thromboplastin time (APTT) measurement. Initially, all patients were given i.v. bolus doses of heparin sodium 70 units/kg followed by continuous infusion of 16 units/kg/hr. Seventeen patients (group 1) had their initial heparin dosages adjusted according to the results of the APTT value four hours after the start of heparin therapy; subsequent adjustments were made to maintain APTT values within the therapeutic range of 1.5 to 2.5 times the patient's baseline control. Fifteen patients (group 2) had heparin dosage adjusted four hours after the start of heparin infusion, based on apparent heparin clearance using the two-point method of Chiou et al., to maintain whole-blood heparin concentrations of 0.3 to 0.6 units/mL. APTT values less than 1.5 times control occurred in about 12% of group 1 patients at 8, 12, and 24 hours and in 11 of 17 (65%) for at least one value during the study. In group 2 patients, no APTT values were less than 1.5 times control. The patients in group 2 had faster symptomatic improvement and shorter hospital stays. Heparin dosing based on measurement of whole-blood heparin concentrations and application of a practical two-point pharmacokinetic model was superior to dosing based on APTT values.