APPROPRIATE USE OF HEPARIN - EMPIRIC VS NOMOGRAM-BASED DOSING

Background: A study involving two groups of patients with cardiovascul ar disease was conducted to compare empiric (clinician-directed) hepar in therapy with therapy based on a nomogram-determined dosage. The com parison was based on (1) the average weight-referenced infusion rate y ielding a therapeutic activated partial thromboplastin lime (APTT) and (2) the time required to reach a therapeutic APTT (55 to 95 seconds) after empiric or nomogram-based heparin therapy was initiated. Methods : Data were collected for patients admitted to the cardiology service at a university health science center in two phases: phase 1 (April 1 through June 30, 1992), involving 95 patients receiving heparin therap y, with 88 patients included in the data analysis, and phase 2 (March 11 through June 11, 1993), involving 156 patients receiving heparin th erapy, with 45 patients receiving nomogram-guided therapy included in the data analysis. Results: In phase 1, 66 patients (75.0%) achieved a therapeutic APTT some time during their heparin therapy, with an aver age time to therapeutic APTT of 20.7+19.1 hours. Regression analysis d emonstrated a statistically significant relationship between the hepar in infusion rate at the time of the patient's first therapeutic APTT a nd the patient's total body weight (r(2)=.3043). An initial infusion r ate based on total body weight (13 U/kg per hour) was therefore used a s the basis for the nomogram in phase 2. In phase 2, 41 patients (91.1 %) achieved a therapeutic APTT at some time during their heparin thera py, with an average time to therapeutic APTT of 13.1+11.9 hours, stati stically significantly shorter than that in phase 1. A greater proport ion of patients in phase 2 compared with patients in phase 1 reached t he therapeutic range within 12 hours (62.2% vs 34.1%) and within 24 ho urs (77.8% vs 54.5%). Conclusions: Use of a weight-based nomogram to d etermine the initial and maintenance heparin infusion rates was associ ated with a higher percentage of patients admitted to the cardiology s ervice reaching the targeted therapeutic APTT range at a time earlier in the course of therapy compared with empiric dosing.