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Article
March 13, 1995

Appropriate Use of Heparin: Empiric vs Nomogram-Based Dosing

Author Affiliations

From the Schools of Pharmacy (Messrs Gunnarsson, Sawyer, and Caiola, Dr Dupuis, and Ms Montague) and Medicine (Dr Williams), University of North Carolina at Chapel Hill, and the Department of Pharmacy, University of North Carolina Hospitals, Chapel Hill (Messrs Gunnarsson and Sawyer, Dr Dupuis, and Ms Montague).

Arch Intern Med. 1995;155(5):526-532. doi:10.1001/archinte.1995.00430050104011
Abstract

Background:  A study involving two groups of patients with cardiovascular disease was conducted to compare empiric (clinician-directed) heparin therapy with therapy based on a nomogram-determined dosage. The comparison was based on (1) the average weight-referenced infusion rate yielding a therapeutic activated partial thromboplastin time (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 therapy, with 88 patients included in the data analysis, and phase 2 (March 11 through June 11, 1993), involving 156 patients receiving heparin therapy, 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 average time to therapeutic APTT of 20.7+19.1 hours. Regression analysis demonstrated a statistically significant relationship between the heparin infusion rate at the time of the patient's first therapeutic APTT and the patient's total body weight (r2=.3043). An initial infusion rate based on total body weight (13 U/kg per hour) was therefore used as 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 therapy, with an average time to therapeutic APTT of 13.1+11.9 hours, statistically significantly shorter than that in phase 1. A greater proportion of patients in phase 2 compared with patients in phase 1 reached the therapeutic range within 12 hours (62.2% vs 34.1%) and within 24 hours (77.8% vs 54.5%).

Conclusions:  Use of a weight-based nomogram to determine the initial and maintenance heparin infusion rates was associated with a higher percentage of patients admitted to the cardiology service reaching the targeted therapeutic APTT range at a time earlier in the course of therapy compared with empiric dosing.(Arch Intern Med. 1995;155:526-532)

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