Appropriate use of heparin. Empiric vs nomogram-based dosing.
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.
Gunnarsson
P S
PS
School of Pharmacy, University of North Carolina at Chapel Hill.
Sawyer
W T
WT
Montague
D
D
Williams
M L
ML
Dupuis
R E
RE
Caiola
S M
SM
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D004334:Drug Administration Schedule; D005260:Female; D006493:Heparin / Q000008:administration & dosage*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D010314:Partial Thromboplastin Time
D006493:Heparin