Assessment of weight-based versus standard dosing of heparin in patients with unstable angina.

OBJECTIVE

To assess whether a weight-based dosing regimen (80 u/kg + 18 u/kg/h) or a standard-fixed dose regimen (5000 u + 1000 u/h) of heparin is more appropriate in patients with unstable angina (UA).

METHOD: A drug use evaluation was conducted. Patient data for all patients weighing less than 100 kg who were in the coronary care unit of a Veterans Administration Hospital and who received heparin for UA (>24 h) over a 7-month period were included. For the first 4 months, patients were given standard heparin dosing and in the final 3 months patients were given heparin based on weight. The proportion of patients achieving activated partial thromboplastin times (aPTTs) that were at least therapeutic during therapy, the time to achieve the aPTT at a level that was at least therapeutic, and the number of patients with aPTTs over the therapeutic range were compared between groups.

RESULTS

Patients in the group receiving weight-based heparin therapy (n = 23) were significantly more likely to achieve an aPTT that was at least therapeutic than patients receiving standard therapy (n = 42, 100% vs. 76%, respectively, P = 0.011). When all the patients in each group who achieved an aPTT that was at least therapeutic were compared, the weight-based group achieved the levels significantly faster than the standard-fixed dosing group (7.3 +/- 6.1 vs. 22.6 +/- 17.6 h, respectively, P = 0.0003). However, the use of weight-based dosing was associated with a higher incidence of achieving supertherapeutic aPTTs than standard therapy (78.3% vs. 50.0%, respectively, P = 0.049).

CONCLUSION

Patients with UA may achieve therapeutic aPTTs faster than those on standard therapy but they also have a higher risk of achieving a supertherapeutic aPTT.