Weight-based heparin protocol using antifactor Xa monitoring.

Purpose: The performance of a weight-based dosing protocol for unfractionated heparin (UFH) infusions using antifactor Xa monitoring was evaluated.

Methods: The first 50 patients to receive a UFH infusion per the new protocol for over 24 hours, regardless of indication, were included in the analysis. All patients received a bolus dose of 26 units/kg, followed by an i.v. infusion of 15 units/kg/ hr based on actual body weight, with no maximum dosage. Antifactor Xa levels were measured every 6 hours after infusion initiation and after every rate change until stable, defined as two consecutive results within the target range of 0.3-0.7 unit/mL, and every 24 hours thereafter. If a level was outside of the target range, the infusion rate was adjusted. Primary outcomes measured included the percentage of patients with a target level at the first test (obtained 6 hours after the start of therapy) and within the first 24 hours. The success of the protocol in obese patients versus nonobese patients was also analyzed.

Results: Of the 50 patients enrolled, 26 (52%) achieved a target antifactor Xa concentration 6 hours after infusion initiation. Only 4 patients did not have an antifactor Xa concentration in the target range within 24 hours. Of the 17 patients weighing more than 100 kg, 16 (94%) had a value within the target range within 24 hours.

Conclusion: A weight-based UFH dosing nomogram using antifactor Xa monitoring resulted in a high percentage of patients achieving target antifactor Xa values within the first 24 hours of therapy.