High-dose Intravenous Dalteparin Can be Monitored Effectively Using Standard Coagulation Times

The objective of this study was to examine the pharmacokinetics of intravenous dalteparin (Fragmin, Pharmacia-Upjohn, Peapack, NJ) and to assess the accuracy of standard coagulation-based monitoring techniques as an estimate of drug concentration with which to guide dosing. Knowledge of the kinetic behavior of low-molecular-weight heparins (LMWHs) and the possible utility of coagulation times for monitoring may aid in the development of safe and effective dosing algorithms for percutaneous coronary interventions. Twenty normal volunteers were treated at 2-week intervals with each of three intravenous dalteparin doses. Measurement of anti-IIa, anti-Xa, activated partial thromboplastin time (aPTT), activated clotting time (ACT), and low-range ACT was performed at baseline and at seven additional time points over 8 hours. The half-life of intravenous dalteparin is 77 minutes with slight dose-related variation. The aPTT, LR-ACT, and standard ACT are prolonged after dalteparin administration with the increase closely correlated to anti-Xa activity (aPTT, r = 0.85; LR-ACT, r = 0.79). Classification of anticoagulation intensity range using aPTT or LR-ACT in comparison to anti-Xa activity (0.5-0.99, 1.0-1.49, 1.5-2, >2) displays a level of agreement (kappa: aPTT = 0.69, LR-ACT = 0.59) that is comparable to values reported for coagulation time guidance of unfractionated heparin administration. Standard coagulation times are sensitive to the anticoagulant effect of dalteparin with a degree of correlation that suggests their utility for estimating drug concentration during high dose therapy. Trials establishing a relationship between monitoring and clinical efficacy, and the risk/reward of different treatment ranges alone or in combination with GPIIb/IIIa inhibitors and clopidogrel, are necessary.