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ANTICOAGULATION

Comparing Direct Thrombin Inhibitors Using aPTT, Ecarin Clotting Times, and Thrombin Inhibitor Management Testing

Coagulation Specialist, Department of Pathology and Laboratory Medicine, University of California, Davis Medical Center, Sacramento, CA

Jeffrey H King, PharmD

Coordinator, Clinical Services Department of Pharmacy, University of California, Davis Medical Center

Kim A Janatpour, MD

Assistant Professor, Department of Pathology and Laboratory Medicine, University of California, Davis Medical Center

William E Dager, PharmD

Anticoagulation Specialist, Department of Pharmacy, University of California, Davis Medical Center

Edward C Larkin, MD

Vice Chair, Department of Pathology and Laboratory Medicine, University of California, Davis Medical Center

John T Owings, MD

Professor, Trauma Division, University of California, Davis Medical Center

Reprints: John T Owings MD, Trauma Division, University of California, Davis Medical Center, 2315 Stockton Blvd., Rm. 4209, Sacramento, CA 95817-2201, fax 916/734-7755, jtowings{at}ucdavis.edu

BACKGROUND: Patients with heparin-induced thrombocytopenia and thrombosis may be acutely anticoagulated with direct thrombin inhibitors (DTIs). The anticoagulation is typically monitored using the activated partial thromboplastin time (aPTT) or ecarin clotting time (ECT).

OBJECTIVE: To compare 14 methods for measuring aPTT, as well as ECT and thrombin inhibitor management test (TIM), in samples containing DTIs.

METHODS: DTIs were added to pooled normal plasma to achieve low (0.1–1.2 µg/mL) and high (1.5–8.0 µg/mL) drug concentrations. Each low-concentration DTI sample was tested using all aPTT reagents, while each low- and high-concentration DTI was tested using the ECT and TIM.

RESULTS: All aPTT reagents had a significant dose-dependent correlation with drug concentration. Only Actin FSL and APTT-S demonstrated equivalent aPTT ratios obtained from any DTI. The TAS-aPTT was the most sensitive aPTT reagent to argatroban, with the aPTT ranging from 52.7 to 121.2 seconds corresponding to 0.1 to 1.2 µg/mL of drug concentration. The TAS-aPTT and Pathromtin were the most sensitive aPTT reagents to bivalirudin, with aPTTs of 87.4 seconds and 101.5 seconds, respectively, at 1.2 µg/mL of drug. Pathromtin was the most sensitive aPTT reagent to lepirudin, with a maximum aPTT of 108.9 seconds at 1.2 µg/mL of drug. There was no statistically significant difference between the TIM and ECT clotting times for each DTI. Lepirudin and bivalirudin ECT and TIM clotting times were equivalent.

CONCLUSIONS: There are unique differences between reagent manufacturers in the monitoring of DTIs. Acceptable alternatives to aPTT monitoring of DTI anticoagulation include the ECT and TIM.

Key Words: activated partial thromboplastin time, anticoagulation, direct thrombin inhibitors

Published Online, July 6, 2004. www.theannals.com, DOI 10.1345/aph.1D565

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