Continued from Page 1
The clot does not stop here
“Even with the discontinuation of heparin, the process of thrombosis formation continues,” says Miller. The return of the platelet count to normal or baseline may be delayed for weeks in some patients. Without immediate alternative anticoagulation therapy, there remains a high risk of developing thromboembolic disease in the period following cessation of heparin.
Drugs used as alternatives to heparin include lepirudin (Refludan) and Argatroban (see table, next page). Both drugs are direct thrombin inhibitors and reduce the risk of serious complications of HIT type II.
Warfarin (Coumadin) is contraindicated for initial treatment in these patients due to its association with further complications, including tissue ischemia, necrosis, and gangrene. However, once platelet levels return to normal and treatment is started with a direct thrombin inhibitor, warfarin may be an option for long-term anticoagulation.
“For nurses, it’s counterintuitive and unnerving to treat low platelet counts with anticoagulants,” says Miller, “but with HIT, you have to change your mindset.”
With the paradoxical nature of HIT type II, nurses must embrace that change in mindset and monitor heparin-exposed patients for both bleeding and clotting complications. Do not let a clot slip through the cracks because HIT and its potentially lethal consequences are the last things you might expect.
Direct thrombin inhibitors used in the
management
of HIT type II |
REFLUDAN (lepirudin)* |
|
Dosing
- IV bolus – 0.4 mg/kg (Refludan is dosed by weight up to 110 kg dose. Patients equal to or greater than 110 kg receive the 110 kg dose). Administer over 15 to 20 seconds, followed immediately by continuous IV infusion.
- Continuous IV infusion – 0.15 mg/kg/hour as long as clinically indicated, generally two to 10 days
Monitoring therapy
- Determine a baseline aPTT ratio before starting Refludan. Do not start if ratio is equal to or greater than 2.5.
- Target range for aPTT ratio is 1.5 to 2.5 throughout therapy.
- If baseline aPTT ratio is less than 2.5, administer Refludan bolus and start infusion.
- Determine aPTT ratio 4 hours after starting Refludan infusion and at least daily thereafter.
- For patients with serious liver injury or an increased risk of bleeding, more frequent aPTT monitoring is highly recommended. Monitoring the aPTT and creatinine clearance more frequently may prevent a relative overdose in patients at risk of renal impairment during the course of Refludan therapy.
Adjusting therapy
- If aPTT ratio is out of target range, confirm at once unless clinical need requires immediate reaction.
- For confirmed aPTT ratio greater than 2.5, stop infusion for 2 hours, restart at 50% reduction in infusion rate, and redetermine aPTT ratio 4 hours after restart.
- If confirmed aPTT ratio is less than 1.5, increase infusion rate in steps of 20% and redetermine aPTT ratio 4 hours after each dosage change.
- In general, an infusion rate of 0.21 mg/kg/hour should not be exceeded without checking for coagulation abnormalities.
|
|
| ARGATROBAN* |
|
Dosing
- Continuous IV infusion – 2 micrograms per kilogram per minute (there is no IV bolus).
Monitoring therapy
- Determine a baseline aPTT before starting Argatroban.
- Target range for aPTT is 1.5 to 3 times baseline, not to exceed 100 seconds.
- Determine aPTT 2 hours after initiation of therapy.
Adjusting therapy
- Titrate dose as clinically indicated until the steady-state aPTT is 1.5 to 3 times the baseline value, not to exceed 100 seconds.
- Doses greater than 10 micrograms per kilogram per minute should not be administered.
|
Sources
Information compiled from www.argatroban.com, www.refludan.com, and www.findarticles.com/.
Caution: Review current drug information before administering and monitoring medications. |
*Normal ranges for platelet counts may vary between individual laboratories.
Catherine Spader, RN, is a freelance writer.
References
1. Heparin-induced thrombocytopenia. Berlex Laboratories/Refludan wesite. Available at: www.refludan.com/hit/index.htm. Accessed January 17, 2005.
2. Rationale for the development of Argatroban. Glaxosmithkline/Argatroban website. Available at: www.argatroban.com/clinic_08.htm. Accessed January 18, 2005.
3. Heparin-Induced Thrombocytopenia. Clinicians Publishing Group and Gale Group on Findarticles website. Available at: www.findarticles.com/p/ articles/mi_m0BUY/
is_2_11/ai_71710879. Accessed January 13, 2005.
Bibliography
Brandt, J. Diagnosing heparin-induced thrombocytopenia. College of American Pathologists website. Available at www.cap.org/apps/ docs/cap_today/case_study/coag6.html. Asscessed January 11, 2005.
The FDA Medical Products Reporting Program. FDA website. Available at www.fda.gov/medwatch/safety/1998/jun98.htm. Accessed January 18, 2005.
Heparin-induced thrombocytopenia.Warfarin Institute of America website. Available at: http://warfarinfo.com/hit.htm. Accessed January 4, 2005.
Updated prescribing information for Lovenox. FDA
website. Available at http://www.fda.gov/medwatch/SAFETY/2004/Lovenox_HCP.pdf. Accessed January
18, 2005.
|
Reply to Article