Hi George, We have a question about performing mixing studies following fondaparinux or enoxaparin administration. How long do you recommend waiting (# half lifes) to perform mixing studies after these medications are administered? Thanks, Carla Purvis,Parkview Regional Medical Center, Fort Wayne, IN.
Hi, Carla, and thank you for the question. Enoxaparin has a 4-hour half-life and full coagulation activation is restored soon after it is discontinued, so I would suggest waiting approximately 16 hours, or four half-lives, provided the glomerular filtration rate is > 50 mL/minute. Fondaparinux has a 12–17 half-life, so I suggest waiting a minimum of 48 hours, assuming full kidney function.
Although you cannot use the partial thromboplastin time (PTT) to monitor enoxaparin (Lovenox) therapy, enoxaparin does slightly prolong the PTT, so you must wait until you can confirm the PTT is unaffected by the drug. Fondaparinux is a little different. Since fondaparinux suppresses only factor Xa, it has no effect on the PTT, thus you may be able to do PTT mixing studies sooner than 48 hours. If you are planning to perform PT mixing studies, neither drug prolongs the PT, so you can proceed at your convenience.
Thanks again for your question, and let’s watch for any comments describing local laboratory policies.