• Identification of subtherapeutic or supratherapeutic levels in patients taking other drugs that are known to affect pharmacokinetics.
• Identification of subtherapeutic or supratherapeutic levels in patients at body weight extremes.
• Patients with deteriorating renal function.
• During perioperative management.
• During reversal of anticoagulation.
• When there is suspicion of overdose.
• Assessment of compliance in patients suffering thrombotic events while on treatment.
Currently, there exists no commercially available reversal agent for any of the NOACs and existing reversal agents for traditional anticoagulants are of limited, if any, use. Drugs under development include agents for the factor Xa inhibitors and for the thrombin inhibitor. Until the time that specific reversal agents exist, supportive care is the mainstay of therapy. In cases of trauma or severe or life-threatening bleeding, administration of concentrated clotting factors (prothrombin complex concentrate) or dialysis (dabigatran only) may be utilized. However, data from large clinical trials is lacking. A recent study of 90 patients receiving an antibody directed against dabigatran has revealed that the anticoagulant effects of dabigatran were reversed safely within minutes of administration; however, drug levels were not consistently suppressed at 24 hours in 20% of the cohort.8
There are no national guidelines nor large scale studies to guide bridging NOACs for procedures. The relatively short half-life for these agents makes it likely that traditional bridging as is practiced for warfarin is not necessary.9 However, this represents a double edged sword; withholding anticoagulation for two doses (such as if a patient becomes ill or a clinician is overly cautious around the time of a procedure) may leave the patient unprotected.
The final question with the new agents is their anti-inflammatory effects. We know that heparin and LMWH have significant pleiotropic effects that are not necessarily related to their anticoagulant effects. These effects are important to decrease the inflammatory nature of the thrombus and its effect on the vein wall. We do not know if the new oral agents have similar effects, as this has never fully been tested. In view of the fact that two of the agents are being used as monotherapy agents without any heparin/LMWH bridge, the anti-inflammatory properties of these new agents should be defined to make sure that such a bridge is not necessary.
Conclusion
So, in summary, although these agents have much to offer, there are many questions that remain to be addressed and answered before they totally replace traditional approaches to anticoagulation, in the realm of VTE. It must not be overlooked that for all the benefits, they each carry a risk of bleeding as they all target portions of the coagulation mechanism. We believe, that as with any “gift horse,” physicians should perhaps examine the data more closely and proceed with caution.
Dr. Wakefield is director of the Samuel and Jean Frankel Cardiovascular Center, Dr. Obi is a vascular surgery fellow, and Dr. Coleman is program director, section of vascular surgery, at the University of Michigan, Ann Arbor. They reported no conflicts of interest.
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