Dave McGlasson forwarded Samama MM, Contant G, Spiro TE, Perzborn E, Le Flem L, Guinet C, Gourmelin Y, Rohde G, Martinoli JL. Laboratory assessment of rivaroxaban: a review. Thromb J. 2013;11:11–18, linked below. The article supports measuring rivaroxaban with the chromogenic anti-Xa assay using rivaroxaban calibrators and controls, and concedes that the prothrombin time (PT) in seconds may be used provided the thromboplastin reagent is sensitive to rivaroxaban. The authors caution that PT reagents vary widely in rivaroxaban sensitivity and that the PT is affected by coagulopathies and inhibitors. Though the chromogenic anti-Xa method accurately measures plasma rivaroxaban concentration, it does not directly assess its degree of anticoagulation in the sense that the PT reflects the anticoagulant effect of Coumadin, or the partial thromboplastin time (PTT) reflects heparin efficacy.
It is impossible to conceive of a randomized double-blind placebo-controlled clinical trial that relates rivaroxaban concentration, and by extension, the concentration of any of the new oral anticoagulants (NOACs) to thrombosis risk when underdosed or bleeding risk in an overdose. Plasma concentration data from clinical trials do not automatically reflect the patient’s clinical response. It seems that our best approach may be to painstakingly collect national or world-wide case-based information into a single database so that therapeutic ranges may be developed on an outcomes basis. To add complexity, the data must be expressed by time interval of specimen collection after drug administration, as NOAC plasma concentrations, unlike Coumadin, vary widely from peak to trough. This approach could be simultaneously applied to unfractionated and low molecular weight heparin and synthetic pentasaccharides, as therapeutic target ranges for these mainstays should also be confirmed by outcomes studies.
To see the complete Samama review, click here: 1477-9560-11-11