From the Guidelines
Pradaxa (dabigatran) primarily affects the activated partial thromboplastin time (aPTT) but has minimal effect on prothrombin time (PT). When a patient is taking Pradaxa, their aPTT will typically be prolonged, though the relationship is not linear at higher concentrations, making it unsuitable for precise dosing adjustments. The effect on aPTT is most pronounced within 2-3 hours after taking the medication when blood levels peak. PT/INR remains relatively unchanged with Pradaxa, which distinguishes it from warfarin therapy. This difference occurs because Pradaxa is a direct thrombin inhibitor that specifically targets thrombin (factor IIa) in the coagulation cascade, rather than affecting multiple clotting factors like vitamin K antagonists.
According to the most recent and highest quality study 1, the sensitivity of standard coagulation tests to dabigatran is as follows:
- PT: little sensitivity
- aPTT: sensitive to DOA
- TT: highly sensitive
- Anti-Xa: little sensitivity
For clinicians monitoring patients on Pradaxa, it's essential to know that standard coagulation tests have limitations in accurately reflecting the anticoagulant effect of the drug, and specialized tests like diluted thrombin time or ecarin clotting time provide better measurement of its activity, though these are not routinely available in many clinical settings 1.
Key points to consider:
- Pradaxa affects aPTT but not PT
- The relationship between Pradaxa and aPTT is not linear at higher concentrations
- Specialized tests are needed for accurate measurement of Pradaxa's anticoagulant effect
- Clinicians should be aware of the limitations of standard coagulation tests when monitoring patients on Pradaxa 1.
From the FDA Drug Label
At recommended therapeutic doses, dabigatran etexilate prolongs the coagulation markers such as aPTT, ECT, TT, and dTT. The aPTT test provides an approximation of dabigatran etexilate capsules anticoagulant effect
Yes, Pradaxa (dabigatran) affects both aPTT and PT/INR is not reliable.
- aPTT is prolonged by dabigatran etexilate.
- There is no information about the effect of dabigatran on PT in the provided text, but it is mentioned that INR is relatively insensitive to the exposure to dabigatran. 2
From the Research
Effect of Pradaxa on Coagulation Tests
- Pradaxa (dabigatran) affects the activated partial thromboplastin time (aPTT) and thrombin time (TT) as determined by the Hemoclot thrombin inhibitor assay in patient plasma samples 3.
- The aPTT demonstrated a modest correlation with the dabigatran level, but the correlation became less reliable at higher dabigatran levels 3.
- Different aPTT reagents differed in their responsiveness to dabigatran, suggesting individual laboratories must determine their own therapeutic range for their aPTT reagent 3.
Influence of Dabigatran on Coagulation Factors and Inhibitors
- Dabigatran affects the activities of many coagulation factors, including factors II, V, VIII, and IX, as well as the antifactor VIII inhibitor 4.
- The prothrombin time (PT) and aPTT are often normal in spite of therapeutic dabigatran plasma levels 5.
- The thrombin clotting time (TCT) correlated well and linearly with dabigatran levels below the 50th percentile, but was unmeasurable above it 5.
Relation between Dabigatran Concentration and Coagulation Tests
- The dabigatran concentration was strongly and positively correlated with activated clotting time (ACT) and aPTT (r = 0.87, p <0.001; and r = 0.76, p <0.001; respectively) 6.
- The dilute thrombin time (dTT) correlated best with plasma dabigatran concentrations (r(2) = 0.95) 7.
- Plasma fibrinogen concentrations explained some of the residual variability in TT values after taking plasma dabigatran concentrations into account (r(2) = 0.12, P = 0.02) 7.