Pre-emptive warfarin dose adjustment can adversely affect INR
MedWire News: Pre-emptive warfarin dose-reduction among patients initiating prednisone therapy increases the likelihood of a subtherapeutic international normalized ratio (INR) compared with reactive warfarin dose adjustment, US researchers report.
The pre-emptive strategy also reduced the proportion of patients with a supratherapeutic INR, but the effect was not statistically significant, say Kellie Vavra (Kaiser Permanente, Denver, Colorado) and colleagues.
"Regardless of the strategy chosen, prompt monitoring of the INR after initiation of prednisone appears to be a worthwhile practice," remark the researchers in the Journal of Thrombosis and Thrombolysis.
They explain that co-administration of the anti-inflammatory drug prednisone with warfarin increases the risk for over-anticoagulation, as reflected by an elevated INR.
To evaluate the utility of pre-emptive warfarin dosage adjustment for preventing non-therapeutic INR following prednisone-warfarin co-administration, Vavra and team carried out a randomized controlled trial.
Warfarin-receiving patients who had been prescribed oral prednisone were randomly assigned to receive either a pre-emptive warfarin dose-reduction of between 10% and 20% (intervention group, n=20) or reactive warfarin dose-adjustment (control group, n=17) in response to an out of range INR.
The researchers report that the median INR change was 1.0 and -0.4 for the control and intervention groups, respectively.
More control patients experienced an INR ≥ 1 point over the upper limit of the patient-specific INR target range compared with the intervention group, at 5 (29.4%) versus 2 (10%), but the difference was not statistically significant.
In contrast, a higher proportion of intervention patients had a subtherapeutic follow-up INR compared with controls, at 40% versus 5.9%.
One patient from each group experienced warfarin-associated bleeding and no thromboembolic complications were observed. The researchers note however, that the small study size meant that their ability to determine the effect of either management strategy on bleeding or thromboembolism risk was limited.
They conclude that patient data, such as the most recent INR value, may be helpful in determining which management strategy to utilize. Those with high INR values may benefit from pre-emptive dose-reduction, whereas this strategy should probably be avoided in patients with an INR already at the lower end of the therapeutic range, says the team.
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By Laura Dean