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Br J Anaesth. 2011 Dec;107(6):966-71. doi: 10.1093/bja/aer298. Epub 2011 Oct 3.

Determination of residual antiplatelet activity of clopidogrel before neuraxial injections.

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Department of Anesthesiology, Northwestern University Feinberg School of Medicine, 251 E. Huron, Feinberg Pavilion, Suite 5-704, Chicago, IL 60611, USA.



Guidelines recommend discontinuation of clopidogrel for 7 days before a neuraxial injection, while other directives suggest that 5 days might be adequate. We examined the time course of antiplatelet activity after clopidogrel discontinuation in patients undergoing epidural injections.


Thirteen patients were studied at baseline, 3, 5, and 7 days after discontinuation of clopidogrel. P(2)Y(12) determinations were performed using the VerifyNow(®) assay (Accumetrics, San Diego, CA, USA), and clot closure times with stimulation by collagen/epinephrine and collagen/adenosine diphosphate using the PFA-100(®) (Platelet Function Analyzer, Siemens Diagnostics, Deerfield, IL, USA). Repeated-measures ANOVA was used to evaluate P(2)Y(12) platelet reaction units, PFA-100 closure times, and per cent P(2)Y(12) inhibition values. Wilcoxon's signed-rank test was used to compare the frequencies of ≥30%, 11-29%, and ≤10% platelet inhibition between the baseline and subsequent sampling points after discontinuation of clopidogrel.


On day 3 after clopidogrel discontinuation, two subjects had ≥30%, seven subjects had 11-29%, and four subjects had ≤10% platelet inhibition; the corresponding numbers were 0, 3, and 10 subjects on day 5 (P=0.04). There were no differences between the ≥30%, 11-29%, and <10% platelet inhibition groups between days 5 and 7 (0, 0, and 13 subjects, P=1.0). PFA-ADP closure times were normal throughout the study period except in one patient.


These findings support the recommendation that discontinuation of clopidogrel for 5 days allows >70% of platelet function and might be adequate before a neuraxial injection is performed.

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