Determination of residual antiplatelet activity of clopidogrel before neuraxial injections

Background. 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. Methods. Thirteen patients were studied at baseline, 3, 5, and 7 days after discontinuation of clopidogrel. P₂Y₁₂ 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 P₂Y₁₂ platelet reaction units, PFA-100 closure times, and per cent P₂Y₁₂ inhibition values. Wilcoxons 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. Results. 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. Conclusions. 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.