title: Determination of residual antiplatelet activity of clopidogrel before neuraxial injections.
abstract: 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. 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.
  
  
  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.
authors.affiliation: Department of Anesthesiology, Northwestern University Feinberg School of Medicine, 251 E. Huron, Feinberg Pavilion, Suite 5-704, Chicago, IL 60611, USA. hbenzon@nmff.org
authors.forename: H T
authors.initials: HT
authors.lastname: Benzon
authors.forename: R J
authors.initials: RJ
authors.lastname: McCarthy
authors.forename: H A
authors.initials: HA
authors.lastname: Benzon
authors.forename: M C
authors.initials: MC
authors.lastname: Kendall
authors.forename: S
authors.initials: S
authors.lastname: Robak
authors.forename: P F
authors.initials: PF
authors.lastname: Lindholm
authors.forename: P G
authors.initials: PG
authors.lastname: Kallas
authors.forename: J A
authors.initials: JA
authors.lastname: Katz
mesh_terms: D000305:Adrenal Cortex Hormones / Q000008:administration & dosage*; D000368:Aged; D000369:Aged, 80 and over; D000077144:Clopidogrel; D005260:Female; D006801:Humans; D007268:Injections, Epidural; D008297:Male; D008875:Middle Aged; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011446:Prospective Studies; D013988:Ticlopidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D013997:Time Factors
chemical_list: D000305:Adrenal Cortex Hormones; D010975:Platelet Aggregation Inhibitors; D000077144:Clopidogrel; D013988:Ticlopidine