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Discontinue Plavix Before Assay?

Last week we posted a follow-up question about specimen collection for Plavix efficacy testing. The question was, “How long should patients go without Plavix before aggregometry testing?”

The answers were:

a. 48 hours: 2 (18%)
b. 7 days: 5 (45%)
c. 10 days: 3 (27%)
d. 14 days: 1 (9%)

 Only eleven of us responded, which should be no surprise, since relatively few physicians are ordering platelet aggregometry to monitor Plavix, however our volume is likely to grow. There is good evidence for variation in Plavix dosage effect, possibly inherited, as discussed in Smith SM, Judge HM, Peters G, et al. Common sequence variations in the P2Y12 and CYP3A5 genes do not explain the variability in the inhibitory effects of clopidogrel therapy. Platelets 2006; 17:250-8. The variation is also discussed in the May, 2009 CAP Today in a review article by writer Karen Lusky entitled, “Getting Personal About Antiplatelet Therapy.” This will be an interesting leap forward in antiplatelet resistance testing and molecular diagnosis. Geo.

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