Clopidogrel Platelet Function Tests

Caveats — Other Reasons for Poor Response to Clopidogrel

December 2011

There are several other factors which are known to affect clopidogrel metabolism. Smoking, caffeine and use of the herb St. John’s wort will affect clopidogrel metabolism. Medications that are metabolized by CYP enzymes other than the CYP2C19 enzyme can cause variability in clopidogrel metabolism. Some medications are known to increase the activity of the CYP2C19 enzyme, while other will decrease the activity of the enzyme. Both diabetes and high body mass index are independent risk factors for poor metabolism of clopidogrel regardless of CYP2C19 status. There is another enzyme which may affect clopidogrel variability more than the CYP2C19 enzyme and this is the paroxonase-1 (PON1) enzyme.

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Other Reasons for Poor Response to Clopidogrel

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Jump to section:

• Introduction
• Learning Objectives
• Platelet Function Tests for the Detection of Clopidogrel Resistance¹
• Platelet Function Tests for the Detection of Clopidogrel Resistance
• Caveat: There Is No Perfect Platelet Function Test...
• Problems With Testing For Clopidogrel
• How We Choose a Testing Method
• Methodology Table
• Platelet Function Testing Available at Mayo Clinic Florida
• Light Transmission Platelet Aggregometry Studies (LTA)
• Platelet Aggregation (Cont'd)
• Normal Patient
• Accumetrics VerifyNow Test
• VerifyNow P2Y₁₂ Test
• P2Y₁₂ Test Interferences
• P2Y₁₂ Antagonists²
• Can These Platelet Function Tests Be Used for Ticagrelor (Brilinta/Brilique)?
• PFA-100
• PFA–100 (Cont'd)
• INNOVANCE PFA P2Y
• TEG — Platelet Mapping
• Results of VerifyNow Testing
• 2009–2011 Clopidogrel Response at 30%
• Genetic Testing: Clopidogrel Metabolism
• Clopidogrel Metabolism
• Number of Gene Polymorphisms
• Clopidogrel Metabolism and Genetic Polymorphisms
• Why Do Genetic Testing?
• Clopidogrel Genetics (Cont'd)
• Caveats — Other Reasons for Poor Response to Clopidogrel
• CYP2C19 Polymorphism May Require Another Factor
• Controversy for Clopidogrel
• Warning: Diminished Effectiveness In Poor Metabolizers
• What Does Warning Mean For Clinicians With Patients On Clopidogrel?
• FDA Answer
• More Questions
• Summary
• References
• Questions?
• Disclosure