Since antiplatelet therapy has become a key component in cardiovascular and neurovascular medicine, it is important to monitor the effectiveness of these medications. Recent studies have demonstrated an emergence of the new clinical entity of "clopidogrel resistance," also referred to as clopidogrel nonresponsiveness. Clopidogrel is marketed under the trade name, Plavix®. Studies have shown that as many as 30% of patients do not respond adequately to standard doses of clopidogrel (similar to the statistics in aspirin resistance).
There are several possible mechanisms of clopidogrel resistance, including:
- Genetic variants that alter or inhibit appropriate clopidogrel metabolism
- Noncompliance in taking clopidogrel as prescribed
- Interference from other medications
- Accelerated platelet turnover, with introduction into bloodstream of newly formed, drug-unaffected platelets that can negatively influence antiplatelet effect of clopidogrel
Age, diabetes mellitus, decreased left ventricular function, renal failure, and acute coronary syndrome are all associated with decreased clopidogrel function.