Thursday, September 16, 2010

Optical Platelet Aggregation drug monitoring for P2Y12 inhibitors (e.g. Plavix or Clopidogrel)

Due to a number of inquiries concerning the monitoring of platelet inhibitors used in cardiovascular procedures, such as percutaneous coronary interventions (PCI), we would like to call your attention to some studies in this area and what we do to answer the concerns of physicians to monitor the effectiveness of the drugs currently used to reduce the incidence of non-responders to the therapy.  Current recommendations for PCI are to use Clopidogrel (Plavix) and Aspirin prior to and post procedurally to inhibit platelets from coagulating in the newly inserted stents. There is a high incidence of  patients who do not respond well to these inhibitors and we can differentiate them from the normal responders using a classical thoroughly validated technique, known as Optical Platelet Aggregation or Platelet Function analysis. Other techniques have been used and their problems have been discussed in the paper cited below along with a comparison with the classical method of Optical Platelet Aggregation (OPA). This paper compares a population study of 530 patients undergoing PCI and studied using the techniques of OPA, Verify Now and PFA-100. It evaluated the parameters that influenced the determination of who responded and who didn’t respond to the therapy (e.g. age, gender, inflammation, BMI, Diabetes and malignancy which are typical aspects seen as variables with OPA). It noted unexpected variables seen with the Verify Now P2Y12 analyzer of hematocrit and hemoglobin levels, while the PFA was influenced by B-blockers.

I would also like to mention that  “P2Y12” is the  name of the membrane glycoprotein that is specifically inhibited by Plavix and affects the platelet’s response to ADP, an agonist used in OPA to monitor platelet aggregation. Aspirin is also monitored in platelet aggregation by using the agonist Arachidonic acid. To confuse the story a little more, the researchers have coined the term “High Responders” referring to the fact that patients are poor responders to the drugs or their platelet are still reactive to the ADP or Arachidonic Acid agonists.

The reference I refer you to is in the Journal of Haemostasis and Thrombosis, 2009,102:719-727.  The Influence of Clinical Characteristics, Laboratory and Inflamatory Markers on “High on Treatment Platelet Reactivity” as Measured with Different Platelet Function Tests.
Ellen H.A.M. Elsenberg, Jochen W van Werkum, Ruud M.A. van de Wal, A.Carla, Zomer, Heleen J. Bouman, Freek W.A. Verheugt, Jurrien M. ten Berg, Christian M. Hackeng.

In conclusion, if anyone asks for P2Y12, Plavix or Clopidogrel monitoring, we do it daily with an order of a Platelet Function Analysis, same day turn around time and the whole blood samples (3-4 Blue top tubes) should be sent with 2 hours of the phlebotomy at room temperature. Please make a note of the type of medications the patient is on so that our comments can be specific as to their response.

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