LabMed

Platelet Function Disorder Produced by Glycoprotein IIb/IIIa Inhibitors

At a Glance

Glycoprotein IIb/IIIa inhibitors in clinical use include tirofiban (Aggrastat), eptifibatide (Integrilin), and abciximab (ReoPro). These compounds are very potent antiplatelet agents. They are commonly used in procedures involving cardiac catheterization. In a small percentage of cases, these drugs can also induce a significant thrombocytopenia, with platelet counts often less than 10,000 per micrometer. Inhibition of platelets with glycoprotein IIb/IIIa inhibitors involves a different mechanism from that produced by aspirin, NSAIDs, such as ibuprofen, Plavix, and Prasugrel. Therefore, treatment of patients with glycoprotein IIb/IIIa inhibitors, along with other antiplatelet agents, commonly produces highly significant platelet inhibition that predisposes the patient to major bleeding.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Unlike other platelet inhibitors, particularly clopidogrel (Plavix), to which some patients do not respond and, therefore, may require a platelet function study to determine if the drug is working, it would be extremely rare to require documentation of platelet inhibition by glycoprotein IIb/IIIa inhibitors.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

If a patient experiences severe thrombocytopenia on exposure to a glycoprotein IIb/IIIa inhibitor, bleeding in association with the use of this compound may be a result of both an adequate platelet number and a defect in platelet function produced by the drug.

What Lab Results Are Absolutely Confirmatory?

If there is any reason to suspect a glycoprotein IIb/IIIa inhibitor is not inhibiting platelet function, any of the variety of platelet function studies available should determine whether the drug is effective.

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