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Analytical Control
Systems, Inc Analytical Control Systems, Inc. |
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317-841-0458
317-841-3186
Analytical Control Systems, Inc.
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Platelet Aggregometry Assay (PAA™) and Reopro® Abciximab (Reopro®) Platelet Inhibition Is Inversely Related to Platelet Concentration as Monitored by the Platelet Aggregometry Assay (PAA™) By KA Schwartz*, DE Schwartz*, EJ Gregoire* and JM Davis*. * Michigan State University, East Lansing MI. First presented in 1998 at the American Society of Hematology Meeting as a Poster and Abstract. Abstract: The anti-IIb/IIIa monoclonal antibody, Abciximab (Reopro®) is effective in preventing recurrence of coronary arterial occlusion following angioplasty. However, with doses that block 100% of the platelet receptors, patients may experience increased hemorrhage. If emergency by-pass surgery is required while patients are receiving Abciximab, patients are at a high risk for severe surgical bleeding. Abciximab doses that do not block 100% of the platelet receptors may be just as effective in preventing recurrence of vessel occlusion and may not produce increase hemorrhage, hence, the need to quantitate the platelet inhibitory effects of Abciximab. Since Platelet Aggregation Assay (PAA) (Analytical Control Systems, Inc.) used as an agonist can detect and clearly separate aspirinated platelets from normal platelets, we used the PAA™ to test two hypotheses: 1) that PAA™ will detect the inhibition of platelet function produced by Abciximab and 2) that platelet inhibition produced by Abciximab will be increased with lower platelet concentrations. Platelet rich plasma obtained from ten normal donors was adjusted to 100,000, 200,000 and 300,000 platelets/uL and incubated at room temperature for 1/2 hour with 1.3ug/mL of Abciximab. The concentration was calculated to occupy approximately 75% of the platelet receptors at 100,000 platelets/uL using an Abciximab-labeled radioimmunoassay. Using 30uM PAA™, Abciximab inhibition of platelet function, as measured by the time to 50% aggregation, was inversely related to platelet concentration. We conclude that: 1) PAA™ detects the platelet inhibition produced by Abciximab, and 2) the inhibitory effect of Abciximab is dependent on platelet concentration, with increased platelet inhibition observed with lower platelet concentrations. These results support the hypothesis that incorporation of platelet count in the dosing calculations would lead to better control of platelet inhibitory effects produced by Abciximab.
Introduction: The monoclonal antibody Abciximab (Reopro®) inhibits platelet function by binding to the platelet IIb/IIIa glycoprotein. Fibrinogen attachment to the platelet IIIa glycoprotein is blocked resulting in decreased platelet related hemostasis. Abciximab is commonly used following angioplasty to inhibit recurrence of coronary artery occlusion. The dose of Abciximab is calculated according to the person’s weight and blocks over 95% of the available platelet binding sites to produce a profound defect in platelet function. If emergency open heart surgery is required following Abciximab therapy, the surgical bleeding may be uncontrollable. It may be possible to tailor the dose of Abciximab to produce the optimal amount of platelet inhibition that will inhibit vessel occlusion and not the increase the patient’s risk for severe bleeding. Platelet Aggregation Assay (PAA) stimulates platelet aggregation. When tested as a platelet agonist using a standard platelet aggregometer, PAA detected the aspirinated platelet with a sensitivity of 100 percent. Using the Platelet Aggregation Assay (PAA™), we investigated the hypothesis that:
In addition, the ability of PAA™ to detect the additional platelet inhibition produced by Abciximab in aspirinated platelets was investigated.
Methods: Abciximab was radio-labeled with 125-I and used to develop a dose response curve to calculate the dose of Abciximab that bound approximately 75% of the receptors at 100,000 platelet/uL. The PAA™ was performed on a Chrono-Log Platelet Aggregometer. 30uM PAA was added to the appropriate concentration of platelets and the slope of the aggregometry curve and the time to 50% maximal aggregation were measured. At a dose of Abciximab calculated to saturate approximately 75% of the platelet receptors, the amount of platelet inhibition was measured on platelets from 10 normals using the PAA™ at three different platelet concentrations (100,000, 200,000 and 300,000/uL). After obtaining informed consent, blood was obtained immediately before and 5 minutes after 4 patients were given Abciximab. Abciximab induced platelet inhibition was evaluated using the PAA.
Conclusions:
These results support the hypothesis that incorporating platelet counts into the dosing calculations for Abciximab would lead to better control of the amount of platelet inhibition.
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