Painful crisis represent the most common clinical problem in sickle cell disease, and are largely responsible for making the lives of these patients so unpredictable. However, the treatment of these painful crisis remains inadequate, consisting mainly of strong pain medications. In this study, we will evaluate the safety of eptifibatide in sickle cell patients and how well it works during the course of painful crises. At the completion of this trial, we will have an improved understanding of the contribution of platelet activation and inflammation to the problems in sickle cell disease.