Rafigrelide is an imidazoquinazoline derivative patented by pharmaceutical company Shire LLC as platelet-lowering agent for the treatment of myeloproliferative diseases. Rafigrelide is a chemical analog of anagrelide, which is used to reduce platelet counts in myeloproliferative disorders. Compared with anagrelide, Rafigrelide has reduced potency against phosphodiesterase III, which may help to reduce potential side effects. The concentration of Rafigrelide that produces 50% of the maximum inhibition (IC50) of PDE III is 164 nM, making it an approximately 200-fold less potent inhibitor of phosphodiesterase III than 3-hydroxy anagrelide. In the clinical trial, Rafigrelide showed antithrombotic properties during a two-week treatment period in healthy male volunteers. The reductions in thrombus formation were seen in surrogate models of both high and low shear rates suggesting drug efficacy in different arterial conditions.