Abstract: Described is a highly stable crystalline form of bosentan having a water content in the range of about 3-4% by weight, based on the total weight of the bosentan, (bosentan crystalline form A5), a process for preparation thereof, and pharmaceutical compositions comprising the bosentan crystalline form A5. Provided also herein is a bosentan impurity, p-tert-butyl-N[6-hydroxy-5-(2-methoxyphenoxy)-2-(2-pyrimidinyl)-4-pyrimidinyl]benzenesulfonamide (deshydroxyethyl bosentan impurity), and process for preparing and isolating thereof. Further provided are highly pure bosentan or a pharmaceutically acceptable salt thereof substantially free of deshydroxyethyl bosentan and bosentan dimer impurities, process for the preparation thereof, and pharmaceutical compositions comprising solid particles of highly pure bosentan or a pharmaceutically acceptable salt thereof, wherein 90 volume-percent of the particles (D90) have a size of less than about 300 microns.

Abstract: Disclosed herein are novel polymorphic forms of bosentan, processes for preparation, pharmaceutical compositions, and method of treating thereof.