NEW FORM III OF DOXAZOSIN MESYLATE

PROBLEM TO BE SOLVED: To obtain a crystalline anhydride of the subject compound useful for treating hypertension and benign prostomegaly, by taking a specific crystal form so as to be easily synthesizable, capable of realizing its high purity and water solubility, and also capable of advantageously producing solid preparations such as tablets or capsules. SOLUTION: This crystalline anhydride of doxazosin mesylate is in a form giving such power X-ray pattern as to have peaks of high or medium intensity at diffraction angles of 8.49 deg., 11.72 deg., 16.03 deg., 18.29 deg., 21.03 deg., 22.87 deg. and 25.02 deg., being obtained, for example, by the following process, that is, basic doxazosin is converted to doxazosin acetate by acetic acid in an organic solvent, the resultant solution is clarified in a hot state and then mixed with methanesulfonic acid followed by agitating the solution at a temperature ranging from 30 deg.C to the boiling point of the solvent; the resultant solvent adduct is collected through filtration, and, in a wet state, put into a lower alcohol, heated at the boiling point for 10min to 12hr, and then cooled to room temperature; and the resulting precipitated crystal is collected through filtration.