NEW FORM II 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 anhydrous 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 10.68 deg., 14.45 deg., 17.37 deg., 23.45 deg., 23.82 deg., and 24.30 deg., being obtained, for example, by the following process, that is, basic doxazosin A1 is suspended in a lower ketone followed by addition of a weak acid and, optionally, methanesulfonic acid A2 in an amount below equimolar level to form a water-soluble salt of A1 with the weak acid and/or a salt of part of A1 with A2 followed by adding A2 and a base to the system to adjust pH2-4 to effect precipitation of doxazosin mesylate, and the precipitate is collected through filtration, washed with an organic solvent, and then dried.