Table III.

Physicochemical Characterization of Salt Forms of Prazosin

Property	PRB MES	PRB BSA	PRB CSA	PRB TSA	PRB OA	PRB MEA
Microscopy (optically polarized)	Crystalline	Crystalline	Crystalline	Crystalline	Crystalline	Crystalline
Melting point (onset °C)	267	316	332	300	254	237
Solid form	Monohydrate	Monohydrate	Anhydrous	Monohydrate	Dihydrate	Monohydrate
Hygroscopic behavior (92% RH)	<1% weight gain (nonhygroscopic)	<1% weight gain (nonhygroscopic)	<1% weight gain (nonhygroscopic)	<1% weight gain (nonhygroscopic)	<1% weight gain (nonhygroscopic)	Converts to dihydrate
Aqueous solubility (mg/ml)a	1.57 (hydrate)	0.41 (hydrate)	0.22 (anhydrous)	0.28 (hydrate)	0.16 (hydrate)	0.14 (hydrate)
pH (aqueous saturated solution, 37°C)	4.45–4.50	5.55–5.60	5.55–5.60	5.50–5.55	3.30–3.35	5.90–5.95
Photostability; color after photostability	92.6 (2.76); orange	78.39 (4.31); orange	94.25 (0.08); creamy white	87.11 (0.05); orange	76.84 (0.02); orange	85.30 (3.04); orange

^aAqueous solubility determined after 24 h (parentheses indicate the polymorphic form of the solid obtained after the solubility study)