Thermal Characterization Of The Amorphous Form Of Sulfapyridine-The Effect Of Humidity And Excipients

摘要

Sulfapyridine has been reported to exist in five polymorphic forms and one amorphousrnform. The high enthalpy and entropy properties of the amorphous form would result in enhancedrnsolubility of the amorphous form and therefore greater bioavailability. Differential ScanningrnCalorimetry (DSC) and Powder X-Ray Diffraction (PXRD) were extensively used throughoutrnthe study. This study was an effort to determine a protocol for the conversion of the crystallinern(commercial variety) to the amorphous form and then study the stability of the amorphous formrnwith common pharmaceutical excipients - microcrystalline cellulose (MCC) and magnesiumrnstearate (MgSt) at 10, 40 and 100% relative humidity (RH) conditions for a period of 20 days.rnAll DSC studies were carried out at a heating rate of 10℃/min with a nitrogen flow rate of 50rnmL/min. The amorphous form had a glass transition temperature between 55-60℃, a coldrncrystallization peak between 92-99℃, melting of the metastable form between 185-189℃rnfollowed by melting of the stable form between 191-193℃. The study revealed that thernamorphous form undergoes transition to the crystalline form at 100 and 40% relative humidityrnconditions but was stable at 10% relative humidity conditions for a 20 day exposure period. Thernamorphous form did not absorb any water under different humidity conditions suggesting thatrnthe presence of water alone, at >10 % relative humidity causes it to onvert from amorphous torncrystalline form. The excipients had no or little interaction with the drug and also had nornstabilizing action on the amorphous form.