title: Effect of surface characteristics of theophylline anhydrate powder on hygroscopic stability.
abstract: The hygroscopicity of theophylline anhydrate has been investigated by gas adsorption and hydration kinetic methods. Type 1 theophylline anhydrate was obtained by recystallization from distilled water at 95 degrees C, and type II was obtained by dehydration of theophylline monohydrate. The X-ray diffraction pattern of types I and II agreed with the data of theophylline anhydrate. However, the diffraction peaks of the (200) and (400) planes of type I were much stronger than those of type II. The particles of type I were clear crystalline-like single crystals. However, the particles of type II had many cracks. The gas affinity balance (H/N) of type II, measured by gas adsorption, was about 7 times that of type I. After the hygroscopicity of types I and II had been tested at various levels of relative humidity (RH) at 35 degrees C, type I was stable at less than 82% RH, but transformed into the monohydrate at more than 88% RH. Type II was stable at less than 66% RH and transformed into the monohydrate at less than 75% RH. The hydration data of type I at 88% RH and type II at 75% RH were calculated for hydration kinetics using various solid-state kinetic models, but no particular model could be preferred from these data.
authors.affiliation: School of Pharmaceutical Sciences, Showa University, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Otsuka
authors.forename: N
authors.initials: N
authors.lastname: Kaneniwa
authors.forename: K
authors.initials: K
authors.lastname: Kawakami
authors.forename: O
authors.initials: O
authors.lastname: Umezawa
mesh_terms: D000327:Adsorption; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D003460:Crystallization; D004055:Differential Thermal Analysis; D004355:Drug Stability; D010316:Particle Size; D011208:Powders; D013055:Spectrophotometry, Infrared; D013499:Surface Properties; D013806:Theophylline / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D011208:Powders; D013806:Theophylline