title: The role of polymer concentration on the molecular mobility and physical stability of nifedipine solid dispersions.
abstract: We investigated the influence of polymer concentration (2.5-20% w/w) on the molecular mobility and the physical stability in solid dispersions of nifedipine (NIF) with polyvinylpyrrolidone (PVP). With an increase in polymer concentration, the α-relaxation times measured by broadband dielectric spectroscopy were longer, which reflects a decrease in molecular mobility. In the supercooled state, at a given temperature (between 55 and 75 °C), the relaxation time increased linearly as a function of polymer concentration (2.5-20% w/w). The temperature dependence of the relaxation time indicated that the fragility of the dispersion, and by extension the mechanism by which the polymer influences the relaxation time, was independent of polymer concentration. The time for NIF crystallization also increased as a function of polymer concentration. Therefore, by using molecular mobility as a predictor, a model was built to predict NIF crystallization from the dispersions in the supercooled state. The predicted crystallization times were in excellent agreement with the experimental data.
authors.affiliation: †Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota 55445, United States.
authors.forename: Khushboo
authors.initials: K
authors.lastname: Kothari
authors.affiliation: †Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota 55445, United States.
authors.forename: Vishard
authors.initials: V
authors.lastname: Ragoonanan
authors.affiliation: †Department of Pharmaceutics, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota 55445, United States.
authors.forename: Raj
authors.initials: R
authors.lastname: Suryanarayanan
mesh_terms: D003460:Crystallization; D004355:Drug Stability; D009543:Nifedipine / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D011205:Povidone / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D011108:Polymers; D011205:Povidone; D009543:Nifedipine
keywords: X-ray powder diffractometry; crystallization; dielectric spectroscopy; molecular mobility; nifedipine; polyvinylpyrrolidone (PVP); solid dispersion