title: Modeling of drug release from partially coated matrices made of a high viscosity HPMC.
abstract: A mathematical model able to describe the release kinetics of two model drugs (Diprophylline and Theophylline) from partially coated hydroxypropylmethylcellulose (HPMC, Methocel) K4M) matrices is presented. As solvent interaction with the system and drug release can only take place in one direction, the physical frame to be modeled turns out simpler. The model was developed starting from the established equation describing drug dissolution and taking into account the resistance to drug release given by the presence of a growing gel barrier around a matrix system. The model fits the release data obtained from both series of hydrophilic matrices containing increasing amounts (from 0.2 to 0.8 mass ratio) of the two xanthine derivatives. Differences were found in drug release rate according to the different solubility of the actives. Interestingly, however, there is no further reduction in the outer gel layer permeability when the polymer mass fraction exceeds a certain value, with both Theophylline and Diprophylline systems. Results confirm the importance of the fraction of the glassy/rubbery interface held by the active substance in defining the release rate from hydrophilic systems.
authors.affiliation: Department of Chemical, Environmental and Raw Materials Engineering, DICAMP, University of Trieste, Piazzale Europa 1, 34127 Trieste, Italy. mariog@dicamp.univ.trieste.it
authors.forename: Mario
authors.initials: M
authors.lastname: Grassi
authors.forename: Lucia
authors.initials: L
authors.lastname: Zema
authors.forename: Maria Edvige
authors.initials: ME
authors.lastname: Sangalli
authors.forename: Alessandra
authors.initials: A
authors.lastname: Maroni
authors.forename: Ferdinando
authors.initials: F
authors.lastname: Giordano
authors.forename: Andrea
authors.initials: A
authors.lastname: Gazzaniga
mesh_terms: D016503:Drug Delivery Systems; D004400:Dyphylline / Q000008:administration & dosage* / Q000493:pharmacokinetics; D065347:Hypromellose Derivatives; D008747:Methylcellulose / Q000031:analogs & derivatives; D008962:Models, Theoretical; D013607:Tablets; D013806:Theophylline / Q000008:administration & dosage* / Q000493:pharmacokinetics; D014665:Vasodilator Agents / Q000008:administration & dosage* / Q000493:pharmacokinetics
chemical_list: D013607:Tablets; D014665:Vasodilator Agents; D004400:Dyphylline; D065347:Hypromellose Derivatives; D008747:Methylcellulose; D013806:Theophylline