[Theophylline semi-solid matrices containing polyethyleneglycols. 3--Mechanism of release].

Some rheologic mesures made on a PEG range ranking from PEG 300 to PEG 6000 and containing, as a theophylline plot indicate an expected result: the viscosity increases with the molecular mass of the polymer. These same measures made on a binary mixture of PEG composed of 95% PEG 300, liquid, and 5% of solid, thickening, make appear the peculiarity of the binary mixtures of PEG: the viscosity of the binary mixture of PEG is higher than the one of the solid PEG. This "paradoxical" viscosity results, apparently, on one side from the concomitant translation and opposed of the respective points of vitrous transition of the vehicle (liquid PEG) and of the thickening (solid PEG); and on the other side, of the different solidifications of the chains of different polymers forming the binary mixture.

[Kinetics of liberation of the theophylline in semi-solid matrix based of Gelucire].

Dissolution of a tracer included in Gelucire is primarily governed by two physico-chemical nominative parameters of this auxiliary substance which are its melting point and its hydrophily-lypophily balance. As they are not dissociable and their interaction is very significant, the optimisation of a formulation containing a mix of Gelucire cannot be done with polynomial models. An indirect modelisation, as Simplex, is however possible.

[Modeling the kinetics of theophylline release from a semi-solid matrix: Gelucire].

Controlling release of a trace is an indispensable pharmacological technique. Release of the active substance can be modulated to meet the desired kinetic requirements of the formulation by carefully choosing the excipient and controlling the solubility of the tracer. We studied the preformulation of a semi-solid matrix, Gelucire, to examine the kinetic properties of theophylline release.