[Theophylline semi-solid matrices containing polyethyleneglycols. 3--Mechanism of release]. / Matrices semi-solides de théophylline à base de polyéthyleneglycols. 3--Mécanisme de libération.

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.

[Semisolid theophylline matrices containing polyethyleneglycols. 2. Determination of molecular mass of the binary PEG]. / Matrices semi-solides de théophylline à base de polyéthylèneglycols. 2. Détermination des masses moléculaires des PEG binaires.

Previous work on the kinetics of theophylline release from semi-solid matrices based on PEG demonstrated that binary PEG mixes enable significant dissolution associated with strong viscosity. The present work was aimed to explain this singular property and indicated that the "virtual" mass of binary PEG is close to 2500-3000 and that theophylline release from semi-solid matrices based on PEG is not associated with vehicle mass, i.e. PEG, but rather with another independent latent variable.

[Kinetics of liberation of the theophylline in semi-solid matrix based of Gelucire]. / Optimisation de la cinétique de dissolution de la théophylline en matrices semi-solides de Gélucire.

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.

[Feasibility study of semi-solid matrices of theophylline-containing polyethyleneglycols]. / Matrices semi-solides de théophylline à base de polyéthylèneglycols.

Pharmaceutical manufacturing of semisolid matrices a past meeting two requirements: sufficient fluidity and sufficient viscosity. Ideally, the paste should have strong viscosity associated with a high dissolution rate. We studied the correlation between the viscosity and dissolution rate of polyethylene glycol (PEG) semisolid matrices (SSM) enclosing theophylline as a tracer. Nine formulations containing PEG of different molecular masses were studied. This work revealed the singularity of PEG binary mixtures. For pharmaceutical manufacturing, the conclusion of this work is that PEG binary mixtures enable circumventing the generally verified constraint: strong viscosity involves low dissolution ability.

[Modeling the kinetics of theophylline release from a semi-solid matrix: Gelucire]. / Modélisation de la cinétique de libération de la théophylline en matrices semi-solides à base de Gélucire.

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. Several models were analyzed. The results show that the formulation must be specific for the semi-solid matrix used.

Physicochemical and structural study of sulfamethazine.

We have shown by several physicochemical methods that the existence of different crystal habits for a given molecule does not necessarily imply polymorphism. For sulfamethazine, we found one polymorph, form 1, whose crystalline structure is published herein, and a methanol solvate.