The effect of drug loading on a scleroglucan gel matrix: a kinetic and dynamic rheological study.

FRANÇOIS N.J., ROJAS A.M. Y DARAIO M.E.

POLYMER INTERNATIONAL

John Wiley & Sons Ltd., publica para The Society of Chemical Industry (SCI).

Lugar: Baffins Lane, Chichester, Sussex PO19 1UD, England.; Año: 2005 vol. 54 p. 1613 - 1619

0959-8103

ABSTRACT It was analyzed the effect of drug (theophylline) loading level ranging from 0 to 0.40% w/w on the in vitro drug release kinetics and on the viscoelastic properties of a 2% w/w-scleroglucan gel-matrix. Storage (G’) and loss (G”) moduli as well as the tangent of the phase shift angle d (tand = G” / G’) were determined by oscillatory experiments carried out in a rheometer. Dynamic rheological parameters were compared with the release kinetic parameters of theophylline measured in the gel samples. It was found that when drug content changed from 0.04 to 0.06 % w/w, the tand-value increased in about 17% compared to that determined on the drug-free gel. This result was adjusted to a plasticizing drug-effect on the gel-netwok. Conversely, at 0.40% w/w of drug concentration, the lowest tand value was found, which was associated to an increase of the intermacromolecular links. In addition, the diffusional exponent obtained after fitting the data with a semi-empirical power law, changed from Fickian to non-Fickian drug transport mechanism in the 0.04% - 0.06% w/w-theophylline concentration range. It was suggested that the presence of drug at concentrations higher than 0.04% w/w determined a competition with Scl-macromolecules for water molecules, allowing the existance of two different effects. One prevailed over the other depending on the drug/polymer ratio of the gel-netwok.