Two galactomannans and scleroglucan as matrices for drug delivery: preparation and release studies.

Two galactomannans, Guar gum and Locust bean gum, have been used as matrices for tablets to study the release of model molecules. As a comparison, matrices obtained with another polysaccharide, Scleroglucan, have been tested. Despite the different conformations that the polymers assume in aqueous solution (flexible coils for Guar gum and Locust bean gum; triple helix for Scleroglucan), when prepared as tablets, they show (in distilled water and at 37 degrees C) very similar release profiles of guest molecules (i.e. theophylline, vitamin B12 and myoglobin) of different steric hindrance. Furthermore, the polymers were chemically crosslinked with glutaraldehyde to obtain a network suitable as a matrix for modified drug release. The delivery of the model molecules from the Guar gum and Locust bean gum gels, and from tablets prepared from the freeze-dried hydrogels of the three polymers was evaluated, and a comparison with the tablets prepared with the not-crosslinked polymers was carried out. Experimental data showed how the presence in the matrix of a well-defined network, by introducing a spacer among the macromolecular chains, always increased the rate of delivery of the tested molecules in comparison to the release profiles obtained when no crosslinker was present. Release data from the tablets were analyzed according to a mathematical model able to determine the relative importance of drug dissolution and drug diffusion on the overall release kinetics. Good agreement was found between the simulated and the experimental data.