Influence of crosslinked alginate on drug release from highly concentrated emulsions

Biocompatible water-in-oil (W/O) and oil-in-water (W/O) highly concentrated emulsions (HIPREs) have been formed at 25 degrees C, in systems consisting of aqueous component/castor oil derivative surfactant/oil compound. In both kinds of emulsions the concentration of internal phase was 83% and the aqueous component consisted of water, 1% sodium alginate solution or a mixture of sodium alginate solution and calcium chloride solution (crosslinked calcium alginate). Ketoprofen (KP) or clindamycine hydrochloride (CH) were solubilized in both kinds of HIPREs and the influence of the composition of the aqueous phase on drug release was studied. Droplet sizes of the W/O HIPREs formed were in the nanometric range, being smaller than other HIPREs described in the literature. Dynamic viscoelastic measurements showed an increase in the elastic modulus (G') of the emulsions in the presence of alginate or crosslinked alginate. The influence of the order of incorporation of alginate and calcium chloride on the viscosity was demonstrated, as an indication of crosslinking efficiency. KP release to a PBS receptor solution was slower when crosslinked alginate was formed in the internal phase of W/O HIPREs. In contrast, the influence of crosslinked alginate on the release of CH was negligible and the solubility of the drug in the disperse phase demonstrated to be the main mechanism responsible of CH diffusion. The results obtained suggest that the formation of a crosslinked alginate matrix in the internal phase of HIPREs is a factor that has to be taken into account in the development of controlled drug delivery systems.