The effect of charges on permeabilities of drugs through collagen membranes

Examination of self-crosslinked gelatin as a hydrogel for controlled release

A gelatin matrix crosslinked by extensive dehydration was examined for use in controlled drug delivery in this preliminary investigation. Crosslinking is necessary to prevent gelatin dissolution and immediate drug release at body temperature. Treatment at 105 degrees C and reduced pressure induced crosslinking in discs prepared from Type B gelatin. Crosslinking was evaluated by determining changes in gelatin solubility at 37 degrees C in a USP paddle dissolution apparatus. The crosslinking treatment was reproducible and resulted in 90% of the original gelatin mass remaining after 12 h in water and in phosphate buffer solutions of pH 3 and 6.4. The treated gelatin discs remained intact for greater than 24 h at pH 6.4. Chlorpromazine.HCl (CPZ) was incorporated as a model drug by soaking the treated gelatin discs in an aqueous solution of the drug. Release of CPZ at 37 degrees C in the dissolution apparatus was fitted to an empirical equation. A coefficient of this equation was used as the initial release rate for comparison between different release profiles. The roles of drug solubility, matrix swelling and erosion, and potential drug-matrix interactions were examined by conducting release studies at pH values of 3, 4, 6.4, and 7.4. The insoluble, un-ionized form of the drug had the slowest release rate. The soluble, ionized form under conditions of maximum swelling and a possible drug-matrix repulsive interaction had the fastest release rate. General electrostatic drug-matrix interactions were noted which could influence the drug release rate depending on conditions of the study. The times for 50% release of CPZ ranged from 1.8 to 11.3 h.

Inclusion complexation of warfarin with cyclodextrins to improve some pharmaceutical characteristics

Inclusion complexation of warfarin and alpha- or beta-cyclodextrins in water and in the solid phase were studied by a solubility method, a membrane permeation study, thin-layer chromatography, a dissolution study, IR spectroscopy and differential scanning calorimetry. The solubility of warfarin increased with the addition of cyclodextrins. The apparent stability constants of the alpha- and beta-cyclodextrin complexes are 10.29 M-1 and 148.88 M-1, respectively. The greater the stability constant of the inclusion complex the lesser the permeability of warfarin. Solid complexes of warfarin and alpha- or beta-cyclodextrins were obtained by freeze-drying. Clear differences in IR absorption spectra and DSC thermograms were observed between the inclusion complexes and physical mixtures. The dissolution rate of the freeze-dried warfarin-cyclodextrin complexes was increased about 1200-fold and 550-fold for alpha- and beta-cyclodextrins, respectively. The dissolution rate of warfarin was significantly improved by complex formation.

Release characteristics of dibucaine dispersed in konjac gels

A possible use of konjac gel for sustained release of drugs was examined in a monolithic system containing dibucaine. Dibucaine was dispersed in the gel which was prepared by gelation of the konjac flour in a borax solution at 60 degrees. The cumulative amount of the drug released plotted against the square root of time was linear in the monolithic system. This relationship was in agreement with that expected from the theoretical equation for planar configuration. The mechanism of the release of the drug from the gel may be considered to be leaching of the drug by the permeating fluid. The release profile from dried konjac gel was similar to that from undried gel, but that from unwarmed gel showed a deviation from linearity although sustained release was similarly obtained.