Roland S. Okor

Effect of humidity on the disintegrant property of α-cellulose, Part II: A technical note

ConclusionThe summary is that the high humidity impaired the disintegrant property of α-cellulose in all 3 tablets tested. Tablets of aspirin, which is the more hygroscopic drug, were also more sensitive to the humidity effect, while tablets of chloroquine phosphate, which is a water-soluble drug, were the least sensitive to the humidity effect. The results permit the conclusion that moisture uptake with subsequent gelling of the α-cellulose is the mechanism of impairment of its disintegrant property. The tablets would not normally be stored under an RH as high as 100%, nevertheless, the results of the accelerated stability study have underscored the need to protect tablets containing α-cellulose as disintegrant from moisture.

The effect of phenol on the electrolyte flocculation of certain polymeric dispersions to thixotropic gels

Aqueous dispersions of an acrylate-methacrylate, a water-insoluble copolymer, were prepared by a coacervation technique. Addition of sodium chloride (0.2 M) to the dispersion (10%, w/v) converted the system to a thixotropic gel which turns fluid on shaking and reverts to gel on standing. Phenol (0.03 M) inhibited the gelling effect of the electrolyte. Among the various phenolic compounds tested, phenol displayed the strongest and chlorocresol the weakest antigelling property. Sodium chloride reduced the electropotentials (index of particle–particle repulsiveness) of the polymer dispersions, while phenol increased the potentials. It is thought that the phenol solution acted as a dielectric which increased the interparticle repulsive potential, hence its antiflocculant effect.

Structure and permeability of composite films of two analogous acrylate methacrylate copolymers

Two analogous acrylate methacrylate copolymers, A and B, which form films with compact surface zones (skins) have been layered into composite films AB and BA. Electron micrographs of the composite film internal structure revealed a porous asymmetry; the mean pore size in layer A was 2.4 ± 0.3 µm, and that in layer B 0.71 ± 0.06 µm. The actual surface pores were considerably smaller than the internal pores, below the limit of resolution of the electron microscope. AB (layer A accepting the permeant first) was 17 times more permeable to the solute, urea, than BA. Exposure of the film surfaces to solvent vapor before layering caused dissolution of the “skin” in component layers; resulting composite films were therefore more permeable than theoretical expectation.

Effect of Protective Coating of Aspirin Tablets with Acrylatemethacrylate Copolymers on Tablet Disintegration Times and Dissolution Rates

Tablets of aspirin (a moisture degradable drug) have been film coated with two analogous Eudragit RL and RS copolymers designated here as A and B which differ only in their cation content in the ratio 2:1 (A:B). A, is therefore more hydrophilic than B. The tablets were film coated with ethanol solutions of these two polymers. Film coating with either A or B significantly reduced the moisture uptake potentials of the tablets but caused an increase in the disintegration times of the tablets and retarded dissolution rates. The mean disintegration times were 0.5±0.1 min (uncoated tablets), 16±2.5 min (tablets coated with A) and 115±3.6 min (tablets coated with B). The corresponding dissolution rates % h -1 were 28.3 for uncoated, 16.6, coated with A and 14.8, coated with B, respectively. Thus, coating with polymer B considerably impaired the disintegration and dissolution properties of the tablets.

Solute Permeability of Certain Polymeric Films Applied on Aspirin Crystals to Form Microcapsules

A study was carried out to investigate the solute permeability of various polymer films applied on aspirin crystal to form microcapsules. The coating materials were an acrylate methacrylate (AMA), poly 3‐hydroxybutyrate‐hydroxyvalerate (Biopol®) and poly (lactic‐glycolic) acid (PLGA). Organic solutions of the polymers were applied on the aspirin crystals (core) by a spray coating technique in a Wurster column. The microcapsule surfaces were investigated using scanning electron microscopy (SEM), while permeability studies were carried out on single microcapsules serving as micro dialysis cells. The amount of drug (m) permeating through the applied films in time (t) was analysed on the basis of Fickian diffusion. The SEM revealed numerous surface pores of size range 2.4 to 24 μm for the AMA films, while the PLGA and Biopol films, on the other hand, exhibited very few surface pores of size range 2.2 to 18 μm. However, the AMA films were more spongy than the PLGA and Biopol. The AMA films displayed a retarded release while the PLGA or Biopol films displayed a burst release, attributable to the differences in the films porous structure. The Permeability coefficient (P) depended on the core weight of the single microcapsules, decreasing with increase in core weight. Thus, for an ensemble of the microcapsules the permeability coefficients of the films of the component microcapsules will have a distribution of P values even though the coating material is the same. This finding is important in the simulation of drug release from coated multiparticulate systems.