Effect of manufacturing procedures on the dissolution and human bioavailability of diphenylhydantoin

Enhancement of dissolution rate and anti-inflammatory effects of piroxicam using solvent deposition technique

Piroxicam solid depositions were prepared by means of the solvent deposition technique using different concentrations of microcrystalline cellulose as carrier material. The solvent deposition system (SDS) with drug to carrier ratio of 1:9 had a rapid dissolution rate in vitro. When this SDS was administered perorally to rats with a previous experimentally induced inflammation in their paws, it exhibited a pronounced anti-inflammatory action. X-ray diffraction and infrared (IR) spectroscopy showed no differences in the crystal state of piroxicam in SDS formulation and physical mixture of piroxicam and carrier. The increase in the dissolution rate and consequent enhancement of anti-inflammatory effect of piroxicam in SDS were attributed to the reduced particle size of drug deposited on the carrier and enhanced wettability of the particles brought about by the carrier.

Influence of pH on release of phenytoin sodium from slow-release dosage forms

Physicochemical factors influencing the release of phenytoin sodium from slow-release dosage forms were studied. Some of these factors were solubility and intrinsic dissolution rate as functions of pH, type of dosage form, pH of dissolution medium used, and conversion of the sodium salt to free acid (phenytoin). The innovator's product, Extended Phenytoin Sodium Capsule (Dilantin Kapseal, 100 mg, Parke-Davis), and two experimental formulations (one nondisintegrating tablet containing polymeric materials and the other a solid dispersion in an erodible matrix) served as the slow-release dosage forms. The sodium salt converts to practically insoluble phenytoin in the gastrointestinal pH range of 1 to 8. Due to such a conversion inside or at the surface of slow-release dosage forms, the release of drug in this pH range was incomplete. The extent of drug release also varied with the type of formulation used. In contrast, complete dissolution could be obtained in water because the pH of the medium gradually rose from approximately 6 to approximately 9.2 where the drug solubility was higher. Although several phenytoin sodium products might have similar dissolution rates in water, the extents of drug release under gastrointestinal pH conditions (pH 1-8) could differ greatly, thus supporting the Food and Drug Administration recognition that the similarity in dissolution profiles in water does not assure that the products are bioequivalent. The reported lower steady-state level of phenytoin in human plasma following oral administration of a slow-release dosage form may be related to incomplete drug release.