title: Comparison of the hanson microette and the Van Kel apparatus for in vitro release testing of topical semisolid formulations.
abstract: OBJECTIVE
  The major goal of this study was to compare the relative utility of the Hanson Microette and the Van Kel apparatus, two fully automated devices, as in vitro release tests (IVRT) for semisolids. We attempted to develop methodology that can be used to discriminate formulation changes, and to evaluate the precision, reproducibility and technical complexity of each test apparatus.
  
  
  METHODS
  We chose the sunscreen Eusolex 232 (2-Phenylbenzimidazole-5-sulfonic acid) as a model compound, which was incorporated into an emulsion formulation prepared in our laboratory. Test conditions for the two IVRT were made as nearly identical as possible, in order to obtain an accurate comparison.
  
  
  RESULTS
  The formulations were tested and found to be physically stable throughout the entire study. Diffusion coefficients were apparatus-dependent but were independent of the drug concentration in the formulations. The IVRT data were plotted as amount released (microg/cm2) vs. square root of time (s(0.5)) and a linear relationship was obtained in each case. Both methods produced similar results and were able to detect changes in drug loading in the formulations.
  
  
  CONCLUSIONS
  The linear relationship between the amount released and the square root of time indicates a diffusion-controlled release of drug. Both apparatuses proved to be suitable as tests for formulation " sameness" according to the FDA's SUPAC-SS guidelines, during level 3 changes. However, each apparatus produced a different release profile for the drug. The choice of apparatus will depend upon a number of considerations.
authors.affiliation: Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721 USA.
authors.forename: M
authors.initials: M
authors.lastname: Rapedius
authors.forename: J
authors.initials: J
authors.lastname: Blanchard
mesh_terms: D000287:Administration, Topical; D000465:Algorithms; D002626:Chemistry, Pharmaceutical / Q000295:instrumentation*; D002851:Chromatography, High Pressure Liquid; D004058:Diffusion; D004355:Drug Stability; D007700:Kinetics; D008567:Membranes, Artificial; D015203:Reproducibility of Results; D013056:Spectrophotometry, Ultraviolet
chemical_list: D008567:Membranes, Artificial