INGREDIENT RELEASE FROM AEROSOL FILMS 675 • 4 2 l0 [ Figure 1. Schematic diagram of apparatus used to measure drug release rates from polymeric films. Key: 1. Glass-stoppered tube 2. Test film 3. Thermometer 4. Desorbing solvent 5. Magnetic stirring bar 6. Water-jacketed glass beaker 7. Magnetic stirrer 8. Inlet for water jacket 9. Outlet for water jacket 10. Constant-temperature water bath equipped with circulating pump the absorbance had been measured in order to maintain a constant volume. To evaluate the effect of electrolytes on the rate of release, the determinations were made in 0.45% sodium chloride solution in water, 0.45% sodium sulfate solution in water, and potassium phosphate buffer in pH 7. The release was noted over a period of about 10 hours. The kinetics of the release of Gentian Violet was studied using the film-formers previously indicated with the exception of Ethyl Cellulose N-10. A satisfactory film could not be obtained in the presence of Gentian Violet. Additional studies are indicated to determine the reasons for this behavior. Determination of Initial Drug Concentration (.4o) of the Film The initial concentration of Gentian Violet in the film was deter- mined spectrophotometrically by dissolving the film in isopropanol. The results of the release of Gentian Violet from various films using several desorbing solutions are shown in Figs. 2--4 and represent the average of

676 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS x 49 ß Z 0 47 ß Z k) 46 Z 0 1 2 3 4 :5 6 7 8 9 10 TIME, hr Figure 2. Releasc of Gentian Violet into different solvents (Emerez 1533 film containing hexadccyl alcohol, 10% w/w). ß Desorbing solvent, 0.4,5% sodium chloride solution [] Desorbing solvent, 0.45% sodium sulfate (anhyd.) solution * Desorbing solvent, potassium phosphate buffer solution pH 7 two determinations for each film. Log plots were constructed in order to determine the kinetics of the release from the films. DISCUSSION OF RESULTS It is evident from the data presented related to the effect of plasti- cizer on the nature of films that the modulus of elasticity tends to de- crease with increasing amount of plasticizer, while flexibility increases within the limits of optimum concentration of the plasticizer. Beyond the limits ot5 this optimum value, both flexibility and modulus of elas- ticity o15 the films decrease as the amount o15 plasticizer is increased. While trying to achieve the desired flexibility o15 the films, some loss of tensile strength should be anticipated. In the case of Ethyl Cellulose N-10, the incorporation o15 plasticizer in the film enhances the flexibility but decreases the hardness and modulus o15 elasticity o15 the films. With Emerez 1540, a marked decrease in both the flexibility and modulus o15 elasticity was observed as the amount o15 plasticizer in the film exceeded the optimum concentration.