ROSIN-BASED POLYMER AS CREAM BASE 205 release of drugs from 2.8 to 13.3 percent over the period of eight hours. The marketed preparation showed release of the drug from 2.2 to 13.6 percent. Thus the amount of drug released at the end of eight hours was similar for the marketed preparation and the cream containing polymer 2. This is also evident from a Student's t-test, which revealed that there is no statistically significant difference (p 0.01) in the overall release of the creams containing polymer 2 and that of the marketed cream. STABILITY STUDIES Dr•g content. The creams containing polymer 2 showed an initial drug content of 97.5 percent. After storage at 40øC and 50øC for 50 days, the drug content decreased to 97.2 percent and 97.0 percent, respectively. The creams containing Tween 60 showed an initial drug content of 97.7 percent. After storage at 40øC and 50øC for 50 days, the drug content decreased to 97.5 percent and 97.0 percent, respectively. The marketed preparation showed an initial drug content of 97.8 percent. After storage at 40øC and 50øC for 50 days, the drug content decreased to 97.5 percent and 97.3 percent, respec- tively. This indicates that the stability of the active ingredient in creams is reasonably satisfactory. pH. The pH of the creams ranged from 6.0 to 7.0, which is the normal pH range of skin. Particle size. The changes in particle size of the creams during storage are presented in Figure 2. The particle size data is in good agreement with all the other parameters tested for the stability of the creams. As shown in the figure, the particle size increased more in the case of creams containing Tween 60 and stored at 40øC and 55øC. The slight 25 20 15 10 i i i i I 14 28 42 -4• Room temperature • Room temperature --A-- 4OøC. i•T ß 55ø0 RT • 55øC • Time (Days) Figure 2. The changes in particle size of the prepared creams during aging. RT: cream with Tween 60. R2: cream with polymer 2.

206 JOURNAL OF COSMETIC SCIENCE change in the particle size in creams containing polymer 2 upon storage at various temperature ranges again gives evidence of good stability of this cream as compared to cream prepared with Tween 60. Conductivity and relative dielectric constant. The conductivity behavior of all the creams is shown in Figure 3. The formulations containing polymer 2 showed an increase in conductivity upon exposure to higher temperature. This may be due to the anionic nature of the polymer 2 itself, which shows an enhanced conductivity at higher tem- peratures. The changes in relative dielectric constant of the various creams are shown in Figure 4. The creams containing polymer 2 showed a slight change in relative dielectric constant upon storage at higher temperature as compared to the Tween 60-based creams. The creams containing Tween 60 showed a drastic rise in the dielectric constant with respect to temperature and showed signs of breaking after 28 days, which is in good agreement with conductivity observations. Viscosity. The result of changes in the viscosity of creams on exposure to various tem- peratures is presented in Figure 5. The viscosity of the creams ranged from 5600 to 6400 centipoises. The viscosity was found to decrease with the rise in storage temperature for all the creams tested. The viscosity of the cream prepared with polymer 2 was compar- atively less affected than the standard cream at all the temperatures. The fact that near constant viscosity could be achieved in a cream containing polymer 2 at various tem- peratures demonstrated that it maintains viscosity at elevated temperatures during long-term storage. The formulation containing Tween 60 showed signs of breaking after 28 days of storage at 55øC. The viscosity of these creams could not be determined because of this. B.8 e- o c) I].6 I].4 I].2 I ? 14 21 28 •õ 42 Time (Days) Figure 3. The changes in conductivity of the prepared creams during aging. RT: cream with Tween 60. R2: cream with polymer 2.