Basic Pharmaceutical Research on Formulation of Kojic Acid Ointment for Hospitals-In vitro Releace Test and Evaluation of Permeability-.

An inhibitor of melanin synthesis, kojic acid (KA) is prescribed for the treatment of skin diseases such as chloasma in hospitals. To select the optimal formulation for achieving efficacy with KA, the relationship between KA release via a synthetic membrane filter and the permeability and penetration in rat skin were investigated. Further, the coefficient of friction of KA ointments was measured as an index of their spreading on the skin. Hydrophilic, white vaseline and macrogol ointments were prepared for this study. The KA content for all three ointments was 1%. Both studies were conducted with a Franz-type diffusion cell. For the in vitro permeability and penetration study, skin samples were taken from the abdominal region of male SD rats from which the hair had been removed. In the study in which KA release via a filter membrane was measured, the release rate for the hydrophilic and macrogol ointments was greater than for white vaseline. In the rat skin test, the hydrophilic ointment produced the highest KA level. Unexpectedly, the white vaseline ointment demonstrated the next highest penetration rate for KA. We therefore concluded that in addition to KA being directly transferred from the ointment, there may also be penetration of the KA within oily ointment bases. Another finding was that lanolin (added as a solubilizing agent), increased the coefficient of friction of the hydrophilic ointment. Overall, the hydrophilic KA ointment without lanolin was considered to be the best formulation among the ointments we prepared.