Desenvolvimento de método de análise e estudo de estabilidade do ácido kójico associado ou não ao ácido glicólico em formulações tópicas / Development of analytical methods and the stability study of kojic acid associated or not glycolic acid in topics formulations

RESUMO

O desenvolvimento de métodos analíticos e o estudo de estabilidade de formulações cosméticas e farmacêuticas fazem parte do processo de garantia de qualidade, o qual tem por objetivo assegurar a eficácia e segurança no uso de tais produtos pelo consumidor. O ácido kójico é um agente despigmentante que pode estar associado ao ácido glicólico, um agente esfoliante, a fim de ter sua ação potencializada. O objetivo do presente trabalho foi o desenvolvimnto de um método analítico para a determinação do ácido kójico a 1 porcento associado ou não ao ácido glicólico a 5 por cento em formulações tópicas na forma creme e gel, a base de excipientes comumente utilizados em farmácias de manipulação, e a realização de um estudo acelereado para avaliar a estabilidade das mesmas...

ABSTRACT

The development of analytical methods and the stability study of cosmetics and pharmaceuticals are part of the quality assurance, which has for objective to guarantee the effectiveness and security in the use of such products for the consumer. Kojic acid is a depigmentant agent that can be used in association with glycolic acid, an exfoliant agent, in order to have its action maximized. The aim of this work was the development of an analytical method to assay kojic acid 1% associated or not with 5% glycolic acid in cream and gel form, based on excipients normally used in compounding formulations, and carried out an accelerated study to evaluate its stability. To determine kojic acid in such formulations it was employed an UV first-derivative spectrophotometric method (UVD), with "zero crossing" set in 256,8 nm, where the excipients interference could be annulled. To assay both acids in association it was validated a reversed phase HPLC method with ion pairing, employed a Synergi Hidro® C18 column, mobile phase NH4H2PO4/H3PO4 buffer 30 mmol -1 pH 3,0 plus TBA (tetrabutylammonium bromide) 2 mM : acetonitrila (95:5), flow rate of 0,7 mL/min and detector PDA set in 220 nm. The samples were easily extracted and the run time was 12 min. The same experimental conditions were used to the development of a HPLC method in order to determine the kojic acid isolated in cream and gel formulations. The UVD e HPLC methods were not statistically different in terms of accuracy and precision (p = 95%). The samples submitted to the accelerated stability study, for 90 days, were stored at 40±2ºC and light 25±2ºC. All samples were also stored at room temperature protected from light. Appearance, pH, rheology and amount of kojic and glycolic acids (by HPLC) were evaluated. At the end of the study, all the samples showed physical stability, but presented decline in kojic acid above 5% at 40±2ºC. Samples stored at not accelerated conditions preserved 90% of kojic acid concentration. Therefore, a 90 days expiration date may be considered for formulations with similar composition and packing, when stored at room temperature and protected from light.