Studies On Hydroquinone Gels

Hydroquinone (HQ) was used for the gradual bleaching of hyper-pigmentation skin conditions such as chloasma, melasman, freckles, senile lentigines, and other unwanted areas of melanin hyperpigmentation in clinics. The solution of HQ was very unstability. Air, light and metal ion had great effect on physical-chemical stability of HQ. And thus, the HQ gels were developed.Firstly basic physical-chemical properties of HQ were investigated. The results showed that HQ belonged to hydrophilic drug and was a poor membrane permeation agent. The effects of pH on the solubility of HQ were studied. It was shown that it had no significant difference, but the solubility of pH 2 and 8.5 is higher than other pH in the studies. Horizontal and vertical diffusion cell was used to evaluated the permeability of HQ gels by the skin of rat. The result showed that the permeability was poor. It is available to the treatment of hyperpigmentation.The emulsifier in water method was established to prepare HQ emulsion and then the HQ gels were prepared using carbopol as matrix. Optimal formulation was acquired by orthogonal experiment with BHT of 1%, tween-80 of 7%, NaHSO3 of 1.5% and EDTA of 0.02%,carbopol 2%. The HQ gels of optimal formulation was white with homogeneous diameter, pH 5.5-6.5 and stable. A reversed phase HPLC method was established for the determination of concentration of HQ.All the preparations were stable during the stability study. It was notfound in the test of creaming flocculation, coalescence and breaking. The result of rabbit-skin irritation test showed that the HQ recipes had no irritation. These gels fit the requirement on gels regulated by Chinese Pharmacopoeia.The HQ gels were found to have the inhibition effect on the activity of tyrosinase in vitro. Tyrosinase is the key enzyme in production procedure of melanin. The quantity of melanin can be controlled by restricting the activity of tyrosinase. With the increasing of the concentration of HQ, the rate of inhibiting is up.