[Lotion with hydroquione - tretinoin]

The observed precipitation in a lotion containing 4% of hydrochinon and 0,03% of tretinoine is evaluated. To dissolve both actives, 10% propyleneglycol is used and the alcohol concentration varied. From the results it is demonstrated that at least 54 ml of ethanol 96 degrees is necessary to dissolve both actives. It is also demonstrated that the addition of 0.2% of vitamin C, as antioxidant, is necessary to avoid coloration of the lotion, as a function of time, due to the presence of hydrochinon.