Level III, retrospective case control study.

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Background: Tretinoin is one of the commonly used medications in treatment of skin aging symptoms. However, its topical application leads to local irritation at the application site which often limits its tolerability by patients. Solid lipid nanoparticles (SLN) have been developed as an alternative carrier system to emulsions with several advantages such as possibility of controlled drug release, drug targeting and increased drug stability. Methods: In this study, we formulated SLN with hot high pressure homogenization technique. For all formulations the lipid phase was dispersed in water containing 1-3% nonionic surfactant at 75 0 C and a premix was formed by homogenizing in an IKA Ultra Turrax high-speed stirrer followed by an IKA high pressure homogenizer. We applied 3, 5, 7 and 9 cycles at pressure range of 250-1000 bars. The z-average and zeta potential was analyzed by Malvern Zetasizer ZEN 3600. Results: The property of the particles depends on the amount of surfactant, production pressure and the number of homogenization cycles. The best formulation which was stable for two years contained 10% cetyl palmitate as a lipid, 2% tego care 450 as a surfactant and 88% water at 1000 bars (5 cycles) with z-average of 140±5 nm. Conclusion: The in vitro release studies showed that SLN containing tretinoin has prolonged profile as compared to commercially available tretinoin creams. It appears that the prolong release profile sustains permeation and absorption of tretinoin and also provides skin tolerability.

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