Method validation
The analytical methods were validated according to ICHQ2R1 (International Consensus on Harmonization, 2015) (18). Two calibration curves were developed: one using a mixture of acetonitrile, hexane and water for inyection (WFI) as diluent (for chemical stability of ointment, emulsion and gel formulations), and the other using methanol (for chemical stability of liposomes). The interday and intraday precision and accuracy of the methods was established using six concentration levels (0.025, 0.05, 0.075, 0.1, 0.125 and 0.15 mg/ml) in duplicate on three different days. The least squares method was used to evaluate linearity calculating a regression line between concentrations and peak areas of the chromatogram.