The secondary lichen metabolite usnic acid [2,6-diacetyl-7,9-dihydroxy-8,9b-dimethyl-1,3(2H,9bH)-dibenzofuran] has demonstrated pharmacological potential activities such as antitumor, antimicrobial, antiviral, antiproliferative, and anti-inflammatory. Liposomes are vesicles composed of phospholipid bilayers surrounding aqueous compartments and they have been used as colloidal drug carriers. The aim of this study was to develop and validate a quantitative UV spectrophotometric method for determination of usnic acid in liposomal formulations. The validation parameters were assessed according to The International Conference on Harmonization (ICH) and American Pharmacopoeia guidelines. The linearity range was of 3-15 µg.mL-1, regression equation: absorbance = 0.070 x UA concentration (µg.mL-1) + 0.013, and r = 0.9997. The repeatability (relative standard deviation) of the method was 1.96% and intermediate precision indicated that the difference among mean was statistically insignificant (P < 0.05). The accuracy revealed a mean percentage recovery of 100.4% of usnic acid. The method was robust for the variation of temperature and solvent. The detection and quantization limits were found to be 0.34 and 1.13 µg.mL-1, respectively. The content of usnic acid in liposomes was of 96.8% (± 0.2). The proposed method is accurate, precise and reproducible for estimation of usnic acid as raw material and in pharmaceutical dosage forms such as liposomes.
Usnic acid; Liposomes; Ultraviolet Spectrophotometry; Quantitative analysis
