HPLC-MS/MS method for the pharmacokinetics of homosalate after topical administration in rats

Homosalate is a UV filtering agent used in sunscreens and cosmetics for skin protection purposes. Despite the widespread use of these products, the extent of in vivo exposure to homosalate has not been elucidated. This study first reports the development of a rapid and sensitive high performance liquid chromatography-tanden mass spectrometry (HPLC-MS/MS) method for the analysis of homosalate in rat plasma and its pharmacokinetic characterization after topical application. Chromatographic separation was achieved using a Kinetex C ₁₈ column (50 mm × 2.1 mm, 2.6 m). The mobile phase was a mixture of acetonitrile and 0.05% formic acid (82.5:17.5 v/v). The multiple reaction monitoring was based on the transition of m/z 263.2 → 139.0 for homosalate and 251.2 → 139.0 for octyl salicylate (internal standard). The present method was found to be linear in the concentration range of 0.2-400 ng/mL (r > 0.999). The intra-and inter-day assay accuracy and precision ranged from 92.8 to 107.6% and 3.9 to 7.0%, respectively. The developed assay was successfully applied to a pharmacokinetic study in rats after topical application of gel containing homosalate (dose 1.8 mg). The maximum plasma concentration (7.9 ± 2.7 ng/mL) was achieved at 11.3 ± 1.6 hr, indicating a prolonged absorption of homosalate after topical application.