Rapid and simultaneous determination of dexamethasone and dexamethasone sodium phosphate using HPLC-UV: Application in microneedle-assisted skin permeation and deposition studies.

Dexamethasone is a fluorinated derivative of the natural glucocorticoid, cortisone, with a very high systemic anti-inflammatory effect. In this study, a simple and rapid high performance liquid chromatography (HPLC) method was developed and validated to quantify dexamethasone and its prodrug dexamethasone sodium phosphate in skin permeation studies. The separation of both the compounds was achieved on a Vydac Denali C column(250 × 4.6 mm, 5 μm) with a mobile phase composed of 5 mM ammonium acetate buffer-acetonitrile-methanol (43:32:25, v/v) at a flow rate of 0.9 mL/min and UV detection at 240 nm. The standard curves were found to be linear in the range from 0.5 to 100 µg/mL for both the drugs and the method could successfully separate the drug peaks from interfering peaks of endogenous skin constituents. Accuracy values of both the drugs were within 98.60 to 108.60% (intra-day) and 98.70 to 107.20% (inter-day) and precision values were within 2% at the studied concentrations. The developed method was used to investigate the effect of microneedles on transdermal delivery of dexamethasone sodium phosphate. The hydrolysis of dexamethasone sodium phosphate to dexamethasone in the presence of rat skin homogenate and rat plasma was also evaluated to confirm the conversion that occurs during skin permeation and in the blood circulation. The skin permeation and deposition characteristics of microneedle-assisted diffusion were compared to those achieved by passive diffusion. The observed data demonstrated that transdermal permeation of dexamethasone is significantly enhanced with microneedle pretreatment of rat skin, showing a marked increase in flux and permeability coefficient, compared to passive diffusion. This simple isocratic HPLC method can, be effectively applied for the evaluation of skin permeation of topical/transdermal dexamethasone formulations.