Spectrophotometric method to quantify tofacitinib in lyotropic liquid crystalline nanoparticles and skin layers: Application in ex vivo dermal distribution studies.

Tofacitinib is an oral Janus kinase inhibitor used in the treatment of Rheumatoid arthritis. The topical delivery of novel Tofacitinib loaded liquid crystal nanoparticles (LCNPs) can provide a controlled release, and also targeted drug delivery to inflamed synovium. There is need of UV spectroscopic method which can determine Tofacitinib in designed nanocarriers like LCNPs, that can be applied to evaluate entrapment efficiency, in vitro drug release, and ex vivo skin studies. In the present study, we have developed and validated a simple and sensitive spectrophotometric method for the quantitative determination of Tofacitinib in methanol and phosphate buffer saline. The linearity range in both the media was 5-30 µg/mL (methanol) and 5-40 µg/ mL (phosphate buffer saline) with high correlation coefficient value (>0.9998). This indicates the clear correlation between Tofacitinib concentrations and their absorbance within the test ranges. The repeatability and intermediate precision articulated by the relative standard deviation were less than 2% in the developed method. The method specificity and applicability were also ascertained by performing recovery studies by spiking method, which was 95.85 ± 1.98% with % RSD 1.24 ± 0.045. The method developed in methanol was successfully applied to determine the entrapment efficiency of Tofacitinib in developed LCNPs formulation and skin retention (dermatokinetics). The method developed in pH 7.4 phosphate buffer saline was applied to quantify Tofacitinib from LCNPs in in vitro and ex vivo drug release samples. In conclusion, a simple, sensitive, accurate, and precise UV spectrophotometric method was established to determine Tofacitinib in in vitro and ex vivo skin studies.