Poloxamer 188

The in-vitro skin permeation of RT from the NEG systems was evaluated using a static Franz diffusion cell [24 (link)]. A Franz diffusion cell is divided into two compartments (donor and receptor compartments) and a sample of shaved, excised dorsal skin from Wistar rats was mounted between these two compartments. The RT-NEG sample was applied to the donor compartment, while the receptor compartment was filled with release medium (PBS, pH 5.5) and the whole assembly was maintained at 37 °C. Aliquots were collected at different time intervals (0, 0.25, 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 h) and replaced by an equal volume of receptor media. The aliquots were analyzed using a UV spectrophotometer (λmax 325 nm) to elucidate the cumulative amount of drug that had permeated the skin by the various time intervals.
In-vitro drug deposition within the skin was evaluated using the same skin samples utilizing the tape-stripping technique [25 (link)]. The skin samples were unclipped from the Franz diffusion cells after 24 h of the permeation study and then washed with PBS. Cellophane tape was used for the tape stripping of skin. The first strip of tape was discarded due to the fact they potentially contained drug that was adhered to the surface of the skin sample. Approximately 10 strips were used in the removal of the entire subcutaneous (SC) layer of skin, in a manner that utilized the maximum area of tape. The treated skin samples and tape used for the stripping procedure were both then chopped and incubated in ethanol to completely extract the RT. Afterward, samples were sonicated for 15 min and then centrifuged at 3000 rpm for 15 min. The extracted samples were analyzed by UV spectroscopy at λmax 325 nm to measure the amount of RT deposited in the skin. This procedure for quantifying the skin permeation was then repeated for the RT-gel (accurately weighed amounts of RT dissolved in the small quantity of propylene glycol and dispersed into placebo gel to obtain RT-gel of strength 1% w/w) and RT creams (accurately weighed amounts of RT in the required quantity of cream base [composed of PEG 4000, PEG 400, lanolin, glyceryl monostearate, and poloxamer 188] to obtain a RT cream at a concentration of 1% w/w) in order to compare the skin permeation of RT with that of the developed NEG systems.