Formulation of microemulsion gel systems for transdermal delivery of celecoxib: In vitro permeation, anti-inflammatory activity and skin irritation tests.

The aim of this study was to develop suitable microemulsion gel systems for transdermal delivery that could assist dissolution enhancement of poorly water soluble celecoxib and thus improve its skin permeability. Long term oral administration of celecoxib causes serious gastrointestinal adverse effects, which makes it a good candidate for transdermal formulations, yet its low water solubility (4 mg/L) makes this challenging. Ternary phase diagrams were constructed using isopropyl myristate and oleic acid as oils, Tween 80 as surfactant, and Cremophor RH40 as cosurfactant. Microemulsion areas were identified and two systems each of 36 formulas were prepared and assessed for visual inspection, spreadability, pH measurements, and droplet size analysis. Drug release and in vitro permeation of celecoxib from microemulsion formulas through semi-permeable membranes and excised abdominal rabbit skin, respectively, were carried out and compared to celecoxib cream. In all tested formulas, celecoxib was released and permeation was at a higher rate than that from the corresponding cream. The optimized formula (F12) was found to be superior to all other formulas. This formula increased the permeation rate of celecoxib up to 11 times compared to that of the cream. Its stability was retained after one year of storage under ambient conditions and its anti-inflammatory effect was significantly higher than that of celecoxib cream and the oral commercial formula. Skin irritancy and histopathological investigation of rat skin revealed its safety. The results revealed that the developed microemulsion gel has great potential for transdermal delivery of celecoxib.