Triptolide-loaded microemulsion-based hydrogels: physical properties and percutaneous permeability

Triptolide is a diterpenoid compound that inhibits the inflammation of rheumatoid arthritis (RA). However, the use of triptolide is limited due to its strong gastrointestinal toxicity. The purpose of this work was to develop a transdermal delivery system for triptolide to reduce this toxicity. A microemulsion-based hydrogel (MBH) was prepared from the combination of Gemseal 40-oleic acid as oil phase, Tween 80-labrasol as surfactant, anhydrous ethanol as co-surfactant, water as aqueous phase and Poloxamer 407 as hydrogel matrix. Rheological measurements, environmental scanning electron microscopy (ESEM) and transdermal experiments in vitro were used to characterize triptolide-loaded and blank MBH preparations. The effects of Poloxamer 407 and triptolide on the rheological properties and microstructures of the MBH were determined. Transparent and homogeneous MBH could only be formed when the concentration of Poloxamer 407 in the selected O/W microemulsion was in the range of 14.0–16.0% ( w / w ). When the concentration of Poloxamer 407 increased, the rheological properties such as the yield stresses ( σ y ), storage and loss moduli ( G ′, G ″) of the formulations increased, and the network structures became more compact. The addition of triptolide did not change the interconnected network structures of the MBH preparations. MBH preparations afford a better sustained release profile when compared to microemulsions, a finding confirmed by an in vitro permeation test in mice. MBH appears to be a promising vehicle for transdermal delivery of triptolide.