Nanoemulsion–laden organogels of lidocaine as lipid–based systems for topical delivery

Conventional organogel and nanoemulsion–laden organogels (nanoemulsion organogels) were used to deliver the lipophilic drug, lidocaine, topically. Optimized formulations of lidocaine–loaded nanoemulsions of oil, water, and different ratios of surfactant to cosurfactant (Tween® 20: ethanol; 4:1 and 2:1 v/v) were selected based on the droplet size and physical stability of nanoemulsions. Nanoemulsions were then loaded into organogels. Lidocaine conventional organogel was prepared without the addition of nanoemulsion and was used as a reference. The rheological properties and release profiles of lidocaine organogels were investigated using a controlled-stress rheometer. The cumulative amount of lidocaine permeated through a synthetic membrane (Strat® M) and human excised SC was investigated using six vertical diffusion cells. Lidocaine organogels exhibited viscoelastic properties with more elastic behavior. Lidocaine conventional organogel exhibited the highest viscoelastic properties and lowest rate of release. Whereas, nanoemulsion organogel containing Tween® 20: ethanol (4:1 v/v) exhibited lower viscoelastic properties and a higher rate of release than those of nanoemulsion organogel containing Tween® 20: ethanol (2:1 v/v). Type and composition of organogels dictated the viscoelastic properties and rate of lidocaine release. The results obtained shed light on understanding the viscoelastic properties of organogel systems; as these mechanical factors play an important role in predicting the release behavior of drugs from these systems and their potential to enhance penetration of drugs through the skin.
Audience take away:
• Organogels and nanoemulsion have been used separately as topical drug delivery systems. 
• Both delivery systems can enhance the penetration of hydrophobic drugs.
• The loading of nanoemulsion into organogel has shown synergistic delivery effect topically. 
• The viscoelastic properties and in vitro and ex vivo release of organogels were type- and component-dependent.