Development and characterization of skin permeation retardants and enhancers: a comparative study of levothyroxine-loaded PNIPAM, PLA, PLGA and EC microparticles.

Polymeric microparticles suitable for topical and transdermal delivery systems were studied using poly D,L lactide (PLA), poly D,L lactide co glycoside (PLGA), poly (N-isopropylacrylamide) (PNIPAM) and ethyl cellulose (EC). Drug encapsulation efficacy, microparticle stability and skin permeation studies of levothyroxine loaded microparticles were carried out using excised human skin, and the skin permeation pattern was observed using confocal laser scanning microscopy. It was found that ethyl cellulose microparticles had the highest drug encapsulation and minimal drug leakage during the 14 week storage period.