title: Development and characterization of skin permeation retardants and enhancers: a comparative study of levothyroxine-loaded PNIPAM, PLA, PLGA and EC microparticles.
abstract: 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. The PNIPAM microparticles had the lowest drug encapsulation efficiency and a fast degradation rate. The PLGA microparticles exhibited a temperature dependent drug leakage. Permeation studies using a flow-through diffusion cell indicated that the polymer transition temperature (T(g)) may influence the skin permeation rate of levothyroxine. Polyesters (PLA and PLGA) and PNIPAM acted as a skin penetration retardant and caused skin accumulation of the drug. These microparticles have potential use in skin formulations containing sunscreens and other active ingredients that are meant to be concentrated on the skin surface. However, skin permeation was observed from EC microparticles, therefore such polymers may be used as carriers in transdermal formulations to help achieve therapeutic concentrations of the drug in the plasma.
authors.affiliation: Department of Pharmacy, National University of Singapore, Block S4, Level 2, Science Drive 4, 117543 Singapore.
authors.forename: Anahita Fathi
authors.initials: AF
authors.lastname: Azarbayjani
authors.forename: Jia Vu
authors.initials: JV
authors.lastname: Khu
authors.forename: Yew Weng
authors.initials: YW
authors.lastname: Chan
authors.forename: Sui Yung
authors.initials: SY
authors.lastname: Chan
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry* / Q000378:metabolism; D002482:Cellulose / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D004337:Drug Carriers; D004355:Drug Stability; D004356:Drug Storage; D006801:Humans; D019344:Lactic Acid / Q000737:chemistry* / Q000378:metabolism; D018613:Microscopy, Confocal; D008855:Microscopy, Electron, Scanning; D010316:Particle Size; D010539:Permeability; D011091:Polyesters; D011100:Polyglycolic Acid / Q000737:chemistry* / Q000378:metabolism; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry* / Q000378:metabolism; D012867:Skin / Q000737:chemistry*; D013974:Thyroxine / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000180:Acrylic Resins; D004337:Drug Carriers; D011091:Polyesters; D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; C052970:poly-N-isopropylacrylamide; D011100:Polyglycolic Acid; D019344:Lactic Acid; C033616:poly(lactide); C013517:ethyl cellulose; D002482:Cellulose; D013974:Thyroxine