title: New vehicle based on a microemulsion for topical ocular administration of dexamethasone.
abstract: OBJECTIVE
  Eye drops are the most used dosage form by the ocular route, in spite of their low bioavailability. Due to their properties and numerous advantages, microemulsions are promising systems for topical ocular drug delivery. They can increase water solubility of the drug and enhance drug absorption into the eye. The present study describes the development and characterization of an oil-in-water microemulsion containing dexamethasone and the evaluation of its pharmacokinetics in rabbits after topical ocular application.
  
  
  METHODS
  The microemulsion was prepared by the titration technique. Its physico-chemical characteristics and stability were determined. The ocular irritation test and the pharmacokinetics of this system were studied in white rabbits.
  
  
  RESULTS
  The developed system showed an acceptable physico-chemical behaviour and presented good stability for 3 months. The ocular irritation test used suggested that the microemulsion did not provide significant alteration to eyelids, conjunctiva, cornea and iris. This formulation showed greater penetration of dexamethasone in the anterior segment of the eye and also release of the drug for a longer time when compared with a conventional preparation. The area under the curve obtained for the microemulsion system was more than twofold higher than that of the conventional preparation (P < 0.05).
  
  
  CONCLUSIONS
  The microemulsion-based dexamethasone eye drop is advantageous for ophthalmic use because it is well-tolerated in the eye and seemed to provide a higher degree of bioavailability. The developed system shows greater penetration in the eye, allowing the possibility of decreasing the number of applications of eye drops per day.
authors.affiliation: Laboratory of Pharmaceutical Technology, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Sílvia Ligório
authors.initials: SL
authors.lastname: Fialho
authors.forename: Armando
authors.initials: A
authors.lastname: da Silva-Cunha
mesh_terms: D000287:Administration, Topical; D000818:Animals; D000869:Anterior Eye Segment / Q000378:metabolism; D019540:Area Under Curve; D001548:Benzalkonium Compounds / Q000737:chemistry; D001682:Biological Availability; D003907:Dexamethasone / Q000008:administration & dosage* / Q000493:pharmacokinetics; D016503:Drug Delivery Systems; D004655:Emulsions; D005938:Glucocorticoids / Q000008:administration & dosage* / Q000493:pharmacokinetics; D006863:Hydrogen-Ion Concentration; D009226:Myristates / Q000737:chemistry; D009883:Ophthalmic Solutions; D004364:Pharmaceutical Preparations; D019946:Propylene Glycol / Q000737:chemistry; D011817:Rabbits; D014783:Viscosity
chemical_list: D001548:Benzalkonium Compounds; D004655:Emulsions; D005938:Glucocorticoids; D009226:Myristates; D009883:Ophthalmic Solutions; D004364:Pharmaceutical Preparations; C008205:isopropyl myristate; D019946:Propylene Glycol; D003907:Dexamethasone