title: Viscoelastic properties of Carbopol 940 gels and their relationships to piroxicam diffusion coefficients in gel bases.
abstract: OBJECTIVE
  This study was conducted to determine the effect of formula compositions on viscoelastic properties of piroxicam gels using Carbopol 940 as a gelling agent and to determine the relationships between viscoelastic properties of Carbopol 940 gel bases and diffusion coefficients of piroxicam in gel bases.
  
  
  METHODS
  Piroxicam gels (1.0% w/w) were prepared by using Carbopol 940 as a gelling agent and varying Carbopol 940 concentrations, glycerin, and sodium chloride contents. The in vitro release of piroxicam from gel bases to the receiving media, isotonic phosphate buffer solution (pH 7.4), were carried out using Franz-modified cell. The piroxicam diffusion coefficients were obtained by Higuchi's equation. Rheological property measurements of gel samples were performed via a cone and plate fluid rheometer. Relationships between viscoelastic properties of gel samples and piroxicam diffusion in gel bases were analyzed by Pearson's test at a p value of less than 0.05.
  
  
  RESULTS
  All piroxicam gels exhibited predominantly elastic solid behavior whose magnitude depended on Carbopol 940 concentration. Preparations containing good solvent exhibited more elastic solid characters. In contrast, the piroxicam gels containing higher sodium chloride contents possessed more viscous fluid behavior. Analyzed by Pearson's test at a p value of less than 0.05, piroxicam diffusion coefficients were directly proportional to loss tangent, but were inversely proportional to storage modulus, loss modulus, complex modulus, and viscosity.
  
  
  CONCLUSIONS
  There is a potential for predicting drug diffusion coefficients from their correlations to rheological parameters. This could be beneficial to the formulation design of transdermal drug delivery systems including mucoadhesive drug delivery systems.
authors.affiliation: Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok, Thailand. rathapona@hotmail.com
authors.forename: Rathapon
authors.initials: R
authors.lastname: A-sasutjarit
authors.forename: Anuvat
authors.initials: A
authors.lastname: Sirivat
authors.forename: Panida
authors.initials: P
authors.lastname: Vayumhasuwan
mesh_terms: D000180:Acrylic Resins / Q000737:chemistry*; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000008:administration & dosage / Q000737:chemistry*; D002626:Chemistry, Pharmaceutical; D004058:Diffusion; D004356:Drug Storage; D004548:Elasticity; D004573:Electrolytes; D005782:Gels; D008567:Membranes, Artificial; D010894:Piroxicam / Q000008:administration & dosage / Q000737:chemistry*; D012212:Rheology; D012997:Solvents; D014783:Viscosity
chemical_list: D000180:Acrylic Resins; D000894:Anti-Inflammatory Agents, Non-Steroidal; D004573:Electrolytes; D005782:Gels; D008567:Membranes, Artificial; D012997:Solvents; D010894:Piroxicam; C006903:carbopol 940