title: The effect of additives on release and in vitro skin retention of flavonoids from emulsion and gel semisolid formulations.
abstract: OBJECTIVE
  To assess the effect of two different additives (propylene glycol (PG) and polyethylene glycol 400 (PEG 400)) on release and in vitro skin retention of quercetin and chrysin from semisolid bases (amphiphilic creams and acidic carbomer gels).
  
  
  METHODS
  For obtaining semisolid formulations, flavonoids were pre-dissolved in the liquid (PG or PEG 400) or directly suspended in the semisolid base. Three chrysin formulations ('cream 0', 'PG-cream' and 'PEG 400-cream') and five quercetin formulations ('cream 0', 'PG cream', 'PEG 400 cream', 'gel 0' and 'PG gel') were prepared. The release studies were carried out in Franz diffusion cells by means of a cellulose membrane. The porcine ear skin was used in in vitro skin retention studies.
  
  
  RESULTS
  The dissolution was a prerequisite to increase the release rates of tested flavonoids from obtained semisolid formulations. The cumulative amount of chrysin released after 6 h from 'PEG 400 cream' containing partly dissolved form of that flavonoid was higher than that from 'cream 0' or 'PG cream' containing its suspended form. The formulations containing quercetin dissolved in PG ('PG cream', 'PG gel') or PEG 400 ('PEG 400 cream') exhibited higher release rates of that flavonoid than corresponding semisolid suspensions ('cream 0' or 'gel 0'). The effects of both liquid additives (PG and PEG 400) on the cumulative amount of quercetin released after 6 h were comparable. However, there was no correlation between the release rate and the skin retention. The amounts of the flavonoids found in the skin were strongly affected by the type of the used solvent. While PG increased the skin retention of both flavonoids, PEG 400 had no effect on chrysin skin retention and delayed quercetin skin absorption.
  
  
  CONCLUSIONS
  The proper choice of the solvent added to the semisolid base is crucial for enhanced skin delivery of the tested flavonoids. PG is more efficient absorption promoter than PEG 400 of both chrysin and quercetin.
authors.affiliation: Department of Pharmaceutical Technology, Medical University of Silesia in Katowice, Kasztanowa 3, Sosnowiec, 41-200, Poland.
authors.forename: R
authors.identifier: http://orcid.org/0000-0001-8980-7385
authors.initials: R
authors.lastname: Dyja
authors.affiliation: Institute of Cosmetology, University of Applied Sciences in Nysa, COLLEGIUM MEDICUM im. Konrada Emila Blocha, Ujejskiego 12, Nysa, 48-300, Poland.
authors.forename: A
authors.initials: A
authors.lastname: Jankowski
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D004655:Emulsions; D005419:Flavonoids / Q000008:administration & dosage* / Q000378:metabolism; D005782:Gels; D066298:In Vitro Techniques; D012867:Skin / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013552:Swine
chemical_list: D004655:Emulsions; D005419:Flavonoids; D005782:Gels
keywords: flavonoids; formulation skin care; penetration enhancer; skin barrier; skin delivery