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1617078 
Journal Article 
Hydrogel-thickened microemulsion for topical administration of drug molecule at an extremely low concentration 
Chen, H; Mou, D; Du, D; Chang, X; Zhu, D; Liu, J; Xu, H; Yang, X 
2007 
Yes 
International Journal of Pharmaceutics
ISSN: 0378-5173
EISSN: 1873-3476 
341 
1-2 
78-84 
English 
17570625 
WOS:000249138300009 
In this work, a hydrogel-thickened microemulsion (HTM) was investigated for delivering an extremely low concentration of drug molecule. The pseudo-ternary phase diagrams were constructed using isopropyl myristate (IPM), Tween 80, propylene glycol and water. The various HTM were prepared and characterized. We described that HTM has the combination of o/w microstructure of microemulsion and the three-dimensional gel network of hydrogel in continuous phase using transmission electron microscope. The stability tests showed that HTM had good stability. The influence of the addition of hydrogel into microemulsions on the viscosity and permeation ability is investigated. The abilities of HTM to deliver an extremely low concentration of triptolide as a model drug were evaluated using the in vitro permeation studies. The permeation rates of triptolide from various HTM were 2.2-3.6 times over that from the control hydrogel. The addition of 2% menthol into HTM consisting of 3% IPM, 30% Tween 80, 15% propylene glycol, 0.75% carbomer 940 resulted in the highest permeation rate of 0.105+/-0.006microcm(-2)h(-1), which was 5.8 times over control gel. The powerful permeation enhancing ability of HTM with a suitable viscosity makes it promising alternative carrier for transdermal administration of drug molecule at an extremely low concentration. 
microemulsion; hydrogel; transdermal delivery; triptolide