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Twelve urea and thiourea compounds were examined for their transdermal penetration enhancing properties in vitro using hairless mouse skin and hydrocortisone as a model drug. Skins were pretreated for 1 h with the enhancer in propylene glycol before application of the drug also in propylene glycol. Enhancement ratios ( ER ) were calculated for permeability coefficient ( P ), 24 h receptor concentration ( Q 24 ), and skin content of drug ( SC ) and compared to control values (no enhancer present). Control values for permeability coefficients were 0.71±0.27 cm h −1 , 24 h receptor concentration: 11.9±3.4 μ M, and skin content of drug 44.6±18.5 μ g g −1 . The most effective enhancer of the series was 1-dodecyl-3-methylthiourea. This enhancer produced the highest values for all three penetration parameters with a permeability coefficient 4.7±1.8×10 −4 cm h −1 ( ER P 6.6), a 24 h receptor concentration of 62.7±16.3 μ M ( ER Q 24 5.3), and a skin content of 90.1±17.7 μ g g −1 ( ER SC 2.0). A structure-activity relationship was observed in that the thio-substituted analogs were more effective enhancers than the oxygen-containing compounds. Although these compounds show promise as penetration enhancers, further study is needed to determine their effectiveness with other drugs and their irritation potential. |
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