New alkyl N,N-dialkyl-substituted amino acetates as transdermal penetration enhancers

New alcohol derivatives of N,N-disubstituted amino acids with a low toxicity have been synthesized and evaluated for their transdermal penetration enhancing effects on the transport of indomethacin from petrolatum ointments across shed skin of black rat snake (Elaphe obsoleta). The derivatives show excellent penetration enhancement of indomethacin, as high as 3.8 times that of Azone, with decyl N,N-dimethylamino acetate as the lead compound in the series. The release of indomethacin from an ointment containing 1% indomethacin, 5% dodecyl N,N-dimethylamino acetate, and 94% petrolatum was 3.15 micrograms/min1/2/cm2. Saturation studies performed by incorporating varying concentrations of indomethacin, from 0.1 to 10%, into the ointments and determination of the fluxes of indomethacin demonstrated that the saturated concentration of indomethacin in petrolatum base was approximately 1%. Penetration fluxes of indomethacin (1%) through snake skin increased linearly as the concentration of dodecyl N,N-dimethylamino acetate increased from 2.5 to 15%. Experiments involving the pretreatment of the snake skins with dodecyl N,N-dimethylamino acetate indicated that pretreatment of the skin increased the skin permeability significantly. Electron micrograph studies on the snake skin treated with dodecyl N,N-dimethylamino acetate show clearly that the enhancer interacted with both the lipid-rich layer (mesos phase) and the keratin-rich layers (both alpha and beta phases).