Skin absorption of solvent mixtures--effect of vehicles on skin absorption of toluene.

The skin absorption rates of toluene in various solvent mixtures were investigated in mice. The skin absorption rate of toluene in toluene/methanol mixtures exhibited a parabolic relationship to the mixed ratio. The maximum rate was obtained at a mixed ratio of 50% (V/V). The skin absorption rate of toluene at this point (50%) was about 4.7 times higher than that of pure toluene. The permeability coefficient (Kp) of toluene increased as the mixed ratio of methanol increased. Methanol enhanced skin absorption of toluene. The skin absorption rate of toluene in a toluene/benzene mixture was inversely proportional to the concentration of benzene. The Kp of toluene is kept constant through the mixed ratios of benzene, and benzene does not have an enhancing effect on the skin absorption of toluene contained in the toluene/benzene mixture. We examined the effects of various vehicles on the skin absorption rates of toluene in mixtures containing 50% (v/v) of toluene. Methanol was a good penetration enhancer for toluene, and its effect is similar to the effect of well-known skin penetration enhancers like DMSO, N,N-Dimethylacetamide, and N,N-Dimethylformamide. Therefore, it is necessary to take special precautions against the skin absorption of toluene when handing thinners that contain methanol.