Fig. 8

Plot of log(PS/mL g⁻¹ min⁻¹), versus log(K_{n-octanol/water} MW^−1/2) for the substances indicated along the abscissa. PS is the product of permeability and surface area for the blood–brain barrier, K_{n-octanol/water} is the octanol/water partition coefficient and MW is the molecular weight of the substance. The slope of 1 for the heavy blue line indicates PS proportional to K_{n-octanol/water} MW^−1/2. A closer fit to the data can be obtained by allowing the slope to vary, shown as the thin red line, but the improvement in fit is not statistically significant (F = 2.33, p = 0.11, n = 43, extra sum of squares F test [640])