The relations between ionic and non-ionic diffusion of sulfonamides across the rabbit cornea.

We studied the transcorneal permeability of five carbonic anhydrase inhibitors, with particular attention to the passage of these acidic compounds in their ionized and nonionized forms. Their pKs varied from 5.9 to 8.0, and CHCl3/pH 7.2 buffer partition coefficients from 10(-4) to 25. Solutions of appropriate pH of each compound were applied to the cornea in steady state, and the rates of passage to the anterior chamber for each compound in each form were measured. The rate constants for the ionized forms were surprisingly high, only four- to sevenfold less than those for the uncharged species. Thus these compounds penetrate the cornea in both forms, and the data show that by increasing the pH of solutions, and thereby solubility, the overall rates of accumulation in the eye are increased.