Studies on rabbit corneal permeability of local anesthetics (I)

To elucidate the pharmacokinetics of local anesthetics with respect to corneal permeability in the rabbit, we examined the relationship between the corneal permeability velocities of three agents, cocaine X HCl, procaine X HCl and tetracaine X HCl and corneal hydration. The corneal permeability velocity constants (k) of these three ester-type local anesthetics were approximately 0.5-6.0 X 10(-6) cm/sec and the membrane permeability constants of these agents were approximately 0.5-4.0 X 10(-7) cm2/sec, whereas the rabbit corneal hydration values were 3.2-4.2. Tetracaine X HCl with the strongest topical anesthetic action showed the greatest corneal hydration and the smallest corneal permeability velocity constant among these local anesthetics. Rabbit corneal permeability decreased with increasing molecular length of the agents. Permeability of these local anesthetics in the rabbit cornea appears to result from passive transport. As corneal hydration values and the corneal permeability constant increased with greater topical anesthetic activity, it appears that the degree of inhibition of Na+-K+ ATPase activity is associated with the order of topical anesthetic activity in a similar manner as general anesthetics.