Pharmacokinetics of topical phenylephrine hydrochloride in the normal human eye.

Solutions of phenylephrine hydrochloride at concentrations of 1, 2 and 5% were instilled in one eye of 5 normal volunteers. Both eyes were photographed concurrently with an infrared film, and the pupil diameter was determined by an image analyzer using the developed film. The mydriatic effects were expressed by the difference in the pupil diameter of the experimental and the fellow control eyes determined concurrently. The mydriatic effects with these 3 solutions reached a peak about one hour and 15 minutes after instillation; the peak effects and the logarithm of the drug concentrations showed a linear relationship. An extrapolation of the relationship gave a least effective concentration of 0.07%. From the time course of the mydriatic effects, the pharmacokinetic coefficients were calculated using a computer. The average values were 0.24 +/- 0.08 hour for the time lag of the mydriatic response to appear, 1.31 +/- 0.19 hour-1 for the apparent elimination rate constant and 1.47 +/- 0.28 hour-1 for the apparent absorption rate constant.