Topically applied pilocarpine. Human pupillary response as a function of drop size.

Previous studies with use of animal models have shown that, for topically applied ophthalmic drugs, the fraction of dose absorbed into the eye is increased as the volume in which the drug is instilled is decreased. Such findings have not previously been confirmed in humans. In the present study, the miotic response to instilled doses of 20 and 50 microL of 0.5% pilocarpine hydrochloride was compared in ten adult human volunteers. Although the 20-microL drop represents a substantial dosage reduction, the miotic response was essentially equivalent to that obtained with the 50-microL drop. These findings imply that, due to the large drainage loss of topically applied ophthalmic drugs, volumes delivered by commerical ophthalmic droppers may in some cases be larger than required to achieve the desired response.