Concentration-dependent precorneal loss of pilocarpine in rabbit eyes.

Precorneal loss of pilocarpine was studied in pigmented and albino rabbits. We instilled 25 microliter of isotonic pilocarpine solution, pH 6.4, into rabbit eyes and monitored drug concentration in the precorneal tear film. Increased concentration (0.2% - 2.0%) of pilocarpine accelerated precorneal drug loss from the tear film from 0.686 min-1 to 1.064 min-1. This increase was mainly due to induced lacrimation. Polyvinyl alcohol (1.4%) retarded precorneal loss of pilocarpine. The rate of loss was the same in pigmented and albino rabbits. The effects of the changed precorneal loss of pilocarpine on corneal drug absorption are discussed.