Systemic use: Pilocarpine is primarily metabolized by CYP2A6 and has demonstrated a capacity to inhibit CYP2A6 in vitro. Serum esterases are also involved in the biotransformation of pilocarpine to pilocarpic acid. Approximately 35% of dose is eliminated as 3-hydroxypilocarpine in urine and 20% of dose is excreted unchanged in the urine. Mean elimination half-lives for pilocarpine is 0.76 and 1.35 hours after repeated oral doses of 5 and 10 mg of pilocarpine hydrochloride, respectively.
Salagen® (Pilocarpine) 5mg Film Coated Tablets UK Summary of Product Characteristics, Novartis Pharmaceuticals UK Ltd, updated November 2011

Ocular use: Systemic reactions rarely occur when treating chronic simple glaucoma at normal doses. However, in the treatment of acute closed-angle glaucoma the possibility of systemic reactions must be considered because of the higher doses given. Pilocarpine has a low ocular bioavailability when topically applied and this has been attributed to extensive pre-corneal drug loss in conjunction with the resistance to normal corneal penetration. Further, pilocarpine appears to bind to the eye pigments from which it is gradually released to the muscles. Inactivation of pilocarpine in the eye is thought to occur by a hydrolysing enzyme. The amount of this enzyme is not changed by the prolonged use of pilocarpine by glaucoma patients, nor is it changed in patients poorly controlled by glaucoma therapy.
Minims Pilocarpine Nitrate 2% w/v Eye drops solution UK Summary of Product Characteristics, Bausch & Lomb U.K Limited, updated July 2012