pilocarpin

Pilocarpine is a naturally occurring alkaloid derived from the leaves of Pilocarpus species, most notably Pilocarpus microphyllus. It is a direct-acting muscarinic receptor agonist used in medicine to stimulate the parasympathetic nervous system. Pilocarpine is relatively resistant to hydrolysis by acetylcholinesterase, contributing to its sustained activity compared with acetylcholine.

Pharmacology and mechanism of action

Pilocarpine binds to muscarinic receptors, with clinical emphasis on the M3 subtype. Activation of these receptors increases glandular secretions and causes pupil constriction (miosis) and accommodation of the ocular outflow pathways. In the eye, this raises aqueous humor drainage through the trabecular meshwork and can reduce intraocular pressure. Systemically, pilocarpine enhances salivary and lacrimal secretions.

Medical uses

In ophthalmology, pilocarpine is used to induce miosis and to lower intraocular pressure in glaucoma and certain ocular emergencies. It can be employed to facilitate drainage in angle-closure situations and to prepare the eye for procedures. Systemically, pilocarpine is used to treat xerostomia (dry mouth) and symptoms of Sjögren’s syndrome by stimulating salivary and lacrimal glands.

Administration and pharmacokinetics

Pilocarpine is available as an ophthalmic solution (commonly 0.5% to 2%) and in oral tablet form. Ophthalmic administration provides rapid local effect with onset in minutes and duration of several hours. Oral or systemic administration yields broader cholinergic effects with a longer duration.

Safety and contraindications

Common adverse effects reflect cholinergic stimulation and include sweating, increased salivation, lacrimation, abdominal cramps, diarrhea, and bronchospasm. It can worsen bronchial conditions such as asthma and COPD and may aggravate peptic ulcers. Caution is advised in pregnancy and in patients with hypersensitivity to pilocarpine.