Pilocarpine was first isolated in 1875 from the leaves of the South American plant Pilocarpus jaborandi, and it soon entered medical use in the late 19th century due to its strong parasympathomimetic effects. It is a muscarinic receptor agonist that stimulates the parasympathetic nervous system, leading to increased secretion of sweat, saliva, and tears, as well as contraction of smooth muscles such as the ciliary muscle in the eye. Clinically, pilocarpine is most commonly used to treat glaucoma by lowering intraocular pressure through improved aqueous humor outflow, and it is also used to manage dry mouth (xerostomia), especially in conditions like Sjögren’s syndrome or after head and neck radiation therapy. Its long history in medicine reflects its continued value in ophthalmology and supportive care despite the development of newer agents.
BRAND NAMES
Salagen – oral tablets used mainly for dry mouth (xerostomia)
Isopto Carpine – ophthalmic (eye drop) form used for glaucoma
Pilocar – eye drop formulation used in some regions
Pilocarpine Hydrochloride – often used as a generic label but also appears as a branded ophthalmic product in certain markets
Pilopine hs
Ocusert pilo-20
Ocusert pilo-40
Qlosi
Vuity
MECHANISM OF ACTION
Pilocarpine is a direct-acting muscarinic receptor agonist that stimulates the parasympathetic nervous system. In the eye, it causes contraction of the ciliary muscle and constriction of the pupil, which increases aqueous humor outflow and lowers intraocular pressure in glaucoma. It also stimulates secretions from salivary and sweat glands, making it useful in treating dry mouth conditions.
PHARMACOKINETICS
Absorption
Pilocarpine is well absorbed after oral administration, with peak plasma levels typically reached within about 1 hour. When used as ophthalmic drops, it is also absorbed through the cornea, but systemic absorption is lower compared to oral use.
Distribution
Pilocarpine is widely distributed throughout body tissues after absorption. Because it is moderately lipophilic, it can penetrate ocular tissues well, including the cornea and ciliary body, where it exerts its main therapeutic effects.
Metabolism
Pilocarpine is primarily metabolized in the liver and plasma by hydrolysis and enzymatic degradation. It undergoes biotransformation into inactive metabolites, mainly through non-specific esterases. Hepatic metabolism is not heavily dependent on cytochrome P450 enzymes, which reduces the risk of major drug–drug interactions via that pathway.
Elimination
Pilocarpine and its metabolites are eliminated mainly through the kidneys in urine. It has a relatively short half-life (about 0.75 to 1 hour), which leads to rapid clearance from the body. Because of this quick renal excretion and metabolic breakdown, repeated dosing is often required to maintain its therapeutic effect.
PHARMACODYNAMICS
Pilocarpine is a direct-acting muscarinic receptor agonist that primarily stimulates M3 (and to a lesser extent M1 and M2) receptors, producing parasympathetic nervous system effects. In the eye, activation of M3 receptors on the ciliary muscle causes contraction, which opens the trabecular meshwork and increases aqueous humor outflow, thereby lowering intraocular pressure in glaucoma. It also causes contraction of the iris sphincter muscle, leading to miosis (pupil constriction).
ADMINISTRATION
Pilocarpine is administered in different forms depending on the condition being treated. For glaucoma, it is commonly given as ophthalmic eye drops, typically instilled directly into the eye several times a day. The drops act locally to reduce intraocular pressure by increasing aqueous humor outflow. For xerostomia (dry mouth), pilocarpine is given orally in tablet form, usually in divided doses throughout the day to stimulate saliva production. In all forms, dosing is individualized based on patient response and tolerance, since excessive cholinergic effects may occur with higher doses.
DOSAGE AND STRENGTH
Pilocarpine is available as ophthalmic eye drops in strengths of 1% to 4% for the treatment of glaucoma, where it is instilled several times daily to reduce intraocular pressure. For xerostomia, it is given orally as 5 mg tablets, usually taken three to four times a day depending on patient response and tolerance. Dosage is individualized to balance therapeutic effect with the risk of cholinergic side effects.
DRUG INTERACTIONS
Pilocarpine has clinically important interactions mainly due to its cholinergic (parasympathetic) effects. Its effects may be reduced by anticholinergic drugs such as atropine, antihistamines, tricyclic antidepressants, and antipsychotics because these block muscarinic receptors
FOOD INTERACTIONS
Pilocarpine has no significant food interactions. Taking it with food may slightly delay absorption but does not reduce its effect, and food can sometimes help reduce mild gastrointestinal side effects like nausea.
CONTRAINDICATIONS
Pilocarpine is contraindicated in patients with conditions such as uncontrolled asthma or COPD due to the risk of bronchoconstriction, as well as in those with significant bradycardia, hypotension, or heart block. It should also be avoided in acute iritis and certain gastrointestinal conditions like intestinal obstruction because of its strong parasympathetic effects.
SIDE EFFECTS
Abdominal cramps
Blurred vision
Eye pain
Miosis (pupil constriction)
Bradycardia
Hypotension
Bronchospasm
OVER DOSAGE
Excessive sweating and salivation
Severe nausea, vomiting, diarrhea
Abdominal cramps
Marked bradycardia
Hypotension
TOXICITY
Pilocarpine occurs due to excessive muscarinic stimulation leading to cholinergic effects. It may present with severe sweating, salivation, nausea, vomiting, diarrhea, abdominal cramps, bronchospasm, bradycardia, and hypotension. In serious cases, it can progress to respiratory distress, cardiovascular collapse, and potentially life-threatening outcomes if not treated promptly.
