Pilocarpine is a muscarinic cholinergic agonist derived from the South American shrub Pilocarpus jaborandi. It is primarily known for its use in the treatment of glaucoma and dry mouth (xerostomia), especially following radiation therapy for head and neck cancer.
Chemical Structure and Properties
Mechanism of Action
As a direct-acting cholinergic agonist, Pilocarpine exerts its effect by stimulating muscarinic receptors. In the eye, this action results in contraction of the ciliary muscle, leading to increased outflow of aqueous humor and a subsequent decrease in intraocular pressure. In salivary glands, Pilocarpine stimulates saliva production.
- Absorption: Pilocarpine is well absorbed when administered topically in the eye or orally.
- Distribution: It distributes widely in the body and can cross the blood-brain barrier due to its lipophilic nature.
- Metabolism: It is metabolized in the liver.
- Excretion: Primarily excreted in the urine.
- Glaucoma: Pilocarpine is used in the management of both acute angle-closure glaucoma and chronic open-angle glaucoma. It lowers intraocular pressure by facilitating aqueous humor outflow.
- Xerostomia: In patients with dry mouth following head and neck radiation or in Sjögren’s syndrome, Pilocarpine stimulates saliva production.
- Ocular Effects: When used in the eye, it can cause blurred vision, nearsightedness (myopia), and eye pain.
- Systemic Effects: Can include sweating, nausea, increased salivation, bronchial secretions, and gastrointestinal cramping due to generalized muscarinic activation.
- Cardiac Effects: Bradycardia is a potential side effect.
Contraindications and Precautions
- Asthma and COPD: Should be used cautiously in patients with bronchial asthma or chronic obstructive pulmonary disease.
- Cardiovascular Diseases: Caution is advised in patients with cardiovascular diseases, particularly those involving bradycardia.
- Cataracts: Pilocarpine-induced myopia may exacerbate cataract-related symptoms.
- Other Cholinergic Drugs: Concurrent use can potentiate the effects of Pilocarpine.
- Beta-Blockers: Co-administration with ocular beta-blockers in glaucoma therapy can enhance the reduction of intraocular pressure.
- Anticholinergic Medications: These can counteract the effects of Pilocarpine.
- Elderly Patients: May be more sensitive to the systemic effects of Pilocarpine.
- Administration in Eye Conditions: When used for glaucoma, the patient should be instructed on proper administration to maximize the drug’s effectiveness and minimize systemic absorption.
Pilocarpine is a valuable cholinergic agent, especially in the field of ophthalmology for the management of glaucoma. Its use in stimulating saliva production in xerostomia also highlights its versatility. However, its cholinergic properties necessitate careful monitoring for adverse effects and potential drug interactions.