1. Clinical Overview
Pilocarpine (2% w/v) is a direct-acting cholinergic parasympathomimetic alkaloid, primarily used as a topical ophthalmic solution. It is a muscarinic receptor agonist that stimulates the sphincter pupillae and ciliary muscles, causing miosis (pupil constriction) and accommodation spasm. In the Indian context, it is a cornerstone treatment for primary open-angle glaucoma and ocular hypertension, often used when first-line prostaglandin analogues are insufficient or contraindicated. It is also a key diagnostic agent for Adie's tonic pupil.
| Onset | Duration | Bioavailability |
|---|---|---|
| Miosis begins within 10-30 minutes of topical ocular administration. | The miotic effect lasts for 4-8 hours, but intraocular pressure reduction may persist for up to 24 hours with repeated dosing. | Negligible systemic bioavailability following topical ocular administration due to minimal absorption into systemic circulation. |
2. Mechanism of Action
Pilocarpine is a direct-acting cholinergic agonist that binds to and activates muscarinic (M3) receptors on the iris sphincter muscle and the ciliary muscle. This causes contraction of the sphincter pupillae, leading to miosis, and contraction of the ciliary muscle, leading to accommodation. In glaucoma, the contraction of the ciliary muscle opens the trabecular meshwork, facilitating aqueous humor outflow and reducing intraocular pressure (IOP).
3. Indications & Uses
- Primary Open-Angle Glaucoma
- Ocular Hypertension
- Angle-Closure Glaucoma (acute and chronic management)
4. Dosage & Administration
Adult Dosage: One drop in the affected eye(s), up to 4 times daily. Frequency is adjusted based on IOP response. Often used 2-3 times daily.
Administration: Wash hands. Tilt head back, pull lower eyelid down to form a pouch. Instill one drop without touching the dropper tip to eye or any surface. Close eye gently and apply pressure to the nasolacrimal duct (inner corner of eye) for 1-2 minutes to minimize systemic absorption. Wait at least 5-10 minutes before instilling any other topical ophthalmic medication.
5. Side Effects
Common side effects may include:
- Transient stinging/burning/itching upon instillation
- Blurred vision (due to induced myopia from ciliary spasm)
- Headache/brow ache (especially in initial days)
- Miosis (pupil constriction)
- Conjunctival and ciliary congestion
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Topical Beta-blockers (Timolol, Betaxolol) | Additive lowering of IOP. Standard combination therapy. | Moderate |
| Other Cholinergic Agents (Carbachol, Echothiophate) | Additive parasympathomimetic effects and side effects. Avoid concurrent use. | Major |
| Anticholinergic Drugs (Atropine, Cyclopentolate, Tropicamide) | Pharmacological antagonism. Reduces miotic and IOP-lowering effect of pilocarpine. | Major |
| Systemic Beta-blockers, Digoxin | Increased risk of bradycardia and conduction defects if pilocarpine is systemically absorbed. | Moderate |
| Succinylcholine | Prolonged neuromuscular blockade possible. | Moderate |
7. Patient Counselling
- DO wash hands before use.
- DO apply pressure on the inner corner of the eye for 1-2 minutes after instillation.
- DO wait at least 5 minutes before using other eye drops.
- DO NOT touch the dropper tip to any surface to avoid contamination.
- DO NOT drive or operate machinery until vision clears.
- DO NOT wear soft contact lenses during treatment; the preservative (benzalkonium chloride) may be absorbed.
8. Toxicology & Storage
Overdose: TOPICAL OVERDOSE: Increased local side effects (severe miosis, blurred vision, pain). SYSTEMIC OVERDOSE (from accidental ingestion or extreme absorption): Profuse salivation, lacrimation, sweating, nausea, vomiting, diarrhea, bradycardia, hypotension, bronchospasm, tremors, and shock.
Storage: Store at controlled room temperature (15°C to 25°C). Protect from light. Keep the bottle tightly closed. Do not freeze. Keep out of reach of children. Discard the bottle 28 days after first opening to prevent contamination.