1. Clinical Overview
Proparacaine is a potent, rapid-acting, ester-type topical ophthalmic anesthetic. It is a para-aminobenzoic acid (PABA) derivative, structurally related to tetracaine. It is used exclusively for surface anesthesia of the eye for diagnostic and minor surgical procedures. It is not indicated for prolonged use or self-medication.
| Onset | Duration | Bioavailability |
|---|---|---|
| Within 13-30 seconds. | Approximately 15-20 minutes. | Negligible systemic absorption when used topically in the eye as intended. Primarily acts locally. |
2. Mechanism of Action
Proparacaine reversibly blocks the generation and conduction of nerve impulses by decreasing the permeability of neuronal membranes to sodium ions. This inhibition of sodium influx during depolarization prevents the initiation and propagation of action potentials, resulting in a reversible loss of sensation (anesthesia) in the corneal and conjunctival tissues.
3. Indications & Uses
- Topical anesthesia for tonometry (measurement of intraocular pressure)
- Removal of foreign bodies and sutures from the cornea/conjunctiva
- Short ophthalmic surgical procedures (e.g., cataract surgery, as an adjunct)
4. Dosage & Administration
Adult Dosage: For tonometry: 1-2 drops instilled into the conjunctival sac just prior to measurement. For foreign body removal or short procedures: 1-2 drops every 5-10 minutes for 1 to 3 doses as required.
Administration: Wash hands. Tilt head back, pull down lower eyelid to form a pouch. Instill the prescribed number of drops. Avoid touching the dropper tip to the eye, eyelids, or any surface. Close eyes gently for 1-2 minutes. Apply gentle pressure to the lacrimal sac (inner corner of eye) for about 1 minute to minimize systemic absorption. Do not blink excessively.
5. Side Effects
Common side effects may include:
- Transient stinging, burning, or discomfort upon instillation (usually mild)
- Conjunctival hyperemia (redness)
- Superficial punctate keratitis (with repeated use)
- Corneal epithelial edema (clouding).
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Sulfonamides (e.g., Sulfacetamide eye drops) | The metabolite PABA may antagonize the antibacterial effect of sulfonamides. | Moderate |
| Cholinesterase inhibitors (e.g., Echothiophate iodide eye drops) | Theoretically may reduce the metabolism of proparacaine, potentially increasing its duration and toxicity. Clinical significance is unclear. | Low |
7. Patient Counselling
- DO use only as directed by your eye doctor.
- DO NOT use more frequently or for longer than prescribed.
- DO NOT touch the dropper tip to your eye or any surface.
- DO NOT use if the solution is discolored or contains particles.
- DO NOT wear contact lenses while using this medication.
- DO apply gentle pressure on the inner corner of your eye for a minute after instillation.
8. Toxicology & Storage
Overdose: Ocular: Severe corneal damage, stromal edema, epithelial sloughing, ulceration, perforation, permanent vision loss. Systemic (from accidental ingestion or massive ocular exposure): CNS effects (dizziness, nervousness, tremors, convulsions, respiratory depression), Cardiovascular effects (bradycardia, hypotension, cardiac arrest).
Storage: Store at room temperature (15°C to 25°C). Protect from light. Do not freeze. Keep the bottle tightly closed when not in use. Keep out of reach of children. Discard the bottle 28 days after first opening to prevent contamination.