Overview
Tetracaine is a potent ester-type local anesthetic used primarily for topical anesthesia of mucous membranes and ophthalmic procedures. It acts by blocking sodium channels in nerve membranes, preventing nerve impulse generation and conduction. Tetracaine has a rapid onset (within 30 seconds for ophthalmic use) and longer duration of action compared to other topical anesthetics (up to 15-20 minutes). It is approximately 10 times more potent than procaine and has greater toxicity potential.
Mechanism of Action
Tetracaine is an ester-linked local anesthetic that blocks voltage-gated sodium channels in neuronal cell membranes. This inhibition prevents depolarization and subsequent propagation of action potentials along nerve fibers, resulting in reversible loss of sensation (anesthesia) in the affected area. The drug diffuses across nerve membranes in its uncharged base form, then re-equilibrates to the charged cationic form that binds to the sodium channel receptor site.
Indications
- Topical anesthesia of mucous membranes (oral, pharyngeal, laryngeal, nasal)
- Ophthalmic anesthesia for tonometry, gonioscopy, removal of foreign bodies, and short surgical procedures
- Spinal anesthesia (historically, though rarely used today)
- Diagnostic procedures involving mucosal surfaces
Dosage
Dosage varies by formulation and indication. For ophthalmic use: 1-2 drops of 0.5% solution instilled into conjunctival sac. For topical mucosal anesthesia: Apply 0.5-2% solution as needed, typically not exceeding 20 mg total dose (1 mL of 2% solution). Maximum recommended dose: 20 mg for topical administration. Always use the lowest effective dose for the shortest necessary duration.
Contraindications
- Hypersensitivity to tetracaine, other ester-type local anesthetics (procaine, chloroprocaine, benzocaine), or para-aminobenzoic acid (PABA) derivatives
- Trauma or infection at application site
- Ophthalmic use in patients with active ocular inflammation or infection
- Patients with known methemoglobinemia risk factors
- Concurrent use with sulfonamides (theoretical concern due to PABA metabolite)
Side Effects
- Ophthalmic: Transient stinging/burning, conjunctival redness, corneal epithelial changes, allergic reactions
- Topical mucosal: Bitter taste, numbness beyond intended area, transient stinging
- Systemic (with excessive absorption): CNS - dizziness, nervousness, blurred vision, tremors, seizures; Cardiovascular - hypotension, bradycardia, arrhythmias, cardiac arrest
- Hypersensitivity reactions: Contact dermatitis, urticaria, anaphylaxis
- Methemoglobinemia (rare)
Interactions
- Sulfonamides: Theoretical antagonism due to PABA metabolite of tetracaine
- Other local anesthetics: Additive toxicity risk
- Cholinesterase inhibitors (neostigmine, pyridostigmine): May decrease tetracaine metabolism
- Antiarrhythmics (class I): Additive cardiac effects
- MAO inhibitors, tricyclic antidepressants: May potentiate systemic effects