Tetracaine
**Tetracaine** (also known as **amethocaine**) is a topical local anaesthetic used primarily for the desensitization of the ocular surface (cornea and conjunctival sac). > **Clinical Pearl:** Although effective, it is uncommonly used in small animal practice because it tends to cause more marked conjunctival irritation and pain on application compared to alternatives like proxymetacaine. It must never be dispensed for ongoing therapeutic use due to severe corneal toxicity.
Mechanism: Local anaesthetic action is dependent on the reversible blockade of the **voltage-gated sodium channels** → prevents the influx of sodium → inhibits the propagation of an action potential along the nerve fibre. Sensory nerve fibres are blocked before motor nerve fibres, allowing a selective sensory blockade at low doses.
Dosing by species
- Local anaesthesia of the ocular surface · 1 drop per eye · topical · single application · single dose · Uncommonly used; proxymetacaine is advised as an alternative.
- Local anaesthesia of the ocular surface · 1 drop per eye · topical · single application · single dose · Uncommonly used; proxymetacaine is advised as an alternative.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Therapeutic use (repeated administration for pain relief)
- Application prior to a Schirmer tear test
Adverse effects
- Marked conjunctival irritation
- Chemosis
- Pain on application
- Corneal epithelial toxicity
- Delayed healing of corneal ulcers
Monitoring
- Corneal integrity (fluorescein staining if corneal damage is suspected)
Overdose
Overdosage in a clinical setting typically presents as local toxicity rather than systemic effects. Repeated administration leads to severe **corneal epithelial toxicity**, delayed healing of corneal ulcers, and potential corneal melting. > **Do not use for therapeutic purposes.**
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.