Proxymetacaine
Proxymetacaine (also known as proparacaine) is a rapid-acting topical local anaesthetic used primarily on the ocular surface (cornea and conjunctival sac), as well as the external auditory meatus and nares. It acts rapidly (within 1 minute) and provides anaesthesia for 25-55 minutes depending on the species. > **Clinical Warning:** All topical anaesthetics are toxic to the corneal epithelium. Repeated application delays the healing of ulcers and can lead to severe corneal melting. **Never dispense for home use as a therapeutic analgesic.** **Clinical Pearl:** Serial application increases both the duration and depth of anaesthesia. Because topical anaesthetics block reflex tear production, they should not be applied prior to performing a Schirmer tear test.
Mechanism: Local anaesthetic action is dependent on the **reversible blockade of voltage-gated sodium channels** → prevents the influx of sodium ions → 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
- Ocular surface anaesthesia · 1-2 drops/eye · topical · PRN · Single application (or serial for depth) · Maximal effect at 15 min, duration 45-55 min.
- Aural/nasal anaesthesia · 5-10 drops/ear or nose · topical · q5-10min · Maximum 3 doses if used intranasally
- Ocular surface anaesthesia · 1-2 drops/eye · topical · PRN · Single application · Maximal effect at 15 min, duration 25 min.
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 (e.g., home pain management)
- Application prior to a Schirmer tear test
Adverse effects
- Conjunctival hyperaemia (common)
- Local irritation / chemosis (occasional)
- Corneal epithelial toxicity
- Delayed corneal ulcer healing
Monitoring
- Corneal integrity (fluorescein staining if damage is suspected)
- Resolution of anaesthesia (protect the eye from trauma while numb)
Overdose
Overdosage via repeated topical application leads to **severe corneal toxicity**, epithelial sloughing, delayed healing of ulcers, and potentially corneal melting. Systemic toxicity is rare with standard ophthalmic use but could theoretically cause CNS excitation followed by depression and cardiovascular collapse if massive amounts are absorbed through mucous membranes.
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.