What is Tetracaine?
Tetracaine is a type of amino ester local anaesthetic, which has a longer duration of action than benzocaine and lidocaine. It was released for medical use in 1941 and was hailed by the World Health Organization as 1 of the most effective and safe medicines needed in a health system. Local anaesthetics can be used for topical applications to numb the conjunctiva, skin, eardrum, and mucous membrane. Nowadays, it is rarely used for epidural anaesthesia or peripheral nerve blocks due to slow onset, potential toxicity in high doses, and profound motor blockade.
Tetracaine comes in a 0.5%, 1%, and 2% solution or as Niphanoid crystals. The crystal form is preferred because of the relative instability of tetracaine. A solution with 0.5% tetracaine hydrochloride is used as an ophthalmic solution for procedures requiring a rapid and short-acting topical anaesthesia.
Mechanism of Action
Tetracaine induces local anaesthesia by reversibly blocking the conduction in nerve fibres by reducing the permeability of the membrane to sodium (Na+) ions. This occurs when the drug binds to the voltage gated sodium channels inside the membrane. Tetracaine has variable systemic absorption; it is metabolised in the plasma by pseudocholinesterase and excreted in the urine.
The duration of tetracaine may be unreliable, thus it is often combined with a vasoconstrictor additive. These combinations can increase the anesthetic effects of this ester for up to 5 hours, but phenylephrine as an additive is associated with transient neurologic symptoms (TNS).
- Hypersensitivity to tetracaine and other ester local anaesthetics, sulfites, and PABA.
- Infection or inflammation at the injection site.
- Blood problems such as platelet abnormalities, thrombocytopenia, uncontrolled coagulopathy, and increased bleeding time.
This is a non-exhaustive list of adverse events associated with tetracaine use. Please refer to the product leaflet for a complete list of side effects and complications.
Tetracaine Side Effects
Common Side Effects
- Burning or stinging during application
- Skin rash
- Redness and swelling
- Sensitivity to light
Uncommon Side Effects
- Weakness or paralysis of lower extremities
- Total spinal block
- Urinary incontinence or retention
- Headache and back pain
- Loss of perineal sensation and sexual function
- Headache and back pain
Rare Side Effects
- Shortness of breath
- Swelling of the face and mouth
- Visual impairment
- Tetracaine-induced CNS toxicity (symptoms and depression and CNS stimulation)
- Cardiotoxic effects (angina, hypotension, palpitation, and cardiovascular collapse)
- Depression or cardiac excitability and contractility