Tetrakaiini

Tetrakaiini, known in English as tetracaine (also amethocaine), is an ester-type local anesthetic. It works by blocking voltage-gated sodium channels in nerve membranes, preventing the initiation and propagation of action potentials and thereby producing temporary loss of sensation in the area where it is applied. Compared with some other local anesthetics, tetracaine is relatively potent and has high lipid solubility.

Medical uses for tetrakaiini include topical anesthesia of the eye, where ophthalmic solutions (commonly around 0.5%) are used to numb the cornea for minor procedures such as tonometry, suturing, or diagnostic examinations. It is also employed as a topical mucosal anesthetic for certain ENT and dental procedures. In regional anesthesia, injectable forms of tetrakaiini can be used as part of spinal or epidural anesthesia, where it provides longer-lasting numbness than some alternatives.

Pharmacodynamics and pharmacokinetics: tetrakaiini acts quickly at the site of administration by diffusing into nerve membranes and blocking sodium channels. It is an ester, and its activity is rapidly terminated by hydrolysis in the plasma by cholinesterases, producing inactive metabolites that are excreted by the kidneys. Systemic exposure can occur in overdose or inadvertent intravascular administration, carrying a risk of central nervous system and cardiovascular toxicity.

Safety and adverse effects: local or systemic toxicity may manifest as circumoral numbness, dizziness, tinnitus, seizures, arrhythmias, or hypotension if absorbed in significant amounts. Allergic reactions to ester-type anesthetics are uncommon but possible. Tetrakaiini should be used with caution in patients with known hypersensitivity to local anesthetics, and dosing should be adjusted to avoid excessive plasma levels.

See also: local anesthetics, amethocaine, ophthalmic anesthesia.