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Tetracaine hydrochloride is a local anesthetic agent that has been in use since the early 1930s. It is an amino-ester class local anesthetic that is commonly used for short procedures on the surface of the eye, ears, and nose. It is also indicated for spinal anesthesia. The World Health Organization (WHO) lists tetracaine as an essential medication due to its relatively low cost compared to other local anesthetic agents.
Mechanism of Action: Tetracaine primarily functions by blocking intracellular sodium channels, which prevents sodium influx and, consequently, stops cellular depolarization and the development of action potentials. This blockade must occur at three successive nodes of Ranvier along an axon for nerve conduction to be impaired.
Administration: Tetracaine has a moderate pKa of 8.46 at room temperature and is known for its quick onset of action, particularly for intrathecal administration. It is highly lipid-soluble and has a moderate protein binding of 75%, which allows for a duration of action up to 200 minutes. The drug is metabolized primarily by plasma cholinesterase into an alcohol and para-aminobenzoic acid (PABA), with a minimal amount excreted unmetabolized in the urine.
Dosage: It is recommended not to exceed 1.5 to 3 mg/kg of actual patient weight for dosing. The toxicity of the drug is affected by the site of administration, with absorption occurring fastest via the IV route and slowest via the subcutaneous route.
