Tetracaine (also known as amethocaine) is a local anesthetic of the ester anesthetic group. It is mainly used topically in ophthalmology and as an antipruritic, and it has been used in spinal anesthesia. In biomedical research, tetracaine is used to alter the function of calcium release channels (ryanodine receptors) that control the release of calcium from intracellular stores. Tetracaine is an allosteric blocker of channel function. At low concentrations, tetracaine causes an initial inhibition of spontaneous calcium release events, while at high concentrations, tetracaine blocks release completely. Tetracaine is the T in TAC, a mixture of 5 to 12 per cent tetracaine, 0.05 per cent adrenaline, and 4 or 10 per cent cocaine hydrochloride used in ear, nose & throat surgery and in the emergency department where numbing of the surface is needed rapidly, especially when children have been injured in the eye, ear, or other sensitive locations. It is on the World Health Organization's List of Essential Medicines, a list of the most important medication needed in a basic health system. A systematic review investigated tetracaine for use in emergency departments, especially for IV cannulation in children, in view of its analgesic and cost-saving properties. However, it did not find an improvement in first attempt cannulations.