Benzocaine

Benzocaine is a local anaesthetic of the ester type with a poor solubility in water. The drug benzocaine is normally used as a topical pain reliever or as a common ingredient in cough drops. Benzocaine is used in multiple forms including lotion, gel, liquid, lozenges, and sprays. When Benzocaine is applied in any form it temporarily numbs or blocks the nerve endings, which leads to a decreases in the amount of pain. It is used in cattle, sheep, swine and horses for local and prolonged low epidural anaesthesia. Standard therapeutic doses of benzocaine ranged from 150 to 750 mg per animal. Benzocaine is also currently used as surface anaesthetic as ointments (0.5% benzocaine) for wounds and ulcerated surfaces in horses, cattle and sheep applied twice a day until healing.

A commonly used topical pain reliever. Main active ingredient in anesthetic ointments.

Anesthetic;Na+ channel blocker

Benzocaine acts on the central nervous system, cardiovascular system, neuromuscular junctions and ganglion synapse. Its mechanism of action is to prevent the generation and conduction of the nerve impulse. Local anaesthetics block conduction by decreasing or preventing the large transient increase in the permeability of excitable membranes to Na+ that is produced by a slight depolarisation. This action of local anaesthetics is due to their direct interaction with voltage-sensitive Na+ channels. Benzocaine is mainly hydroxylated in the metabolite para-aminobenzoic acid (PABA) that inhibits the action of sulphonamides.

Benzocaine is distributed in the body, crosses the placenta and is metabolised in the liver and in the plasma by non-specific cholinesterases. Benzocaine and its main metabolite (para-aminobenzoic acid) are excreted into urine.

Benzocaine appears as a moderately toxic compound after single administration. The acute intraperitoneal LD50 value was 216 mg/kg bw in mice. Benzocaine may induce methemoglobinemia in several species such as sheep, cats and dogs.