|Indications and Usage
||Benzocaine is a colorless trapezial crystal. Its melting point is 92℃ (88-90℃), boiling point is 183-184°C (1.87kPa). 1g of this drug is soluble in about 2500ml water, 5ml ethanol, 2ml chloroform, 4ml ether or 30-50ml almond oil and olive oil, and it is also soluble in dilute acid. It is stable in air, odorless, and slightly bitter.|
Benzocaine is a lipid-soluble surface anesthetic, and it weaker than other local anesthetics such as lidocaine and tetracaine, so it will not cause any discomfort due to its anesthetizing effects when acting on mucosa. Benzocaine is a type of drug with relatively strong lipid-solubility and will bind with mucosa and the fatty layer of skin, but it will not easily penetrate into the body and cause poisoning. Benzocaine can be used as a precursor for Ossur imitation, orthocaine, and procaine. It is also used as a local anesthetic and can stop pain and itching. It is mainly used in pain and itch prevention on wounds, ulcer surfaces, mucous membrane surfaces and hemorrhoids. Its paste form can also lubricate and stop pain for the nasopharynx and endoscope. Benzocaine’s aural solution is used to alleviate acute congestion, concentrated otitis externa, and the pain and itching of swimming otitis. Benzocaine is also effective for toothaches, sore throat, oral ulcers, all kinds of hemorrhoids, anal fissures, and vulvar itching. Benzocaine can be used as a male sex organ numbing agent to slow ejaculation. It can also be used as a numbing lubricant for the pharynx and endoscope, and it can be used as a UV absorbing agent for cosmetics.
- 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.
||the synthesis of benzocaine is carried out by the acid-catalyzed esterification of 4-aminobenzoic acid with ethanol:|
In a 5-mL round bottom flask, add 120 mg of 4-aminobenzoic acid (often called PABA for paminobenzoic acid), 1.5 mL of absolute ethanol (absolute ethanol is completely free of water and can be found on the hooded shevles), and 3 boiling chips. Heat this mixture on a sand bath until all the solid dissolves. Cool in ice and then add 0.25 mL of concentrated sulfuric acid dropwise. (One drop at a time.) A large amount of precipitate will form when the sulfuric acid is added, but this will dissolve during the reflux that follows. Attach an air condenser from the microscale kit, and reflux gently for 60- 75 min. Check periodically to be sure that the mixture is refluxing gently, and that the ring of condensation of solvent lies somewhere along the inner surface of the air condenser; loss of solvent will cause overheating and a significant decrease in yield.
||white odourless crystals|
||Benzocaine is used as an anesthetic (local).|