AHFS/Drugs.com Monograph | ||
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Trade names Anbesol, Cepacol, Lanacane, Orajel Pregnancycategory US: C (Risk not ruled out) ATC code C05AD03 (WHO) D04AB04 (WHO), QN01AX92 (WHO), N01BA05 (WHO), R02AD01 (WHO) Legal status UK: General sales list (GSL, OTC)US: OTC | ||
Benzocaine is a local anesthetic commonly used as a topical pain reliever or in cough drops. It is the active ingredient in many over-the-counter anesthetic ointments such as products for oral ulcers. It is also combined with antipyrine to form A/B otic drops to relieve ear pain and remove earwax.
Contents
Chemical properties
Benzocaine is the ethyl ester of p-aminobenzoic acid (PABA). It can be prepared from PABA and ethanol by Fischer esterification or via the reduction of ethyl p-nitrobenzoate. Benzocaine is sparingly soluble in water; it is more soluble in dilute acids and very soluble in ethanol, chloroform and ethyl ether. The melting point of benzocaine is 88–90 °C, and the boiling point is about 310 °C. The density of benzocaine is 1.17 g/cm3.
History
Benzocaine was first synthesized in 1890 by the German chemist Eduard Ritsert (1859–1946), in the town of Eberbach and introduced to the market in 1902 under the name "Anästhesin".
Mechanism of action
Pain is caused by the stimulation of free nerve endings. When the nerve endings are stimulated, sodium enters the neuron, causing depolarization of the nerve and subsequent initiation of an action potential. The action potential is propagated down the nerve toward the central nervous system, which interprets this as pain. Benzocaine acts to inhibit the voltage-dependent sodium channels (VDSCs) on the neuron membrane, stopping the propagation of the action potential.
Uses
Benzocaine is indicated to treat a variety of pain-related conditions. It may be used for:
Formulations
Benzocaine can come in a variety of preparations including:
Oral preparations:
Topical preparations:
Otic preparations:
Side effects
Benzocaine is generally well-tolerated and non-toxic when applied topically as recommended.
However, there have been reports of serious, life-threatening adverse effects (e.g., seizures, coma, irregular heart beat, respiratory depression) with over-application of topical products or when applying topical products that contain high concentrations of benzocaine to the skin.
Over-application of oral anesthetics such as benzocaine can increase the risk of pulmonary aspiration by relaxing the gag-reflex and allowing regurgitated stomach contents or oral secretions to enter the airway. Applying an oral anesthetic and consuming beverages before going to bed can be particularly hazardous.
The topical use of higher concentration (14-20%) benzocaine spray products applied to the mouth or mucous membranes has been found to be a cause of methemoglobinemia, a disorder in which the amount of oxygen carried by the blood is greatly reduced. This side effect is most common in children under 2 years of age. As a result, the FDA has stated that benzocaine products should not be used in children under 2 years of age, unless directed by and supervised by a healthcare professional. Symptoms of methemoglobinemia usually occur within minutes to hours of applying benzocaine, and can occur upon the first-time use or after additional use.
Benzocaine may cause allergic reactions. These include:
Other uses
Benzocaine is used as a key ingredient in numerous pharmaceuticals:
Synthesis
Benzocaine can be prepared by esterification using 4-aminobenzoic acid and ethanol. It can also be prepared by reduction of ethyl 4-nitrobenzoate to the amine.
In industrial practice, the reducing agent is usually iron and water in the presence of a little acid.