Benzocaine is the ethylester 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.
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.
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.
Some condoms designed to prevent premature ejaculation. Benzocaine largely inhibits sensitivity on the penis, and can allow for an erection to be maintained longer (in a continuous act) by delaying ejaculation. Conversely, an erection will also fade faster if stimulus is interrupted.
Benzocaine mucoadhesive patches have been used in reducing orthodontic pain.
In Poland it is included, together with menthol and zinc oxide, in the liquid powder (not to be confused with the liquid face powder) used mainly after mosquito stings. Today's ready made Pudroderm was once used there as pharmaceutical compound.
Benzocaine is commonly found, particularly in Britain, as an impurity in street cocaine and also as a bulking agent in "legal highs". Whilst giving a numbing effect similar to cocaine on users' gums it does not actually produce the effects of cocaine.
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^Ritsert, E. (1925) "Über den Werdegang des Anästhesins" (On the development of Anästhesin), Pharmazeutische Zeitung, vol. 60, pages 1006–1008. See also: Christoph Friedrich and Magdalena Klimonow, "150. Geburtstag: Eduard Ritsert und das Anaesthesin" (150th birthday: Eduard Ritsert and Anästhetsin [Benzocaine]"), Pharmazeutische Zeitung online. First published clinical study demonstrating the efficacy of benzocaine: Noorden, C. v. (1902) "Ueber para-Aminobenzoesäure-Ester als locales Anästhetikum" (On [an] ester of para-aminobenzoic acid as a local anaesthetic), Klinische Wochenschrift, vol. 39, pages 373–375.
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^Lexicomp Online, Adult and Pediatric Lexi-Drugs Online, Hudson, Ohio: Lexi-Comp, Inc.; 2013; April 15, 2013.
^Food and Drug Administration. FDA Public Health Advisory: Life-threatening side effects with use of skin products containing numbing ingredients for cosmetic procedures. 2007 Feb 6, updated 2007 Feb 9. From FDA website
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^Eslamian L, Borzabadi-Farahani A, Edini HZ, Badiee MR, Lynch E, Mortazavi A (2013). "The analgesic effect of benzocaine mucoadhesive patches on orthodontic pain caused by elastomeric separators, a preliminary study.". Acta Odontol Scand. 71 (5): 1168–73. doi:10.3109/00016357.2012.757358. PMID23301559.
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