Description
Benzocaine (ethyl p-aminobenzoate) is used topically by itself or in combination with menthol or
phenol in nonprescription dosage forms such as gels, creams, ointments, lotions, aerosols, and
lozenges to relieve pain or irritation caused by such conditions as sunburn, insect bites,
toothache, teething, cold sores or canker sores in or around the mouth, and fever blisters.
Benzocaine is a lipophilic local anesthetic agent with a short duration of action.
Like most amino ester-type local anesthetics, it is easily hydrolyzed by plasma cholinesterase.
Because of its low pKa, however, it is un-ionized under most physiological conditions and, therefore, can only bind
to the lipid side of the local anesthetic receptor. It also can easily cross membranes
into systemic circulation to cause systemic toxicities. Furthermore, being a PABA derivative, it
has similar allergenic properties to procaine and is contraindicated with sulfonamide antibacterial
agents.
Chemical Properties
white odourless crystals
Definition
ChEBI: Benzocaine is a benzoate ester having 4-aminobenzoic acid as the acid component and ethanol as the alcohol component. A surface anaesthetic, it is used to suppress the gag reflex, and as a lubricant and topical anaesthetic on the larynx, mouth, nasal cavity, respiratory tract, oesophagus, rectum, urinary tract, and vagina. It has a role as a topical anaesthetic, an antipruritic drug, an allergen and a sensitiser. It is a benzoate ester and a substituted aniline.
Brand name
Americaine (Fisons); Baby
Anbesol (Whitehall-Robins).
Biological Functions
Benzocaine is a PABA derivative used primarily for
topical application to skin and mucous membranes. Its
low aqueous solubility allows it to stay at the site of application
for long periods. Its minimal rate of absorption
after topical administration is associated with a low incidence
of systemic toxicity. Benzocaine is contraindicated
in patients with known sensitivity to ester-linked
anesthetics or PABA-containing compounds.
General Description
Benzocaine is a unique local anesthetic because it does notcontain a tertiary amine. The pKa of the aromatic amine is 3.5ensuring that benzocaine is uncharged at physiological pH.Because it is uncharged, it is not water soluble but is ideal fortopical applications. The onset of action is within 30 secondsand the duration of drug action is 10 to 15 minutes.
Biochem/physiol Actions
Benzocaine is the ethyl ester of p-aminobenzoic acid (PABA). Benzocaine acts to inhibit the voltage-dependent sodium channels (VDSCs) on the nerve membrane, stopping the propagation of the action potential.
Clinical Use
Benzocaine is used for endoscopy, bronchoscopy, and topicalanesthesia. Benzocaine is available as a 20% solution topicalspray, in a 1% gel for mucous membrane application, and a14% glycerin suspension for topical use in the outer ear.Toxicity to benzocaine can occur when the topical doseexceeds 200 to 300 mg resulting in methemoglobinemia.Infants and children are more susceptible to this and methemoglobinemiahas been reported after benzocaine lubricationof endotracheal tubes and after topical administration to treata painful diaper rash.
Synthesis
Benzocaine is the ethyl ester of 4-aminobenzoic acid (2.3.1). The classic,
optimal way of benzocaine synthesis is the reduction of the nitro group of the ethyl ester
of 4-nitrobenzoic acid to benzocaine by hydrogen, which generates directly in the reaction
medium by the reaction of iron filings with dilute acids [24¨C26].
storage
Store at -20°C,protect from light
Purification Methods
Crystallise Benzocaine from EtOH/H2O or EtOH (m 93-94o), and dry it in air. [Beilstein 14 H 422, 14 IV 1129.]
Structure and conformation
Ethyl aminobenzoate, a para-aminobenzoate derivative (PABA)
