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Topical anesthetics are a local anesthetic used for the numbing of the surface of a body part. They can be used to numb any area of the skin as well as the front of the eyeball, the inside of the ear, nose or throat, the anus and the genital area. Topical anesthetics come in the form of creams, aerosols, ointments, lotions, sprays, and jellies. Examples of topical anesthetics include butamben, benzocaine, lidocaine, dibucaine, pramoxine, oxybuprocaine, proparacaine, pramoxine, proxymetacaine, and tetracaine.
Topical anesthetics are widely used in various medical and surgical subspecialties such as anesthesia, ophthalmology, otorhinolaryngology, dentistry, anesthetic surgery, and urology. They cause a temporary loss of pain sensation after its direct application. Their effectiveness and delivery may be enhanced by using free bases; by increasing the concentration of the drug, lowering the melting point; by using chemical and physical permeation enhances and lipid delivery vesicles. Many topical anesthetic agents are a eutectic mixture of local anesthetics. While using the topical anesthetics, careful attention must be given to their pharmacology, area, and duration of application, age and weight of the patients and their possible side effects.
Topical anesthetics reversibly block nerve conduction in the site of administration by targeting nerve endings in the mucosa or dermis, causing temporary loss of sensation in the application area. The conduction of nerve impulse is blocked by decreasing the permeability of nerve cell membrane to sodium ions by competing with sites of calcium-binding that control sodium permeability. The change in permeability decreases depolarization while increasing the excitability threshold until losing the ability to generate an action potential.
Topical anesthetics are typically used for the relief of itching and pain caused by various conditions such as sunburn and other minor burns, insect stings or bites, poison oak, poison ivy, poison sumac, and minor scratches and cuts.
Topical anesthetics are used in ophthalmology and optometry to numb the eye’s surface to allow:
In the field of dentistry, topical anesthetics are mainly used to numb oral tissue before the administration of a dental local anesthetic due to the entry of the needle into the soft tissues of the oral cavity.
Some types of topical anesthetics are also used in otolaryngology, such as oxybuprocaine.
Topical anesthetics are now used to the temporarily relieve premature ejaculation when applied to the glans of the penis. Benzocaine or lidocaine are typically used for this purpose as they are available as over-the-counter drugs.
The duration of topical anesthesia depends on the type and amount applied but is usually about half an hour.