Topical anesthetic agents

Soliman MM, Macky TA, Samir MK. Comparative clinical trial of topical anesthetic agents in cataract surgery lidocaine 2% gel, bupivacaine 0.5% drops, and benoxinate 0.4% drops. J Cataract Refract Surg. 2004 30 1716-1720. 

Whatever the mechanisms responsible for bronchial hyperreactivity, bronchoconstriction itself seems to result not simply from the direct effect of the released mediators but also from their activation of neural or humoral pathways. Evidence for the importance of neural pathways stems largely from studies of laboratory animals. Thus, the bronchospasm provoked in dogs by histamine can be greatly reduced by pretreatment with an inhaled topical anesthetic agent, by transection of the vagus nerves, and by pretreatment with atropine. Studies of asthmatic humans, however, have shown that treatment with atropine causes only a reduction in—not abolition of—the... 

Topical anesthetic agents are selected for their ability to diffuse into the oral mucosa. Because many anesthetics used effectively for nerve block or infiltration do not adequately cross the mucosa, they cannot be used for topical anesthesia. 

Topical anesthetic agents decrease the sensitivity of nerve endings on skin surfaces. Topical anesthetic agents are in the form of solutions, liquid spray, ointment, creams, and gels. 

Some anesthetics are either too irritating or too ineffective to be applied to the eye. However, they are useful as topical anesthetic agents on the skin and/or mucous membranes. These preparations are effective in the symptomatic relief of anal and genital pruritus, poison ivy rashes, and numerous... 

Benzocaine, an effective topical anesthetic agent, was synthesized by Ritsert in 1890 and was found to have good anesthetizing properties and low toxicity. Benzocaine, however, has limited water solubility except at low pH values because of the lack of a basic aliphatic amino group, thereby disallowing the preparation of pharmaceutically acceptable parenteral solutions. 

Topical anesthetic agents (see chart) are solutions, liquid sprays, ointments, creams, and gels that are applied to mucous membranes, broken or unbroken skin surfaces, and bums to decrease the sensitivity of nerve endings in the affected area. 

The first topical anesthetic agent was TAC, which is a combination of tetracaine, adrenaline (epinephrine), and cocaine, and was used for face and scalp lacerations. A version of TAC called LET is used today. LET is a combination of lidocaine, epinephrine, and tetracaine. Lidocaine replaced cocaine. LET gel is... 

Moreira LB, Kasetsuwan N, Sanchez D, Shah SS, LaBree L, McDonnell PJ. Toxicity of topical anesthetic agents to human keratocytes in vivo. J Cataract Refract Surg 1999 25(7) 975-80. 

Lidocaine hydrochloride [73-78-9] (Xylocaine), is the most versatile local anesthetic agent because of its moderate potency and duration of action, rapid onset, topical activity, and low toxicity. Its main indications are for infiltration, peripheral nerve blocks, extradural anesthesia, and in spinal anesthesia where a duration of 30 to 60 min is desirable. Because of its vasodilator activity, addition of the vasoconstrictor, epinephrine, increases the duration of action of Hdocaine markedly. It is also available in ointment or aerosol preparations for a variety of topical appHcations. 

Thus, acylation of 3(W,iV-dibutylamino)propanol (39) with p-nitrobenzoyl chloride affords the intermediate, 40. Reduction of the nitro group gives butacaine (41), an agent equipotent as cocaine as a topical anesthetic. 

Uses Intermediate for production of tetraethyl lead and ethyl cellulose topical anesthetic organic synthesis alkylating agent refrigeration analytical reagent solvent for phosphorus, sulfur, fats, oils, resins, and waxes insecticides. 

Uses Coolant and refrigerant herbicide and fumigant organic synthesis-methylating agent manufacturing of silicone polymers, pharmaceuticals, tetramethyl lead, synthetic rubber, methyl cellulose, agricultural chemicals and nonflammable films preparation of methylene chloride, carbon tetrachloride, chloroform low temperature solvent and extractant catalytic carrier for butyl rubber polymerization topical anesthetic fluid for thermometric and thermostatic equipment. 

Benzocaine Street Names Coco snow, flat chucks and potato chips (crack cut w/ benzocaine) Use Cutting agent for crack (increases bulk of product and gives a numbing effect like cocaine) topical OTC anesthetic (brands many OTC topical forms) Actions Topical anesthetic used in many OTC products Effects Methemoglobinemia from excess topical or oral use. Over application of topical oral agents can impair gag reflex... 

The vasoconstrictor actions of epinephrine and norepinephrine have been used to prolong the action of local anesthetics by reducing local blood flow in the region of the injection. Epinephrine has been used as a topical hemostatic agent for the control of local hemorrhage. Norepinephrine is infused intravenously to combat systemic hypotension during spinal anesthesia or other hypotensive conditions in which peripheral resistance is low, but it is not used to combat the hypotension due to most types of shock. In shock, marked sympathetic activity is already present, and perfusion of organs, such as the kidneys, may be jeopardized by norepinephrine administration. 

The first clinical uses of a local anesthetic agent occurred in 1884, when cocaine was employed as a topical agent for eye surgery and to produce a nerve block. These events inaugurated a new era, that of regional anesthesia. New applications were developed, including spinal, epidural, and caudal anesthesia. The search for a better local anesthetic led to chemical synthesis of a number of other compounds that have more selective local anesthetic properties and few systemic side effects. 

Tetracaine hydrochloride (Pontocaine) is an ester of PABA that is an effective topical local anesthetic agent... 

Physical therapists may encounter the use of local anesthetics in several patient situations because of their various clinical applications. For example, therapists may be directly involved in the topical or transdermal administration of local anesthetics. As discussed earlier, repeated topical application of local anesthetics may help produce long-term improvements in motor function in patients with skeletal muscle hypertonicity, so therapists may want to consider incorporating topical anesthetics into the treatment of certain patients with CNS dysfunction. Therapists may also administer local anesthetics transdermally, using the techniques of iontophoresis and phonophoresis. Agents such as lido-caine can be administered through this method for the treatment of acute inflammation in bursitis, tendinitis, and so on. 

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