Topical local anesthetics

Once the cocaine has been legally produced from the coca leaf, it is exported to various countries for medicinal use, basically as a topical local anesthetic (applied to the surface, not injected, only treating a particular area). In the United States the crystalline powder is imported to pharmaceutical companies who process and package the cocaine for medical use. Merck Pharmaceutical Company and Mallinckrodt Chemical Works distribute cocaine in crystalline form (Hydrochloride Salt) in dark colored glass bottles to pharmacies and hospitals throughout the United States. Cocaine, in the alkaloid form (base drug containing no additives such as hydrochloride in the crystalline form) is rarely used for medicinal purposes. Cocaine hydrochloride crystals or flakes come in Vs, A and 1 ounce bottles from the manufacturer and has a wholesale price of approximately 20 to 25 per ounce (100% pure). 

Cocaine is still a drug of choice among many physicians as a topical local anesthetic because the drug has vasoconstrictive qualities (shrinks and stops the flow of blood). Synthetic local anesthetics such as novacaine and xylocaine (lidocaine) have also been discovered and used extensively as a local anesthetic. 

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

Cocaine did have genuine medical value as a topical (local) anesthetic, but it would be replaced later with similar chemicals (such as novocaine and lidocaine) that did not affect the brain. 

Topical anesthesia in the eye is relatively safe in controlled circumstances, when administered correctly (SEDA-20, 127). There does not seem to be any benefit in warming topical local anesthetic solutions before use (326). 

Local anesthetics that act by reducing the temperature of the area being anesthetized arc largely of historical interc.st. Most of the chemical agents used, however, pnxlucc intense cold through rapid evaporation and, hence, an anesthetic action. One of the most effective was ethyl chloride, which is still in use today us a topical local anesthetic. This agent should not be u.sed on mucous membranes or broken skin, however, and prolonged u.se may cause chemical frostbite. 

Dyclonine, a topical local anesthetic, is indicated in the relief of pain and itching from minor bums, insect bites, or irritations, or episiotomy or anogenital lesion and in anesthetizing mucous membranes before endoscopic procedures such as laryngoscopy and bronchoscopy, or endotracheal procedures. For example, for bronchoscopy, dyclonine (1% solution) is sprayed into the larynx and trachea every 5 minutes until laryngeal reflex is abolished. Dyclonine blocks conduction of impulses at the sensory nerve endings by altering cell membrane permeability to ionic transfer. 

Lidocaine hydrochloride is a topical/local anesthetic preparation. It stabilizes neuronal membranes by inhibiting the ionic fluxes required for the initiation and conduction of impulses, thereby affecting local anesthetic action. It is indicated as a topical anesthetic for use on normal intact skin for local analgesia or genital mucous membranes for superficial minor surgery and as pretreatment for inhltration anesthesia... 

The use of injectahle and topical local anesthetics may have a paUiative role in treatment of the immediate post-operative period, residting in more effective treatment of pain. Generally, these agents have short durations of action however, continuous infusions and potentially longer-acting agents (3-5 days) have merit. While somewhat less effective, patches and creams may be beneficial in some patients. 

Sensory systems Eyes Photorefractive keratectomy is a widely performed procedure for improving visual acuity. There are various regimens of medication for postoperative pain management, including the use of oral medications, topical non-steroidal antiinflammatory drugs, and local anesthetic solutions. The risk associated with long-term use of topical local anesthetic solutions has been highlighted [48 ]. 

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. 

Sorbitan sesquioleate emulsions of petrolatum and wax are used as ointment vehicles in skin treatment. In topical appHcations, the inclusion of both sorbitan fatty esters and their poly(oxyethylene) derivatives modifies the rate of release and promotes the absorption of antibiotics, antiseptics, local anesthetics, vasoconstrictors, and other medications from suppositories, ointments, and lotions. Poly(oxyethylene(20)) sorbitan monooleate, also known as Polysorbate 80 (USP 23), has been used to promote absorption of ingested fats from the intestine (245). 

The various methods of administering a local anesthetic include topical application, local infiltration, or regional anesfliesia... 

Topical anesfliesia involves die application of die anes-flietic to die surface of the skin, open area, or mucous membrane The anesthetic may be applied wifli a cotton swab or sprayed on the area This type of anesthesia may be used to desensitize the skin or mucous membrane to the injection of a deeper local anesthetic. In some instances, topical anesthetics may be applied by the nurse ... 

Topical anesthetics temporarily inhibit the conduction of impulses from sensory nerve fibers. These drug s may be used to relieve itching and pain due to skin conditions, such as minor bums, fungus infections, insect bites, rashes, sunburn, and plant poisoning, such as poison ivy. Some are applied to mucous membranes as local anesthetics. Examples of local anesthetics include benzocaine (Lanacane), dibucadne (Nupereainal), and lidocaine (Xylocadne). 

Nonprescription topical anesthetics such as lidocaine and benzocaine are available in many types of products. Local anesthetics decrease discharges in superficial somatic nerves and cause numbness on the skin surface but do not penetrate deeper structures such as muscle where the pain often lies. 

Several topically applied local anesthetics are routinely used by the eye care specialist in certain routine diagnostic procedures and for various relatively simple surgical procedures such as insertion of punctal plugs and surgical vision correction. The first of these to be used was cocaine, in concentrations ranging from 1 to 4% [30]. More modern local anesthetics, however, such as tetracaine hydrochloride and proparacaine hydrochloride, have replaced cocaine as drugs of choice in these procedures. For surgical procedures of a more complex nature, lidocaine hydrochloride and similar local anesthetics as retrobulbar injections have been used [31]. 

Which of the following local anesthetics is useful for topical (surface)... 

Regional analgesia with local anesthetics (Table 54-6) can provide relief of both acute and chronic pain. Anesthetics can be positioned by injection (i.e., in joints, in the epidural or intrathecal space, along nerve roots) or applied topically. 

Local anesthetics are used for topical anesthesia, local infiltration, peripheral nerve block, paravertebral anesthesia, intravenous block also known as regional anesthesia, epidural block, and spinal i.e. subarachnoid blockade. The local anesthetics may be divided into two main groups, the esters and the amide-type agents. 

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. 

An important property of the ideal local anesthetic is low systemic toxicity at an effective concentration. Onset of action should be quick, and duration of action should be sufficient to allow time for the surgical procedure. The local anesthetic should be soluble in water and stable in solution. It should not deteriorate by the heat of sterilization, and it should be effective both when injected into tissue and when applied topically to mucous membranes. Its effects should be completely reversible. 

The rate of absorption of a local anesthetic into the bloodstream is affected by the dose administered, the vascularity at the site of injection, and the specific physicochemical properties of the drug itself. Local anesthetics gain entrance into the bloodstream by absorption from the injection site, direct intravenous injection, or absorption across the mucous membranes after topical application. Direct intravascular injection occurs accidentally when the needle used for infiltration of the local anesthetic lies within a blood vessel, or it occurs intentionally when Udocaine is used for the control of cardiac arrhythmias. 

Local anesthetics are used extensively on the mucous membranes in the nose, mouth, tracheobronchial tree, and urethra. The vasoconstriction produced by some local anesthetics, cocaine especially, adds a very important advantage to their use in the nose by preventing bleeding and inducing tissue shrinkage. Topical anesthesia permits many diagnostic procedures in the awake patient, and when it is combined with infiltration techniques, excellent anesthesia may be obtained for many... 

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