CHAPTER 10 Topical Anesthesia

Topical anesthesia offers patients an alternative to local injectable anesthetics. The ideal topical anesthetic should provide 100% anesthesia with rapid onset of action, have prolonged duration, and have no local or systemic side effects. To date, the perfect topical agent has not been developed. New formulations have improved efficacy and application options. (Also see Chapter 4, Local Anesthesia; Chapter 229, Transcutaneous Electrical Nerve Stimulation, Phonophoresis, and Iontophoresis; and Chapter 5, Local and Topical Anesthetic Complications.)

There are many benefits and some drawbacks of topical anesthetics compared with local injectable anesthetics. First, application of topical anesthetics is painless. In addition, topical anesthetics do not distort wound margins in laceration repairs. One drawback is the extra time required to achieve effective anesthetic effect.

Although the first topical anesthetics were developed in the latter half of the 19th century with the first uses of topical cocaine, safer and more effective agents have more recently become available. The use of TAC (tetracaine, adrenalin, cocaine), one of the first topical anesthetic creams to be developed, is no longer supported by the literature. LET/LAT (lidocaine, epinephrine/adrenalin, tetracaine) solution-gel has been found to be equally efficacious as TAC. LET eliminates cocaine (thus lessening the risk for toxicity and seizures), avoids documentation issues, and lowers the cost.

EMLA (eutectic mixture of local anesthetics), which was approved by the U.S. Food and Drug Administration (FDA) in 1992, is now commonly used. A eutectic mixture is one in which the melting point of the mixture is lower than that of the individual components; in the case of EMLA, the components (lidocaine and prilocaine) remain liquid at room temperature. LMX 4 (4% liposomal lidocaine) and LMX 5 (5% liposomal lidocaine) are liposomal agents that are available over the counter. LMX 4 and LMX 5 were formerly called ELA-Max. Liposomes are synthetic biologic membranes composed of an aqueous core surrounded by a lipid layer. This delivery system allows medications to penetrate the stratum corneum more readily because they resemble cell membranes, thus strengthening the onset of action while controlling release of the action drug for a longer duration of action.

More recently, the S-Caine Patch has been developed. This 1 : 1 eutectic mixture of 70 mg lidocaine and 70 mg tetracaine base has a disposable, oxygen-activated heating element. The heat is maintained at 39° C to 41° C for a 2-hour period. Heat has been shown to enhance the delivery of topical creams.

Categories of topical anesthetics can be divided into those applied on intact skin, nonintact skin, and mucous membranes. This categorization is important because a topical anesthetic (e.g., lidocaine) applied to the mucous membrane may result in blood levels comparable with those achieved with parenteral administration (Table 10-1). Available topical anesthetics for intact skin are EMLA/EMLA Disc, LMX 4, LMX 5, and iontophoretic preparations. Also, with the development of many new aesthetic procedures, many clinicians now have various mixtures compounded (see later, as well as Chapter 59, Skin Peels).

TABLE 10-1 Summary of Topical Anesthetics

In addition to creams and ointments, cooling can also be used to provide brief, temporary anesthesia (e.g., ethyl chloride spray or ice cubes).

Indications

Intact Skin

LMX 4/LMX 5

• FDA: temporary relief of pain associated with minor cuts, abrasions, minor burns, skin irritation, and insect bites.

• Literature-supported uses: venipuncture, venous cannulation, arterial puncture, suture removal, shave biopsy, punch biopsy, chemical peels, curettage of molluscum contagiosum, cryotherapy of venereal warts, intracutaneous allergy testing, epilation, débridement of otitis media with an intact tympanic membrane, removal of an embedded foreign body, circumcision at more than a 37-week gestation, skin grafting, débridement of ulcers, lumbar puncture.

• Adjunct to: vasectomy, dermabrasion, laser resurfacing, postsurgical discomfort.

• Nonsurgical uses: postherpetic neuralgia, meralgia paresthetica.

• Used for intact skin. Efficacy is similar to EMLA, but LMX 4 is less expensive than EMLA.

EMLA

FDA: for use on intact skin for local anesthesia.

Lidoderm Patch

FDA: relief of pain associated with postherpetic neuralgia.

BLT Triple Anesthetic Gel (20% Benzocaine, 6% Lidocaine, 4% Tetracaine)

• Used for intact skin.

• Percentages may vary.

• This is usually compounded.

S-Caine Patch/S-Caine Peel

• Used for intact skin.

• Approved for children 3 years of age or older.

Nonintact Skin

Topicaine (4% or 5% Lidocaine Gel)

• Minor skin cuts or abrasions.

• Available over the counter.

LET/LAT (Lidocaine, Epinephrine/Adrenalin, Tetracaine)

• Scalp and facial lacerations.

• Does not work on intact skin.

Mucous Membranes

Lidocaine (Xylocaine), Benzocaine

• Painful, irritated, inflamed mucous membranes: anesthesia before minor surgical procedure and esophagogastroduodenoscopy.

• 2% viscous lidocaine for aphthous ulcers and mucositis in immunosuppressed patients.

Ophthalmic Preparations

Removal of foreign bodies, short eyelid procedures (e.g., chalazion removal), and placement of eye shields.

Mechanical Methods

Thermal: Ice/Ethyl Chloride Spray

Skin tag clipping, incision and drainage of simple abscess, and injections (blood draws, skin grafting, sports injuries).

For Aesthetic Procedures

Many noninvasive aesthetic procedures (e.g., deep skin peels, facial resurfacing) require some type of topical anesthetic. Oral analgesic medications and anxiolytics can also be beneficial. Everyone seems to have his or her own favorite compounded preparation. With the rapid growth of procedures in this field, few studies have been published to compare the various combinations and their efficacy.

BLT (Benzocaine, Lidocaine, Tetracaine)

BLT is a favorite compounded mixture. The percentages may vary (e.g., 20%, 7%, 7%, or 20%, 6%, 4%). With most BLT preparations, it takes 45 to 60 minutes to obtain good effect.

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