Anesthesia, Topical

Anesthesia, Topical

Author: Mary L Windle, PharmD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy, Pharmacy Editor, eMedicine.com, IncContributor Information and DisclosuresUpdated: Jun 4, 2008

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ReferencesOverview

Many options to deliver anesthesia have developed over the last several decades. Administration of topical anesthetics to control pain associated with procedures such as laceration repair may avoid the need for infiltrative local anesthesia injections and associated pain from the injections. Topical anesthesia also avoids the risk of wound margin distortion that exists with infiltrative injection administration. Many dosage forms exist (eg, gels, sprays, creams, ointments, patches) and provide the clinician with precise options for application under various circumstances.Mechanism of action

Topical anesthetics reversibly block nerve conduction near their site of administration, thereby producing temporary loss of sensation in a limited area. Nerve impulse conduction is blocked by decreasing nerve cell membrane permeability to sodium ions, possibly by competing with calcium-binding sites that control sodium permeability. This change in permeability results in decreased depolarization and an increased excitability threshold that, ultimately, prevents the nerve action potential from forming.1,2,3 AbsorptionSkin absorption is highly variable. Most anesthetic agents exist as solids and are only superficially absorbed through intact skin. Eutectic mixtures result in liquids that melt at lower temperatures than their single components. This permits higher concentrations of anesthetics, which results in superior dermal anesthesia for intact skin. Other methods of increasing skin penetration include liposomal preparations, iontophoresis, and transdermal patches.1,3

Indications

Topical anesthetics are used for various skin and mucous membrane conditions, including (but not limited to) pruritus and pain due to minor burns, skin eruptions (eg, varicella, sunburn, poison ivy, insect bites), and local analgesia on intact skin. With the exception of lidocaine-prilocaine as a eutectic mixture (EMLA), topical anesthetics are poorly absorbed through intact skin. Because of variation in systemic absorption and toxicity, the ideal choice of topical anesthetic and particular concentration depends on the intended use. EMLA has also been applied to children to minimize discomfort prior to injections or to starting an intravenous line.2,3 Dosage guidelines and administrative techniques

Apply the cream, ointment, or solution to the chosen area in incremental amounts.

The total dose for a topical anesthetic is smaller than that used for subcutaneous infiltration.

EMLA cream does not require an occlusive dressing (eg, DuoDERM, Tegaderm, Saran Wrap); however, when an occlusive dressing is applied, absorption is improved and time of onset is decreased.2,3 Viscous lidocaine may be used alone or in a compounded mixture as a mouthwash (ie, swish and expectorate).3 Iontophoresis has been used to improve the effects of topical anesthesia; however, the equipment is expensive and bulky, and some patients experience discomfort from the mild electrical sensation.1,3 Sequential layered application of topical lidocaine with epinephrine (TLE) has been described for small facial or scalp wounds. One-hundred patients were enrolled in a randomized controlled trial, with 50 in each group. The study group received TLE using a unique method of "sequential layered application." The control group received 2% lidocaine infiltration anesthesia. Patients rated the pain from the application of anesthesia and from suturing, using a zero-to-ten visual analog pain scale. Follow-up interviews were conducted to assess for complications and to rate patients' wound repair experience. Patients in the study group reported significantly less pain from TLE application, with 66% reporting no pain vs 0% reporting no pain from the infiltration in the control group (P