Topical Anesthetic Agents

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 burns to decrease the sensitivity of nerve endings in the affected area.

The first topical anesthetic agent was TAC, which is a combination of tetra-caine, 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 generally preferred over TAC as analgesia for skin that is not intact because LET has a superior safety record and is more cost-effective than TAC.

Perhaps the most well known topical anesthetic for intact skin is EMLA. EMLA is commonly used to anesthetize skin before IM injections, venipuncture, and simple skin procedures such as curettage or biopsy. EMLA is most effective if administered 90 minutes before the procedure.

ELA-Max (4% Liposomal Lidocaine) is another topical anesthetic for intact skin that works faster than EMLA. EL-Max is an over-the-counter medication that uses the liposomal delivery system. Liposomes are tiny lipid (fat) balls that deliver moisture to the skin. Because of their small molecular size, they are able to penetrate the cell wall reasonably well and can be used to deliver medications.

Other topical anesthetics can be delivered using iontophoresis—a therapy that uses a local electric current to introduce the ions of a medicine into the tissues—and anesthetic patch.

Topical Anesthetic Agents

TAC (0.5% tetracaine, 1:2,000 epinephrine, and 11.8% cocaine)

2 to 5 mL (1 mL per cm of laceration) applied to wound with cotton or gauze for 10 to 30 minutes; Onset: effective 10 to 30 minutes after application; Duration: not established; May be as effective as lidocaine for lacerations on face and scalp; Rare severe toxicity, including seizures and sudden cardiac death.

LET (4% lidocaine, 1:2,000 epinephrine, and 0.5% tetracaine)

1 to 3 mL directly applied to wound for 15 to 30 minutes; Onset: 20 to 30 minutes Duration: not established; Similar to TAC for face and scalp lacerations; less effective on extremities; No severe adverse effects reported

EMLA (2.5% lidocaine and 2.5% prilocaine)

Thick layer (1 to 2 g per 10 cm2) applied to intact skin with covering patch of Tegaderm; Onset: must be left on for 1 to 2 hours Duration: 0.5 to 2 hours; Variable, depending on duration of application; Contact dermatitis, methemoglobinemia (very rare)

Iontophoresis

Small current applied to lidocaine-soaked sponges on intact skin; Onset: 10 minutes; Duration: 10 to 20 minutes; Good for small procedures, depth of anesthesia greater than EMLA; Stinging sensation; may burn skin if high current

Other Local Anesthetic Agents

Procaine (Novocaine)

Short-acting (1/2 to 1 hour)—ester, first synthetic local anesthetic, relatively safe due to rapid metabolism in the plasma, fast onset-short duration, not good for topical anesthesia

Cocaine

Ester, only local anesthetic that is a vasoconstrictor, only local anesthetic that produces euphoria, used by ENTs for surgical procedures because it reduces pain and controls bleeding.

Tetracaine (Pontocaine)

Long-acting—ester—used for spinal anesthesia and topical

Bupivicaine

Long-acting—amide—can be cardiotoxic at high concentrations, used for infiltration, epidural and nerve blocks.

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