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 deliverysystem. 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.
CHAPTER 15 Nervous System Drugs^279
Topical Anesthetic Agents
TAC (0.5% tetracaine, 1:2,000 2 to 5 mL (1 mL per cm of laceration) applied to
epinephrine, and 11.8% cocaine) 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 1 to 3 mL directly applied to wound for 15 to
epinephrine, and 0.5% tetracaine) 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 Thick layer (1 to 2 g per 10 cm^2 ) applied to intact
2.5% prilocaine) 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