Topical Anesthetics
EMLA = eutectic mixture of local anesthetic (combination of lidocaine & prilocaine)
- Pregnancy Category B
- Most effective topical anesthetic
- Applied under occlusion with a 60-min application period
- Block nerve conduction via reversible inhibition of sodium ion influx preventing depolarization
- Smaller diameter nerves are most susceptible (C & Aδ fibers – pain & temperature) whereas large nerves are more resistant (Aβ fibers -pressure)
- Most resistant nerves are proprioception & motor nerves
- Amount of EMLA systemically absorbed is directly related to the surface area of application as well as duration of contact with skin, specifically, longer duration & occlusion increase EMLA penetration & efficacy
- Metabolism via hepatic microsomal CYP enzymes
FDA
- Topical analgesia prior to surgery, laser, debridement of leg ulcers
Off-label
- Mucosal analgesia, Pruritus, Postherpetic neuralgia, Hyperhidrosis
Absolute
- Hypersensitivity, methemoglobinemia
Relative
- Hypersensitivity to anesthetics other than lidocaine/prilocaine, Mucosal application, Application on broken skin, G6PD deficiency, age <1 month, Pregnancy, significant cardiac or hepatic impairment
- Methemoglobinemia (prilocaine)
- Toxicity (very rare)
- Local reactions: stinging, burning, pruritus, blanching, erythema, allergic contact dermatitis
Medications that may increase risk of methemoglobinemia with EMLA
- Acetaminophen, Aminosalicylic acid, Phenobarbital, Phenytoin, Antimalarials, Nitrates, Sulfonamides
Methemoglobinemia:
Risk due to prilocaine component of eutectic mixture of local anesthetic (EMLA), higher with:
- Patients with congenital or acquired methemoglobinemia
- Patients on medications that may increase the risk of methemoglobinemia
- G6PD deficiency
- Patients younger than 1 year of age
Management of methemoglobinemia (acute)
- Plasmapheresis, methylene blue
Other topical anesthetics
- Lidocaine (Lidocaine 4% cream “LMX4”, lidocaine 5% cream ‘LMX5”), Benzocaine (higher risk of allergic reactions)