69 - Lidocaine transdermal  pp. 288-291

Lidocaine transdermal

By Maggy G. Riad

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Generic Name: lidocaine transdermal patch

Trade Name: Lidoderm Patch 5%

Manufacturer: Endo Pharmaceuticals, Chadds Ford, PA

Chemical Structure: see Figure 69.1

Description

Lidoderm is a 10 cm × 14 cm patch containing 50 mg of lidocaine per gram of adhesive material. Each patch contains a total of 700 mg of lidocaine, the only active ingredient.

Mode of activity and pharmacology

Lidocaine or lignocaine is an amide-type local anesthetic and anti-arrhythmic agent that was first synthesized and marketed in the 1940s. Lidocaine acts by blocking the fast voltage-gated Na channels in neurons by decreasing the frequency of their opening. As a consequence, depolarization and transmission of action potential in neurons is blocked, thereby decreasing both the peripheral nociceptor sensitization as well as the central nervous system hyperexcitability. In small doses lidocaine inhibits nerve discharges at aberrant or ectopic foci generated as a result of nerve injury, without interfering with normal neuronal conduction.

Bioavailability after topical administration of lidocaine via the Lidoderm patch is only 3%, which is about only 10% of its bioavailability after oral ingestion. With 70% of lidocaine being bound to plasma proteins, the blood lidocaine concentration after application of Lidoderm patch remains very low (average concentration 128 ng/mL).

Efficacy and safety of 5% lidocaine medicated plaster in comparison with pregabalin in patients with postherpetic neuralgia and diabetic polyneuropathy. Clin Drug Investig 2009;29:231–241.
Lidoderm: Endo Pharmaceuticals Inc. 2008.
Transdermal drug patches with metallic backings www.fda.gov/safety/medwatch/safetyinformation/safety.