What is transdermal anesthesia, specifically the brand-name medication Numby (lidocaine)?

From the Guidelines

Numby is a topical anesthetic cream containing lidocaine and prilocaine that provides transdermal anesthesia for minor procedures, and its use is recommended as a first-line method of anesthesia for nonablative laser treatments and minor dermatologic procedures, according to the guidelines for the use of local anesthesia in office-based dermatologic surgery 1. The cream typically contains 2.5% lidocaine and 2.5% prilocaine in an oil-in-water emulsion.

• For effective use, apply a thick layer of Numby cream to intact skin and cover with an occlusive dressing for 30-60 minutes before the procedure.
• The cream works best when applied at least 1 hour before needle procedures, minor skin surgeries, or laser treatments.
• The medication works by blocking sodium channels in nerve membranes, preventing the generation and conduction of pain signals.
• Common application sites include the antecubital fossa for blood draws, the dorsum of hands, and facial areas for cosmetic procedures.
• Side effects are generally mild and include temporary skin blanching, redness, or slight swelling at the application site.
• Numby should not be used on mucous membranes, open wounds, or in patients with known allergies to amide anesthetics.
• The anesthetic effect typically lasts 1-2 hours after removal of the cream. It is also important to note that noncocaine formulations, such as Numby, are preferred over cocaine formulations due to the increased cost and potential for adverse events associated with cocaine 1.
• Additionally, the use of topical anesthetic agents, such as Numby, can help to lessen the pain of injection and reduce the dose of infiltration anesthesia needed for larger procedures 1.
• However, it is essential to follow the recommended guidelines for the use of local anesthesia in office-based dermatologic surgery to minimize the risk of adverse events 1.
• The most recent guidelines, such as those published in 2021, provide recommendations for the safe use of intravenous lidocaine, but these are not directly applicable to the use of topical anesthetics like Numby 1.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Transdermal Anesthesia

• Transdermal anesthesia, also known as "Numby", is a method of administering anesthesia through the skin to reduce pain sensation.
• The efficacy of transdermal anesthesia can be influenced by various factors, including the type of anesthetic agent used, the concentration of the agent, and the duration of application 2, 3.
• Studies have shown that lidocaine and prilocaine are effective topical anesthetic agents, with lidocaine alone and a lidocaine and prilocaine mixture showing a stronger skin sensitivity reduction compared to benzocaine 2.
• The site of application is also an important factor, with palatal mucosa being more resistant to the effects of topical anesthetics than other intraoral sites 3.

Topical Anesthetic Agents

• Lidocaine is a commonly used topical anesthetic agent, effective at concentrations between 5% and 20% 3.
• The combination of 2.5% lidocaine and 2.5% prilocaine has been shown to be a reliable agent, although it is not licensed for intraoral use 3.
• Benzocaine is effective when used alone at a concentration of 20% and when combined at a dose of 15% with 1.7% amethocaine 3.
• Other topical anesthetic agents, such as EMLA cream, have also been shown to be effective in reducing pain sensation 4, 5.

Advantages of Transdermal Anesthesia

• Transdermal anesthesia offers several advantages over systemic analgesic administration, including a lower risk of addiction and minimal systemic effects 5.
• Transdermal and topical routes of administration can provide long-lasting analgesia and are convenient for patients who are unable to take drugs orally 5.
• Topically administered drugs can act locally in tissues, reducing the risk of adverse effects and providing targeted pain relief 5.