Topical Anesthetics: Composition, Absorption and Risks

Anesthetic gel is the most common and, at the same time, the least discussed item in the facial harmonization room. It enters the routine as a trivial comfort, but it has its own composition, pharmacology and risk. Most of the serious cases described with topical anesthetics involved large areas, prolonged time, occlusion and compounded products without control. This guide gathers what the professional needs to know to use these products safely. Doses, concentrations, brands and formulas are decisions for the qualified professional, following the label, the prescription and the rules of their professional council.

What is inside a topical anesthetic?

The products combine one or more local anesthetics in a base (cream, gel or ointment) that favors penetration. Among the active ingredients most often cited are lidocaine and other local anesthetics of various classes. Formulations may have:

• Low to moderate concentration, in approved commercial products;
• Higher concentration, in compounded formulas, with greater risk;
• Combinations of two or more anesthetics, which increase the effect and the chance of cumulative toxicity;
• Excipients that favor absorption, which also affects safety.

Topical anesthetic acts on the surface and the superficial layers of the skin. Part of what is applied passes into the bloodstream and adds to whatever other anesthetics used in the session have already left in the body.

Factors that increase absorption

Systemic toxicity depends on how much anesthetic reaches the blood. The main factors are:

This set of factors explains why a small area and a short time are usually safe, and a large, occluded and prolonged application is not.

Commercial and compounded products

The difference between the two groups is central.

1. Approved commercial products: they are registered with Anvisa (Brazil's health regulatory agency), have a known concentration and a label. Directions for use are standardized.
2. Compounded: they depend on a prescription and a compounding pharmacy. Weighing and concentration errors are the documented cause of serious cases.

When using compounded products, good practices include a formal prescription, a licensed pharmacy, checking the composition and concentration, clear labeling and restricting area and time. Off-label use needs justification and documentation, as covered in off-label use. Checking product registration is covered in how to check an injectable's registration with Anvisa, and the rule on other agents appears in prescribing after HOF procedures.

Who needs extra care

The medical history should identify patients in whom the absorption or elimination of the anesthetic carries a higher risk:

When in doubt, reduce area and time, or consider skipping the product. A well-taken medical history is the main safety tool.

How to use it safely in routine practice

Some measures help reduce the risk, always at the professional's discretion and following the label:

1. Define an area smaller than the whole face whenever possible, prioritizing the procedure region.
2. Define the contact time and write down the removal time.
3. Avoid occlusion that is not necessary and not provided for by the product.
4. Remove the product completely before antisepsis and the procedure.
5. Reassess the skin after removal: the gel can change color, swelling and contours.
6. Observe the patient throughout the contact time.
7. Add up all anesthetic exposures in the session, including those already present in fillers.

Topical anesthetic and other products in the session

Many fillers already contain lidocaine in the formulation. Combining it with injectable and topical anesthetic over a large area adds up doses. See hyaluronic acid with lidocaine and lidocaine allergy in facial harmonization. In patients with a history of reaction, the decision on the type of anesthesia should come before choosing the product.

How to talk with the patient

Avoid phrases like "it's just a little cream" or "there's no risk." Clear communication protects the patient and the professional.

Records and consent

Record the product and concentration, area, times, reactions and instructions. The informed consent should name the use of anesthetic and the possible adverse effects. The general framework is in patient records and documentation in HOF.

Where Harmy comes in

Common mistakes with topical anesthetics

1. Covering the whole face "just in case." More area means more absorption, and the extra comfort rarely justifies the risk.
2. Using occlusion without need. Plastic wrap speeds absorption, and should only be used if provided for and justified.
3. Leaving the product on for an indefinite time. Write down the application and removal times.
4. Accepting a compounded product without checking the formula. Concentration and combination must be known and recorded.
5. Forgetting the total dose for the session. Topical, injectable and filler with anesthetic add up their effects.

When to consider skipping topical anesthetic

In some patients, the risk-benefit balance favors skipping the product: a report of a previous reaction, relevant liver or heart disease, pregnancy, damaged skin or the need to treat a very large area. Comfort alternatives, such as cooling, careful technique, pauses and a conversation that lowers anxiety, usually help. The decision is the professional's, based on the medical history, and should be explained to the patient candidly, without suggesting that the procedure will be painless.