In most cases, the level of anesthesia achieved with a topical anesthetic will be sufficient to alleviate discomfort during the injection of dermal fillers. There are basically two groups of topical agents: the ester group (cocaine, tetracaine, and benzocaine), and the amide group (lidocaine and prilocaine).
The stratum corneum is a strong barrier to the absorption of drugs through the skin. The skin should be cleaned with antiseptics before apply-
ing the topical anesthetic cream; this will allow better permeation of the topical agents. The effect might also be enhanced by rubbing a dry gauze on the surface to remove dead cells and grease. The vasodilatation that results from this rubbing of the skin may also increase the permeation of the drug. Although effective, tape stripping of the skin to remove the outer layer of dead cells and enhance penetration of the topical anesthetic is often impractical (Monash 1957).
One of the most common topical anesthetics is a eutectic mixture of 2.5 % lidocaine and 2.5 % prilocaine, which is marketed as EMLA cream. It is a nontoxic mixture whose use results in very low plasma levels. The usual dose is 1 g for each 10 cm2 of intact epidermis. The cream should be in contact with the skin for approximately 45 min to 1 h with occlusive dressing (Hallen and Uppfeldt 1982).
Cryoanesthesia is another method of inducing topical anesthesia. The simple application of ice bags may enhance the anesthetic effect. In fact, for some patients the use of ice bags alone will provide enough anesthesia. Other topical freezing agents include ethyl chloride or dichlo-rotetrafluorethane sprays, but these are unlikely to be used when the treatment involves dermal fillers.
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