Several methods are available to ease pain or discomfort for minor dermatologic procedures [28
]. Application of the lidocaine/tetracaine medicated patch or peel to the skin 30 or 60 minutes before procedures may be an effective and safe means of anesthesia. Moreover, both the patch and peel formulation types provide convenient, noninvasive and painless means of application, with a rapid onset, minimal adverse effects, without the need for occlusion and easy removal [19
]. Many clinical trials confirmed these potential advantages [7
]. However, a comprehensive literature analysis has not yet performed to test the hypothesis that the lidocaine/tetracaine medicated patch or peel is indeed an effective and safe method for reducing procedural pain. The present systemic review addressed the efficacy by comparing the patch or peel to placebo. Ten randomized, controlled trials were combined, and the data were statistically homogenous so a fixed effects model was used. Thus, we were able to draw a conclusion that the lidocaine/tetracaine medicated patch or peel was consistently and significantly more efficacious than placebo, based on subject-reported pain intensity, using the VAS scores.
A patch delivery system provides a specific amount of drug to a clearly distinct dermal area and is easier to apply and remove than the peel formula. Half the trials were with a patch formula, and the other half examined peel type applications. A transdermal patch included an oxygen-activated heating pad containing lidocaine and tetracaine [7
]. This newly-developed drug delivery system uses controlled heat to enhance the delivery of local anesthetics through the skin. But the system was not found superior to the peel type application in this review. There was not much difference in efficacy and safety between subgroups of the lidocaine/tetracaine medicated patch and peel for dermal anesthesia over intact skin. Patches were administered for 20 minutes in 2 trials and for 30 minutes in 2 trials and for 39 minutes in 1 trial. For the peel type applications, they were administered for 30 minutes in 2 trials and for 60 minutes in 3 trials. Similar outcomes of RR and NNT might be attributed to the fact that the duration time of application was not considered in this review. It will be necessary to determine the impact of a heating component on the onset time with RCTs.
Adverse effects of the lidocaine/tetracaine medicated patch and peel were limited to transient mild erythema, blister, burning sensation, itching and edema. Even though the adverse effects were considered to be moderate in severity, they were resolved without intervention. Patch type formulas showed slightly more erythema and edema than placebo due to the vasodilating action of tetracaine and local heating system of the patch [9
]. However, the difference in frequency was small so that the incidence of adverse effects of the medicated patch and peel was not significantly different from placebo, even when comparing 4 trials with the patch-type application. The potential for systemic absorption of tetracaine and lidocaine through intact skin is insignificant because blood concentrations of tetracaine and lidocaine were reported to be below the lower limit of quantitation [8
]. The use of a medicated patch and peel was judged safe in this review.
There is a limitation of this study. Although we tried to minimize publication bias during arranging the process of review, there exist possible sources of error. Publication bias (Egger's regression method, P < 0.01), the tendency of studies with positive results to be accepted as well as negative reports to be rejected, may alter the study outcome.
We concluded that the lidocaine/tetracaine medicated patch and peel were highly efficacious and safe in reducing local pain when applied 60 minutes prior to minor dermal procedures. Indeed, our results indicated that the patch and peel formula provided several potential clinical advantages such as minimal adverse effects and adequate dermal anesthesia in both adult and pediatric patients. Further trials are warranted to assess the effects of a heating drug delivery system on topical dermal anesthesia, prolongation of duration and reduction of the time of onset. Further, well-designed clinical trials are needed to compare the formulas with EMLA, liposome-encapsulated lidocaine or tetracaine, and BLT: triple anesthetic gel.