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An EMLA patch contains a mixture of two local anesthetics, lidocaine and prilocaine. They are used to cause numbness of the skin in areas where pain is expected, such as before a needle is used for taking blood or injecting some vaccines. The patch is applied some time before the procedure and minimizes pain, although some pressure may still be felt.
The EMLA patch's area of application and its duration on the skin differs according to age, and will be advised by the prescribing doctor. The skin should be cleaned and dried before application. Usually, the patch is applied at least an hour before the procedure to allow absorption of the lidocaine and prilocaine into the skin so that their anesthetizing property can take effect. In adults, the patch may be left on for up to five hours, and more than one patch may be applied, but this is not recommended for small children.
Pain is caused by stimulation of the nerve endings in the skin, which sets off a process involving sodium, ultimately sending an electrical pain signal to the brain. The EMLA patch stops this by preventing the flow of sodium and the electrical signal to the brain, thus stopping the feeling of pain. The onset of this mechanism takes a bit of time. For this reason, the EMLA patch needs to be applied a sufficient amount of time before the painful procedure is set to occur. To ensure that the patch is not left on longer than recommended, it is advised that the time of application be written on the patch, in permanent marker.
EMLA patches have been used prior to vaccinations. This should only be done under medical supervision, as some vaccines may not be given after the use of EMLA patches. The patch should also not be applied to any open wounds, broken skin, or mucous membranes. Lidocaine/prilocaine may interact or have additive side effects with other medications, so these should be discussed with the prescribing doctor before the EMLA patch is used. Concomitant diseases or conditions should also be discussed.
As with any medication, the EMLA patch may have adverse effects. The most common of these are mild local skin problems, including redness, itchiness or stinging at the site of application. These should clear up spontaneously. If they don't, or more severe or systemic symptoms are experienced, medical help should be sought immediately.