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Synera® (lidocaine and tetracaine) consists of a thin, uniform layer of a local anesthetic formulation with an integrated, oxygen-activated heating component that is intended to enhance the delivery of the local anesthetic. The drug formulation is an emulsion in which the oil phase is a eutectic mixture of lidocaine 70 mg and tetracaine 70 mg. The eutectic mixture has a melting point below room temperature and therefore exists as a liquid oil rather than as crystals. The surface area of the entire Synera (lidocaine and tetracaine) patch is approximately 50 cm², 10 cm² of which is active.

Lidocaine is chemically designated as acetamide, 2-(diethylamino)-N-(2,6-dimethylphenyl), has an octanol:water partition ratio of 182 at pH 7.3 and has the following structure:

Tetracaine is chemically designated as 2-(dimethylamino)ethyl p-(butylamino)benzoate, has an octanol:water partition ratio of 5370 at pH 7.3 and has the following structure:

Each Synera patch contains lidocaine 70 mg and tetracaine 70 mg in a eutectic mixture. The Synera (lidocaine and tetracaine) formulation also contains the following inactive ingredients: polyvinyl alcohol, sorbitan monopalmitate, water, methylparaben and propylparaben.

The Synera (lidocaine and tetracaine) heating component generates a mild warming that is intended to enhance the delivery of the local anesthetic. Synera (lidocaine and tetracaine) begins to heat once the patch is removed from the pouch and is exposed to oxygen in the air. Although the patch may increase skin temperature by up to approximately 5ºC, maximum skin temperature will not exceed 40ºC. The heating component is composed of iron powder, activated carbon, sodium chloride, wood flour, water and filter paper.

Last reviewed on RxList: 1/23/2009
This monograph has been modified to include the generic and brand name in many instances.