Stability of epinephrine hydrochloride in an extemporaneously compounded topical anesthetic solution of lidocaine, racepinephrine, and tetracaine

The stability of lidocaine, epinephrine (as racepinephrine, or racemic epinephrine), and tetracaine (LET) in a topical anesthetic solution under various conditions was studied. The LET solution was prepared by mixing together 100 mL of 20% lidocaine hydrochloride, 50 mL of 2.25% racepinephrine (as the hydrochloride salt), 125 mL of 2% tetracaine hydrochloride, 315 mg of sodium metabisulfite, and 225 mL of water. The solution was stored in three amber glass and two clear glass bottles. One amber container and one clear container were stored at 35 °C, one amber and one clear container were stored at room temperature (~18 °C), and the third amber container was stored at 4 °C. Except for the refrigerated container, each bottle was subjected to continuous room light. Each of the five solutions was sampled at 0, 1, 2, 3, 4, 8, 16, and 26 weeks for visual inspection and high-performance liquid chromatography (HPLC). The HPLC assay was shown to be stability indicating for epinephrine only. All the drugs in the LET solution had no more than a 5% reduction from initial concentration, according to the assay, when stored for 4 weeks in amber or glass containers at 4 or 18 °C and when stored for 26 weeks in amber containers at 4 °C. Solution stored in clear containers discolored more quickly than solution stored in amber containers. Epinephrine in an extemporaneously prepared LET solution was stable in amber glass bottles for 4 weeks at 18 °C and for 26 weeks at 4 °C.