Preparation, Characterization, and In Vitro Evaluation of Cream & Gel Formulations Containing Lidocaine and Tetracaine

There are multiple different topical anesthetic options available to minimize the pain associated with cosmetic dermatologic procedures. These options are used either alone or in combination and the most used dermal analgesics are lidocaine, tetracaine, prilocaine, or their combinations. EMLA® cream is a local anesthetic that contains lidocaine and prilocaine combination and can be applied to the skin to help suppressing the pain of needle procedures, but it requires occlusion and the length of time for the medication to stay on the skin depends on the type of procedure. It is usually applied at least 1-2 hours before minor skin procedures. The object of this study was to develop topical cream and gel formulations of lidocaine-tetracaine (LT) combination with a suitable consistency to maintain an effective pain alleviation with a faster onset of action which may be an alternative to EMLA® in superficial operations. Two different formulations of LT; a water-in-oil (w/o) emulsion and an emul gel thickened with Carbomer 974 were manufactured. pH levels of emulgel formulations were ranged between 7.2-7.7 at t 0 , and 8.2-8.9 at t 30 , respectively. The w/o cream and emulgel formulations showed shear thinning thixotropic behavior at t 0 and t 30 . The morphological properties have been analyzed with a texture analyzer, and properties such as hardness, cohesiveness, and elasticity were calculated. The yield percentage of lidocaine was 65-100%, and tetracaine was 45-100% in emulgels, and 39-79% and 47-67% in creams. In vitro studies showed that LT release was faster in emulgel formulations, and tetracaine release had a longer duration in all formulations. In conclusion, cream and emulgel formulations of LT combination with a suitable consistency, pH level and longer duration of action have been manufactured and evaluated by means of in vitro tests.