Stability studies on compounded topical local anesthetic preparations

Abstract

Objective: This study was to investigate the long-time stability (60 days) of local anesthetic preparations containing single active pharmaceutical ingredient (API), namely benzocaine, lidocaine HC1, and tetracaine HC1 in VersaPro Cream Base, Medisca, and stored at room temperature (25(degrees)C) and under refrigeration (4(degrees)C). Methods: Homogenous creams containing known concentrations of benzocaine, lidocaine HC1, and tetracaine HC1 were prepared in our lab and the anesthetic content was assayed using reverse-phase high-pressure liquid chromatography (HPLC). The stationary phase included Zorbax Eclipse Plus columns (CI8 and 4.6 null 150 mm, 3.5 particle size, 95A pore size, pH range 2-9; Agilent Technologies, Santa Clara, CA), while the mobile phase consisted of water and acetonitrile as organic modifier in concentrations appropriate for each API. The column temperature was maintained at 40(degrees)C. The absorption wavelengths for quantification were 225, 320 and 280 nm for lidocaine, HC1, tetracaine HC1, and benzocaine, respectively. The creams were then stored at room temperature and under refrigeration. The samples were assayed freshly after preparation and then after 30 and 60 days. Results: An appropriate standard curve was constructed for each individual local anesthetic. The standard curve contained four relevant concentration levels and five repetitions of each level. The potency for lidocaine HC1, tetracaine HC1, and benzocaine stored at room temperature was found to be 96%, 98.5%, and 99% of added concentration, respectively. The refrigerated samples did not show any improvement in potency. Conclusion: Evidences conclusively prove that all the investigated APIs, namely benzocaine, lidocaine HC1, and tetracaine HC1, conserve their potency in the VersaPro Cream Base stored at room temperature for 60 days. Refrigeration of the preparations is neither necessary nor helpful in preserving their potency.