Stability of Extemporaneously Prepared Amitriptyline Hydrochloride Topical Preparations for the Treatment of Neuropathic Pain

Abstract

Objective: The aim of this study was to investigate the physicochemical and microbiological stability of extemporaneous amitriptyline hydrochloride (AMH) topical preparations for the treatment of neuropathic pain. Materials and Methods: AMH tablets were triturated to produce fine powders with a mortar and pestle. These powders were levigated and separately incorporated into four compounding bases: hydrophilic petrolatum USP, anionic cream, cold cream USP, and pluronic lecithin organogel (PLO) having the concentration of 2%w/w AMH. Results: In the in vitro release study, the most significant amount of AMH was released from the PLO, followed by cold cream, anionic cream and hydrophilic petrolatum, respectively; therefore, the compounded AMH in cold cream and AMH in PLO were selected for the evaluation of the in vitro permeation and product stability. The permeation of AMH from PLO across human epidermal membrane was significantly greater than that from the cold cream. Product stability was characterized as having no remarkable change in color or texture and AMH remaining in the range of 90–110% of the initial concentration quantified by high-performance liquid chromatography. Compounded AMH in cold cream was stable at 2–8 °C and 30 °C for 60 days, and 40 °C for 30 days, whereas compounded AMH in PLO was stable at 30 °C and 40 °C for 14 days. There was no visible microbial growth in any of the samples. Conclusion: Taken together with the in vitro permeation and product stability studies, the present study suggests that AMH in cold cream could be prepared and used as extemporaneous topical preparations with a beyond-use date of 60 days when kept at 2–8 °C and 30 °C.