Stability of Tetracycline Hydrochloride in Miracle Mouthwash Formulations Containing Diphenhydramine and Dexamethasone Elixir

Abstract

Objectives: To assess the solubility and stability of tetracycline in compounded miracle mouthwash solutions over time, and at different temperatures (room temperature versus refrigerated) and pH (unaltered versus pH 7). Methods: Miracle mouthwash (MMW) solutions were compounded using tetracycline HCl capsules and 1:1 pseudo-dexamethasone elixir and diphenhydramine. High-performance liquid chromatography (HPLC) was used to measure the tetracycline concentrations in the MMW samples tested. Data on tetracycline crystal composition over time were also collected using powder x-ray diffraction, differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). Results: For the tetracycline MMW solutions stored at room temperature, only 16% of the original tetracycline remained in solution after 24 hours, stabilizing at 65-81 mcg/mL on day 5 then decreasing further down to 45 mcg/mL by day 15. Similar results were obtained for the refrigerated tetracycline MMW solution (11% of original concentration after 5 days, with a decrease from 31-54 mcg/mL on day 5 to 22 mcg/mL on day 15). Tetracycline concentrations appeared to undergo a steeper decline in MMW solutions of pH 7 than in unadjusted MMW solutions (pH 4.68). All MMW samples exhibited a conversion from tetracycline HCl to tetracycline hexahydrate. Conclusions: Tetracycline solubility decreases rapidity in MMW within 24 hours of compounding regardless of temperature. MMW solutions at pH 7 may have further reduced solubility. Stability decreases at a stable rate from tetracycline HCl to tetracycline hexahydrate.