Compatibility and Stability of Binary Mixtures of Ketorolac Tromethamine and Tramadol Hydrochloride Injection Concentrate and Diluted Infusion Solution

ObjectiveKetorolac added to tramadol as an injection mixture convenient for clinical use has been shown to be an effective balanced analgesic regimen in alleviating moderate-to-severe pain. However, analytical confirmation of the compatibility and stability of this combination is not available. This study examined the compatibility and stability of this combination.MethodsTwo different mixtures containing ketorolac tromethamine and tramadol hydrochloride were examined: ketorolac (10 mg/mL) and tramadol (33.3 mg/mL) prepared as injection concentrate in ampoule mingled together in the ratio of one ampoule to one ampoule; diluted ketorolac (2 mg/mL) and tramadol (20 mg/mL) prepared in saline infusion solution, with or without pH adjustment. The mixtures were visually inspected for precipitation and color change. Quantitative chemical analysis was performed on days 0, 1, 3 and 7 by high-performance liquid chromatography.ResultsWhen stored at room temperature under ambient light, the ketorolac (10 mg/mL)-tramadol (33.3 mg/mL) injection concentrate and ketorolac (2 mg/mL)-tramadol (20 mg/mL) solution, without pH adjustment and adjusted to pH 5–8, were physico-chemically stable, and neither visible precipitation nor loss of concentration was found. With the ketorolac (2 mg/mL)-tramadol (20 mg/mL) solution adjusted to pH 9, however, precipitation occurred immediately, resulting in a significant loss of tramadol.ConclusionThis study suggests that a ready-to-use ketorolac-tramadol mixture, either undiluted or diluted in physiological saline solution, can be prepared, with a shelf life of at least 7 days when stored at room temperature under ambient light.