Intra-articular injection composed of steroid, iohexol and local anaesthetic: is it stable?

The aim of this study is to determine the chemical stability of a suspension of steroid, radiographic contrast material and local anaesthetic. Image-guided steroid injection using a contrast material is widely used for several musculoskeletal conditions. Manufacturers of these agents do not advise mixture in a single syringe, as the chemical stability is unknown. They suggest that, if required, these agents should be injected separately. However, the agents will be mixed together when injected into a contained space within the body. It would seem unethical to continue this in clinical practice until the stability of such a mixture is established. High-performance liquid chromatographic (HPLC) analysis was used to assess the stability of combinations of steroids (triamcinolone and methylprednisolone) and Omnipaque (iohexol). Further analysis was also performed to test the stability of adding local anaesthetics (lidocaine and bupivacaine) to these mixtures. The results demonstrated that all combinations were stable when mixed together. In conclusion, these results support the continued safe use of these products in combination in clinical practice.