Premixed solutions of diamorphine in ropivacaine for epidural anaesthesia: a study on their long-term stability

Background. Local anaesthetics and opioid mixtures are commonlyused to provide anaesthesia or analgesia during the perioperativeperiod. In order to facilitate their preparation and storageit is necessary to establish the stability of such solutions. Methods. In our study, diamorphine was added to ropivacaine0.2% 200-ml polybags to give a concentration of 25 µg ml^–1and to ropivacaine 1% 50-ml syringes to give a concentrationof 45 µg ml^–1. The polybags and syringeswere stored at 40°C, 21°C and 4°C for up to 120days. Samples were taken during this period for measurementof diamorphine and ropivacaine content and pH of the solutions. Results. We found that the storage temperature and the initialconcentration influenced the rate of degradation of diamorphinein both the polybags and the syringes. In the syringes, 10%degradation of diamorphine [T (0.9)] was: 6 days at 40°C,16 days at 21°C and 30 days at 4°C. In the polybags,diamorphine T (0.9) was 6 days at 40°C, 28 days at 21°Cand 70 days at 4°C. Conclusions. It is feasible to manufacture such solutions inpharmacy aseptic units and to store them for up to 1 month forroutine use in epidural infusions. Br J Anaesth 2003; 90: 179–82