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

BACKGROUND

Local anaesthetics and opioid mixtures are commonly used to provide anaesthesia or analgesia during the perioperative period. In order to facilitate their preparation and storage it is necessary to establish the stability of such solutions.

METHODS

In our study, diamorphine was added to ropivacaine 0.2% 200-ml polybags to give a concentration of 25 micro g ml(-1) and to ropivacaine 1% 50-ml syringes to give a concentration of 45 micro g ml(-1). The polybags and syringes were stored at 40 degrees C, 21 degrees C and 4 degrees C for up to 120 days. Samples were taken during this period for measurement of diamorphine and ropivacaine content and pH of the solutions.

RESULTS

We found that the storage temperature and the initial concentration influenced the rate of degradation of diamorphine in both the polybags and the syringes. In the syringes, 10% degradation of diamorphine [T (0.9)] was: 6 days at 40 degrees C, 16 days at 21 degrees C and 30 days at 4 degrees C. In the polybags, diamorphine T (0.9) was 6 days at 40 degrees C, 28 days at 21 degrees C and 70 days at 4 degrees C.

CONCLUSIONS

It is feasible to manufacture such solutions in pharmacy aseptic units and to store them for up to 1 month for routine use in epidural infusions.