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The formulation may be stored for 5 days in the refrigerator.

The stability of diamorphine (0.02 mg/ml as the hydrochloride) in 250 ml bupivacaine hydrochloride (0.15% wt/vol infusion) was studied by high pressure liquid chromatography at temperatures in the range 7 to 45 degrees C. Diamorphine hydrochloride was degraded by approximately 0.13% per day at 7 degrees C. No bupivacaine hydrochloride degradation was detectable during the study. The storage life of the combination at 7 degrees C, based on the lower 95% confidence limit of the time to 5% diamorphine hydrochloride degradation, was 14 days. The stability at 25 degrees C was adequate to allow transport and administration over 24 h at ambient temperature. Stability was also maintained for at least 24 hr at 32 and 45 degrees C. Infusion of the mixture with an ambulatory infusion pump which uses a standard polyvinyl infusion bag is therefore possible. A study of its compatibility with different infusion pump medication reservoirs was not undertaken. The drugs were also stable on frozen storage at -18 degrees C for up to 6 months.

The efficacy of various common antimicrobial preservatives was tested in eye drop formulations containing the cephalosporin antibiotics cefuroxime and ceftazidime. The British Pharmacopoeia test for the efficacy of antimicrobial preservatives was used and the formulations were challenged with Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. The survival of organisms was monitored over 14 days. Cefuroxime sodium, 50 mg/ml, was studied in simple aqueous solution, and dissolved in an artificial tear formulation, Sno Tears (Smith and Nephew Pharmaceuticals), which contains benzalkonium chloride 0.004% w/v. Ceftazidime (50 mg/ml) was also studied in these two vehicles and, in addition, in a phenylmercuric acetate solution (0.002% w/v) and chlorhexidine acetate (0.02% w/v). Cefuroxime and ceftazidime contributed little, in the short-term, towards a microbicidal preservative effect in the unpreserved aqueous formulations, even against organisms for which they were active. Cefuroxime was adequately preserved in a vehicle of Sno Tears, which contains benzalkonium chloride as the antimicrobial preservative. Ceftazidime was less well preserved in this vehicle, but it was superior to phenylmercuric acetate (0.002% w/v) or chlorhexidine acetate (0.02% w/v).