Diamorphine stability in aqueous solution for subcutaneous infusion

— The influence of temperature and concentration on diamorphine stability during storage over 8 weeks has been investigated. Ampoules containing diamorphine hydrochloride in concentrations from 0·98–250 mg mL−1 have been stored at −20, 4, 21 and 37°C for 8 weeks. Their content of diamorphine, 6-monoacetylmorphine and morphine, on measurement by high performance liquid chromatography after 1, 2, 4, 6 and 8 weeks storage changed to slow degradation of diamorphine at all concentrations at temperatures of 4°C and above. This was accompanied by a corresponding increase in 6-monoacetylmorphine and morphine. There was an associated fall in pH and development of a strong odour characteristic of acetic acid. Precipitation and a white turbidity seen in solutions of 15·6 mg mL and above, appeared after 2 weeks incubation.