title: Stability of premixed syringes of diamorphine and hyperbaric bupivacaine.
abstract: BACKGROUND
  It is common clinical practice to add diamorphine to heavy bupivacaine when performing spinal anaesthesia for either obstetric or general surgical procedures. If pre-filled syringes were available potential problems arising due to the wrong mixture being administered could be reduced, whilst also providing greater assurances of sterility and accuracy of dosage. It is therefore necessary to establish whether diamorphine 100 microg/mL is stable in solution with 0.5% hyperbaric bupivacaine, to allow production of pre-filled syringes for use in spinal anaesthesia.
  
  
  METHODS
  Diamorphine hydrochloride was dissolved in water for injection, and added to hyperbaric bupivacaine then stored in 5-mL plastic syringes. Eleven syringes were stored at 40 degrees C/75% relative humidity, 25 degrees C/60% relative humidity and 7 degrees C for 90 days. Samples were taken at five time points for measurement of diamorphine and bupivacaine concentrations using high performance liquid chromatography.
  
  
  RESULTS
  Diamorphine concentrations fell over the study period. No significant changes were observed the bupivacaine content of the samples. There was 10% degradation of diamorphine after 4 days at 40 degrees C, after 7 days at 25 degrees C, and after 26 days at 7 degrees C.
  
  
  CONCLUSIONS
  Diamorphine is stable in hyperbaric bupivacaine at 7 degrees C for long enough to allow preparation of pre-filled syringes in advance (by hospital pharmacy aseptic units) for use in spinal anaesthesia.
authors.affiliation: Department of Anaesthesia and Pharmacy, Broomfield Hospital, Chelmsford and Quality Control North West, Stepping Hill Hospital, Stockport, UK. sonia@sjhudson.freeserve.co.uk
authors.forename: S J
authors.initials: SJ
authors.lastname: Hudson
authors.forename: M F
authors.initials: MF
authors.lastname: Jones
authors.forename: S
authors.initials: S
authors.lastname: Nolan
authors.forename: H
authors.initials: H
authors.lastname: Ellis
authors.forename: R
authors.initials: R
authors.lastname: Duncombe
authors.forename: J M
authors.initials: JM
authors.lastname: Alexander-Williams
mesh_terms: D000701:Analgesics, Opioid; D000775:Anesthesia, Spinal; D019162:Anesthetics, Combined; D000779:Anesthetics, Local; D002045:Bupivacaine; D002851:Chromatography, High Pressure Liquid; D004355:Drug Stability; D004356:Drug Storage; D003932:Heroin; D013594:Syringes; D013696:Temperature
chemical_list: D000701:Analgesics, Opioid; D019162:Anesthetics, Combined; D000779:Anesthetics, Local; D003932:Heroin; D002045:Bupivacaine