Resolution of the problems appearing in the clinical departments with relation to drug utility is a very important task for hospital pharmacists. The chief nurse of the surgery section recently asked us to examine the crystal material often appearing in the continuous infusion line of Dormicum®-Stadol® (2: 1) several hours after infusion of other medicines. The crystals were examined by high performance liquid chromatography. The retention time of the crystals was the same as that of midazolam, and the crystals were identified to be midazolam. The main cause of the formation of crystals was found to be the rise in the pH of midazolam injection due to the mixing with butorphanol injection. Moreover, the changes in ion strength and ion components in the solution affected the appearance of the crystals. Thus, midazolam should not be infused with butorphanol. If a mixture of midazolam and other medicines must be infused continuously, medical workers should check for the appearance of the crystals.
