Effect of morphine sulfate concentration on flow rate in an implantable reservoir pump

The effect of morphine sulfate concentration on flow rate in an implantable pump was studied. Solutions containing morphine sulfate 5 mg/3 ml, 10 mg/3 ml, 20 mg/3 ml, and 200 mg/3 ml were prepared from morphine sulfate powder; a solution containing morphine sulfate 20 mg/3 ml with bupivacaine hydrochloride 0.125% was also prepared. Sterile water was used for preparing the morphine solutions and as the control solution. A model 400 Infusaid pump was filled with 50 ml of the drug solution, placed in a water bath at 37 degrees C, and allowed to equilibrate for three hours. Samples of each concentration of morphine solution and control solution were then collected in an analytical graduate over 20-hour periods. Between each collection period, the pump was flushed twice with sterile water. Five samples of each morphine solution and control solution were collected. The osmolality of one sample of each solution was determined to assess drug concentration indirectly; morphine sulfate concentrations were not actually measured. Actual solution volumes collected during the 20-hour collection periods were corrected to 24 hours to allow comparison with the pump's preset daily flow rate. Collection volumes and calculated daily flow rates decreased with increasing morphine sulfate concentrations and solution osmolalities; a significant positive correlation between osmolality and assumed drug concentration was found. The flow rate of the solution containing morphine 200 mg/3 ml was approximately equal to the pump's stated flow rate; flow rates for all other solutions were higher than the stated flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)