Chemical Stability of Morphine, Ropivacaine, and Ziconotide in Combination for Intrathecal Analgesia

Pain is the most feared symptom amongst individuals living with cancer. In 15% to 20% of patients, conventional analgesic therapy either fails to relieve pain or induces adverse effects. Intrathecal drug delivery systems may present an effective alternative for pain management. The Cancerology Center Paul Papin protocol includes an admixture of morphine, ropivacaine, and ziconotide in intrathecal preparations. These drugs are administered by a fully implantable or an external pump. Syringes or polyolefin infusion bags are prepared for refill just before use. Few centers in France use the method of intrathecal analgesia. Therefore, for those patients receiving intrathecal preparations, each filling requires that the patients be transported from their local hospital (or their home) to a referral center where the patients are monitored. They sometimes must travel up to a hundred kilometers to have a pump filled. The preparation and the analytical control of the mixture are carried out only by those centers meeting the proper criteria, which includes the proper equipment. To spare the patient this travel, a peripheral center may be subcontracted to manage the patient's pump refill. No data are available concerning the chemical stability of admixtures in syringes or polyolefin infusion bags. The aim of this study was to evaluate, with a new analytical method using ultra high-performance liquid chromatography, the chemical stability of these admixtures in syringes or in polyolefin infusion bags. Ziconotide 1 µg/mL was combined with ropivacaine (7.5 mg/mL) and morphine (3.5 mg/mL) in syringes at 5°C, 21°C, and 31°C, and in polyolefin infusion bags at 21°C. Assays were performed using ultra high-pressure liquid chromatography. In syringes stored at 21°C and 31°C, concentrations after 6 hours were not in the acceptable criterion of 10% variability. When syringes were stored at 5°C, the residual concentration of ziconotide after 3 days was 100.5% +/- 2.6% [92.7% to 108.4%]. In polyolefin infusion bags, the residual concentration of ziconotide after 14 days was 96.9% +/- 2.2% [90.1% to 103.6%]. This study demonstrates the chemical stability of this admixture in syringes stored at 5°C for 3 days and in polyolefin plastibags stored at 21°C for 14 days.