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ANESTHETIC PHARMACOLOGY

The Stability of a Ketamine-Morphine Solution

Roger Schmid, MD^*, Gideon Koren, MD, FACMT, FRCPC, Julia Klein, MS, and Joel Katz, PhD^*

*Department of Anesthesia and Pain Management, Toronto General Hospital; Departments of Pediatrics, Pharmacology, Pharmacy, Medicine, and Medical Genetics, University of Toronto and The Research Institute, Division of Clinical Pharmacology/Toxicology, Hospital for Sick Children; Departments of Anesthesia and Public Health Sciences, University of Toronto, and Department of Anesthesia and Pain Management, Mount Sinai Hospital, Toronto, Canada

Address correspondence and reprint requests to Joel Katz, Department of Anesthesia and Pain Management, Toronto General Hospital, 200 Elizabeth St., EN 3-440, Toronto, ON, Canada M5G 2C4. Address e-mail to jkatz{at}uhnres.utoronto.ca

Recent advances in acute pain mechanisms and management have implicated the N-methyl D-aspartate receptor-ion channel complex in the development of postoperative hyperalgesia and acute opioid tolerance. N-methyl D-aspartate receptor antagonists such as ketamine have been used increasingly in clinical studies in an effort to minimize acute postoperative pain and reduce opioid requirements. A mixture of ketamine and an opioid administered in the same solution and syringe would be a practical and useful technique for postoperative epidural analgesia, continuous IV infusion, or patient-controlled IV analgesia. We investigated the stability of a morphine sulfate and racemic ketamine solution in saline at pH 5.5–7.5 over a period of 4 days. Our study demonstrates that the ketamine-morphine mixture at a clinically relevant concentration seems to be stable at room temperature, at a wide range of pH values, for at least 4 days.

IMPLICATIONS: Small-dose ketamine is used with increasing frequency in the acute postoperative setting as an adjunct to traditional opioid analgesics. We show that a racemic ketamine and morphine solution at a clinically relevant concentration seems to be stable at room temperature at a wide range of pH values for at least 4 days.

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