Drug-Related Side Effects of Long-term Intrathecal Morphine Therapy

Abstract

Background: The introduction of intrathecal opioid administration for intractable chronic non-malignant pain and cancer pain is considered as one of the most important breakthroughs in pain management. Morphine, the only opioid approved by FDA for intrathecal administration, has been increasingly utilized for this purpose. For over 3 decades, there have been numerous reports on the non-nociceptive side effects associated with ever increasing long-term intrathecal morphine usage. Objectives: To review the literature on side effects due to long-term intrathecal morphine therapy with discussions of alternate treatment options. Design: English-language publications were identified through MEDLINE search and the bibliographies of identified articles were reviewed. Results: Most side effects of intrathecal morphine therapy are dose dependent and mediated by opioid receptors. Common ones include nausea, vomiting, pruritus, urinary retention, constipation, sexual dysfunction, and edema. Less common ones include respiratory depression, and hyperalgesia. Catheter tip inflammatory mass formation is a less common complication that may not be mediated by opioid receptors. Conclusion: The utilization of intrathecal morphine administration for cancer and intractable non-malignant chronic pain represents an important leap forward in pain management. Yet, a wide variety of non-nociceptive side effects may also occur in susceptible patients. The side effects due to intrathecal morphine administration are mostly mediated by opioid receptors. Treatment usually involves the utilization of opioid receptor antagonist, such as naloxone. Patients considering intrathecal opioid pump therapy should be informed and advised about the possible side effects associated with longterm intrathecal morphine administration prior to placement of a permanent morphine infusion pump. Key words: side effects, intrathecal morphine, opioid receptors