Lost in conversion: navigating the challenges of converting intrathecal opioids to oral equivalents—a case report and literature review

BACKGROUND: Chronic intrathecal opioid use via intrathecal drug delivery system (IDDS), while effective in some patients, can lead to serious complications and side effects. Complications related to IDDS include mechanical/device malfunction, intrathecal catheter problems, infections, and provider errors. These issues often require urgent surgical intervention, IDDS removal, and abrupt discontinuation of the analgesic infusion. In these scenarios, the safe and effective transition to alternative opioid delivery routes such as intravenous or oral administration is critical. However, an accurate calculation of equianalgesic doses to ensure adequate pain control while minimizing the risk of withdrawal is not well documented. CASE REPORT: A patient in their 60s with a complex medical history, including chronic low back pain managed with IDDS for 30 years, presented with severe pain unresponsive to dose adjustments. Imaging revealed a catheter-related granuloma at thoracic 8 level, leading to intrathecal therapy discontinuation. A rapid weaning protocol reduced the intrathecal morphine dose by 10% daily, transitioning to systemic opioids based on pain severity and short-acting opioid needs. The final intrathecal-to-oral morphine conversion ratio by the time the pump was empty on day 10 was approximately 1:10. CONCLUSION: Current guidelines for intrathecal-to-systemic opioid conversion vary widely, with outdated literature suggesting a 1:300 ratio, whereas real-world cases report ratios between 1:2.5 and 1:70. Given this variability, a conservative, patient-specific approach is essential. Clinicians should consider pharmacokinetics, tolerance, and comorbidities, starting with lower conversion ratios and titrating carefully.