Abstract

Background: Methadone is a synthetic opioid that is useful in treating complex pain syndromes. However, its potential to prolong the QTc interval may lead to a serious cardiac risk, requiring careful monitoring and individualized care. Switching from methadone to another opioid has not been well studied and could prove difficult because it does not have a recognized dose conversion ratio.

Case: A 17-year-old male with metastatic nasopharyngeal carcinoma had worsening QTc prolongation while on methadone. So, a decision was made to stop methadone and rotate him to morphine. A conservative rotation ratio of 1:3 (methadone: morphine) was used, with a 20% further dose reduction to account for incomplete cross-tolerance. Upon follow-up, the dose of morphine was tapered up to 150 mg MEDD. He was then switched to fentanyl due to tolerance. His pain was eventually controlled on a fentanyl dose of 150 mcg /hr.

Conclusion: Opioid rotation from methadone can be performed safely with close monitoring. Further tapering up of the new opioid dose is expected to reach optimum pain control. Although we used a 1:3 (methadone: morphine) conversion ratio as a start, the dose that controlled the pain was almost 12 times more than the initially calculated dose.

Keywords

synthetic opioid,complex pain syndromes,nasopharyngeal carcinoma, fentanyl dose chemoimmunotherapy, radiotherapy, uncontrolled pain, numerical pain scale