A case with a trend of QT interval prolongation due to the introduction of methadone to a pancreatic cancer patient on levofloxacin

Background As methadone can prevent the development of opioid resistance, it has application in alleviating cancer-related pain that proves challenging to manage with other opioids. QT interval prolongation is a serious side effect of methadone treatment, with some reported deaths. In particular, owing to the increased risk of QT interval prolongation, caution should be exercised when using it in combination with drugs that also prolong the QT interval. Case presentation This study presents a case in which methadone was introduced to a patient (a man in his 60s) already using levofloxacin, which could prolong the QT interval—a serious side effect of methadone treatment—and whose QTc value tended to increase. Given that levofloxacin can increase the risk of QT interval prolongation, we considered switching to other antibacterial agents before introducing methadone. However, because the neurosurgeon judged that controlling a brain abscess was a priority, low-dose methadone was introduced with continuing levofloxacin. Owing to the risks, we performed frequent electrocardiograms. Consequently, we responded before the QTc increased enough to meet the diagnostic criteria for QT interval prolongation. Consequently, we prevented the occurrence of drug-induced long QT syndrome. Conclusions When considering the use of methadone for intractable cancer pain, it is important to eliminate possible risk factors for QT interval prolongation. However, as it may be difficult to discontinue concomitant drugs owing to comorbidities, there could be cases in which the risk of QT interval prolongation could increase, even with the introduction of low-dose methadone. In such cases, frequent monitoring, even with simple measurements such as those used in this case, is likely to prevent progression to more serious conditions.