A 36-year-old female with metastatic breast cancer involving bones, liver, lung, and pleura/chest wall with worsening back pain received weight-based intravenous (IV) ketamine and was transitioned to oral ketamine for cancer-related neuropathic pain. She had responded poorly to outpatient pain regimen of oxycodone sustained and immediate release, hydromorphone, gabapentin, and duloxetine (approximate 480 mg total oral morphine equivalents [OME]), reporting an initial pain score of 10/10. She was started on hydromorphone parenteral patient-controlled analgesia (PCA) bolus dose in addition to her outpatient regimen. Despite escalating doses of opioids and the addition of a lidocaine 5% patch, the patient's pain remained uncontrolled 6 days after admission. On hospital day 7, utilizing a hospital weight-based ketamine protocol, the patient was started on subanesthetic doses of ketamine at 0.2 mg/kg/h (288 mg/24 h) and titrated over 2 days to 0.4 mg/kg/h (576 mg/24 h). Then, a 3-day rotation from intravenous to oral ketamine was initiated, and the patient was discharged on ketamine oral solution, 75 mg every 8 hours. When the patient's dose was increased to 0.4 mg/kg/h, adequate pain relief was charted by the nurse within 120 minutes, "patient pain free and resting comfortably." Her pain continued to be well managed, with an average pain score of 5/10 with the ketamine continuous infusion and sustained with conversion to oral ketamine without any report of side effects. This was a 37% reduction in pain scores. With the patient's stabilized dose of ketamine, opioid requirements decreased by 61.4% (1017.5 mg reduction in total OME). The use of weight-based dosing of IV continuous infusion and transition to oral ketamine was effective and tolerable in the management of opioid-refractory, neuropathic cancer pain. It is hoped that this case report promotes a discussion regarding ketamine dosing in refractory neuropathic cancer pain.
Keywords: NMDA antagonist; cancer; ketamine; pain; refractory.