Low-dose ketamine as an adjuvant for pain control in a cancer patient: a case report

Pain is highly prevalent among people with cancer and often remains poorly controlled despite specialist care. The extracted text notes that 55–66% of cancer patients experience at least moderate pain despite treatment in a pain management setting, and that opioid therapy—the usual mainstay—carries well‑known harms including nausea, constipation, sedation, neuroexcitation and a narrow therapeutic window. Rapid escalation of opioid doses driven by tolerance is described as problematic, and the authors frame a clear need for non‑opioid or opioid‑sparing alternatives for persistent cancer pain. This case report examines low‑dose ketamine (LDK), an N‑methyl‑D‑aspartate (NMDA) receptor antagonist, as an adjuvant to opioid therapy in a single patient with metastatic prostate cancer whose pain remained refractory on high‑dose opioids. The study aims to document the clinical course, pain scores and opioid consumption before, during and after a short course of LDK infusion, and to illustrate potential benefits and tolerability of this approach in a palliative care context.

This is a single‑patient case report of a 55‑year‑old man with metastatic Gleason 9 prostate adenocarcinoma and bony metastases causing mixed neuropathic and somatic pain. The study received institutional review board approval; the extracted text states that informed consent from the patient could not be obtained posthumously because next of kin were untraceable. Pain was assessed primarily using the Numerical Rating Scale (NRS), with routine monitoring while on infusion. Patel and colleagues describe a local LDK protocol established under federal and institutional guidelines that allowed intravenous ketamine titration below 0.5 mg/kg as an adjunct to opioid therapy. The continuous infusion concentration was 100 mg ketamine in 100 mL 5% dextrose (1 mg/mL). A 3‑day escalating infusion schedule was used: 0.1 mg/kg/hr on Day 1, 0.2 mg/kg/hr on Day 2, and 0.3 mg/kg/hr on Day 3. A maximum push dose is reported in the extracted text, though units are presented ambiguously. The NRS was recorded every 4 hours during infusion and observational data were collected within the first 24 hours regarding pain characteristics, vital signs, respiratory depression, tolerance and overall satisfaction. Opioid utilisation was quantified as oral morphine milligram equivalents (MME). The team compared average total daily MME for three periods: 30 days before the LDK infusion, during the LDK infusion, and 30 days after the infusion. The extracted text lists the patient’s baseline opioid exposure as 458.8 MME per day. Safety monitoring focused on known ketamine adverse effects such as hallucinations and agitation.

Prior to ketamine, the patient reported persistent high pain with an NRS score of 9/10 while receiving a calculated 458.8 MME per day. After the three‑day LDK infusion (0.1 → 0.2 → 0.3 mg/kg/hr), reported pain decreased during treatment to an average NRS of 5/10. The authors report a 32.43% reduction in opioid usage associated with the initial pain improvement. Over the 30 days following the infusion the patient’s mean pain score averaged 4.75 on the NRS, which the authors describe as roughly a 50% reduction from the pre‑infusion score. Objective opioid consumption also fell: total daily MME declined from the baseline 458.8 to 310 MME in the 30 days after infusion. The extracted text records a 16.67% reduction in methadone use and complete cessation of fentanyl. No ketamine‑related hallucinations or agitation were reported in this case, and no other adverse events are noted. A nursing progress note is cited indicating the patient appeared to be in "great spirits" after the infusion, and the authors report an associated improvement in mood alongside analgesic effects.

The authors place the case within the broader problem of under‑recognised and undertreated cancer pain and the limitations of sole reliance on opioids. They argue that LDK may serve as an effective opioid‑sparing adjunct in refractory cancer pain and highlight mechanistic plausibility: ketamine’s NMDA antagonism can reduce pain sensitisation and may enhance opioid receptor responsiveness, thereby prolonging opioid analgesia. Patel and colleagues also discuss ketamine’s reported antidepressant actions and raise the possibility that some of the analgesic benefit could relate to amelioration of an emotional component of pain. The discussion acknowledges important uncertainties. The authors note that previous cancer pain studies of LDK have been small, heterogenous in interventions and outcome measures, and that titrated dose trials across varied pain scenarios are still needed to establish safety and optimal regimens. They also cite the subjective nature of the NRS as a diagnostic limitation. Ethical limitations are explicit in the extracted text: although institutional review board approval was obtained, the patient died and the authors were unable to secure informed consent from next of kin. The authors call for further research to determine efficacy, dosing schedules and routes of administration before LDK can be more widely recommended in palliative oncology.

This selective case illustrates that a short course of low‑dose intravenous ketamine (<0.5 mg/kg titrated over three days) was associated with marked and sustained reductions in pain scores and a substantial decrease in opioid consumption for one patient with advanced metastatic prostate cancer. The authors conclude that LDK shows potential as an adjunct in palliative pain management but emphasise that additional research is required to confirm efficacy, define optimal dosing and administration routes, and establish safety in broader cancer populations.