Low-Dose Ketamine Infusions for Neuropathic Pain: Evidence and Protocols

Low dose ketamine infusions may provide short-term pain relief for some people with refractory neuropathic pain, especially complex regional pain syndrome (CRPS), but the evidence does not establish one best dose, schedule, or long-term maintenance plan. Neuropathic pain is pain caused by a lesion or disease of the somatosensory nervous system. A qualified pain clinician should assess the diagnosis, treatment history, medical risks, and monitoring needs before an infusion is considered.

Ketamine blocks N-methyl-D-aspartate, or NMDA, receptors, which are involved in central sensitization, a state in which the nervous system becomes unusually responsive to pain signals. This article explains what the research supports, where the evidence remains limited, and what patients can discuss with a treating clinician.

Why ketamine is considered for neuropathic pain

Neuropathic pain can occur with diabetic peripheral neuropathy, postherpetic neuralgia, chemotherapy-induced peripheral neuropathy, spinal cord injury, phantom limb pain, and CRPS. Symptoms can include burning pain, electric-shock sensations, pain from light touch, and increased pain from normally painful stimuli.

Following nerve injury, increased signaling from peripheral nerves can promote changes in the spinal cord and brain. NMDA receptor activation is one part of this process. Research also examines glial cells, inflammatory signaling, and altered descending pain modulation. These mechanisms provide a rationale for ketamine, but a plausible mechanism alone does not predict an individual patient's response.

For a broader explanation of how ketamine may affect nervous-system adaptation, see neuroplasticity mechanisms and ketamine and neuroinflammation.

Clinical evidence: strongest for CRPS, less certain for other causes

Systematic reviews generally find that intravenous ketamine can produce short-term analgesia in neuropathic pain, while also stressing that studies use different populations, doses, infusion durations, and follow-up periods. The Cochrane review by Connolly and colleagues concluded that intravenous ketamine showed short-term benefit but that heterogeneity and limited follow-up restricted conclusions about long-term use.

CRPS has the most developed infusion literature. In a double-blind trial of 30 patients, Sigtermans and colleagues reported pain reduction after a multi-day S-ketamine infusion, with benefit observed through 12 weeks for the study group. A separate randomized trial by Schwartzman and colleagues evaluated a four-day infusion protocol and reported improvements in pain severity at follow-up. These are important findings, but they do not mean every person with CRPS will respond or that multi-day treatment is appropriate in every setting.

Small controlled studies have also reported reduced evoked pain or allodynia in diabetic neuropathy and postherpetic neuralgia. Evidence for chemotherapy-induced neuropathy and several other etiologies is thinner. The 2018 consensus guidelines from the American Society of Regional Anesthesia and Pain Medicine, American Academy of Pain Medicine, and American Society of Anesthesiologists discuss the evidence and safety considerations for intravenous ketamine in chronic pain.

What an infusion protocol may involve

There is no universal protocol for low dose ketamine in neuropathic pain. Outpatient studies and clinical protocols often use subanesthetic intravenous doses over roughly 30-60 minutes, while severe refractory CRPS has been studied with longer, closely monitored infusions. Dose, route, interval, and the decision to repeat treatment should be set by the treating team rather than copied from a study or another patient's plan.

Clinicians may track pain intensity, allodynia, daily function, sleep, medication use, adverse effects, and how long any benefit lasts. That record helps distinguish a meaningful response from a brief change that does not improve function. Readers comparing treatment timing can review how low-dose ketamine treatments may be spaced, while keeping in mind that an educational article cannot replace a personal protocol.

Who may be a candidate, and who may need another approach first

Ketamine is generally discussed as an option for refractory pain, meaning pain that has persisted despite appropriate evaluation and standard treatments. A clinician may look for a clear neuropathic diagnosis, documented functional impact, prior treatment trials, coexisting mood or substance-use concerns, cardiovascular history, and the patient's ability to participate in monitored care.

It may be less suitable when the risks of transient blood pressure elevation, altered perception, sedation, or psychiatric symptoms cannot be managed safely. The available research does not provide a reliable test that can tell in advance who will respond. Quantitative sensory testing is being studied as a possible tool, but it is not a validated universal selection rule for ketamine infusions.

Safety and monitoring questions to raise before treatment

Ketamine can cause dissociation, nausea, dizziness, sedation, and temporary increases in blood pressure or heart rate. The chronic-pain consensus guidelines describe monitoring practices that may include blood pressure measurement, pulse oximetry, and assessment of consciousness and adverse effects. The appropriate level of monitoring depends on the dose, route, patient history, and setting.

Repeated courses also merit discussion of cumulative exposure. Reports of liver injury and lower urinary tract symptoms have raised concerns in some chronic-use settings. These concerns do not establish the same risk for every supervised infusion regimen, but they support individualized follow-up when treatment is repeated. See the site's overview of cardiovascular monitoring during ketamine care and common ketamine side effects for related questions to bring to an appointment.

Bottom line

Low dose ketamine infusions have a credible NMDA-based rationale and can provide short-term analgesia for selected people with neuropathic pain. CRPS has the strongest supporting infusion studies. For diabetic neuropathy, postherpetic neuralgia, spinal cord injury pain, and other conditions, the evidence is more limited and should be interpreted with care.

A good decision starts with a confirmed diagnosis, realistic goals, a review of alternatives, and a clinic that can explain its monitoring and follow-up plan. The NCBI Bookshelf review of ketamine in acute and chronic pain management provides additional clinical background, and the CDC Clinical Practice Guideline for Prescribing Opioids for Pain outlines broader principles for individualized chronic pain care.