Ketamine for chronic pain: risks and benefits

Summary & key facts

Researchers reviewed studies of the anaesthetic drug ketamine for long-lasting pain, especially nerve-related pain. Low doses often cut pain while the drug is being given. In a few studies where ketamine was given for several days, people had less pain for up to a few months afterward. The drug can cause strong side effects, including hallucinations, memory problems, panic-like reactions, nausea, sleepiness, heart stimulation, and sometimes liver problems. Recreational use brings extra harms. Because the risks and long-term benefits are not settled, the authors say ketamine should be kept for people with severe nerve pain that has not responded to other treatments, and patients need close medical monitoring.

Key facts:

• Ketamine can produce strong short-term pain relief for nerve-related pain, but this relief usually lasts only while the drug is being given.
• Three studies where ketamine was given continuously for several days (about 4 to 14 days) reported pain relief that lasted for up to about three months afterward.
• Scientists think ketamine works mainly by blocking a brain receptor involved in pain signals (called NMDA), and it may also reduce brain inflammation and boost the body's own pain-blocking systems.
• Common side effects seen in clinical studies include hallucinations or psychedelic symptoms, memory problems, panic attacks, nausea or vomiting, sleepiness, and increased heart activity; a minority of patients showed liver damage.
• Recreational ketamine use is rising and is linked to extra risks not always seen in medical settings, such as bladder and kidney damage and persistent memory or behavior problems.
• In hospitals, ketamine is generally better tolerated when doctors also give sedating drugs called benzodiazepines to reduce the psychedelic side effects.
• Because of remaining uncertainty about long-term benefits, safety, and cost, the authors recommend reserving medical ketamine for people with severe nerve pain that has not responded to other treatments, and closely watching the brain, heart, kidneys, liver, and any signs of misuse while it is given.

Abstract

The anaesthetic ketamine is used to treat various chronic pain syndromes, especially those that have a neuropathic component. Low dose ketamine produces strong analgesia in neuropathic pain states, presumably by inhibition of the N-methyl-D-aspartate receptor although other mechanisms are possibly involved, including enhancement of descending inhibition and anti-inflammatory effects at central sites. Current data on short term infusions indicate that ketamine produces potent analgesia during administration only, while three studies on the effect of prolonged infusion (4-14 days) show long-term analgesic effects up to 3 months following infusion. The side effects of ketamine noted in clinical studies include psychedelic symptoms (hallucinations, memory defects, panic attacks), nausea/vomiting, somnolence, cardiovascular stimulation and, in a minority of patients, hepatoxicity. The recreational use of ketamine is increasing and comes with a variety of additional risks ranging from bladder and renal complications to persistent psychotypical behaviour and memory defects. Blind extrapolation of these risks to clinical patients is difficult because of the variable, high and recurrent exposure to the drug in ketamine abusers and the high frequency of abuse of other illicit substances in this population. In clinical settings, ketamine is well tolerated, especially when benzodiazepines are used to tame the psychotropic side effects. Irrespective, close monitoring of patients receiving ketamine is mandatory, particularly aimed at CNS, haemodynamic, renal and hepatic symptoms as well as abuse. Further research is required to assess whether the benefits outweigh the risks and costs. Until definite proof is obtained ketamine administration should be restricted to patients with therapy-resistant severe neuropathic pain.

Topics

Anesthesia and Sedative Agents Pain Mechanisms and Treatments Treatment of Major Depression

Categories

Health Sciences Medicine Pharmacology

Tags

Adverse effect Analgesic Anesthesia Chronic pain Environmental health Intensive care medicine Ketamine Medicine Nausea Neuropathic pain Pharmacology Population Psychiatry Vomiting

Substances

Ketamine

Conditions & symptoms

Chronic Pain Chronic pain