Ketamine for chronic pain: risks and benefits

Summary & key facts

Ketamine, a drug originally used as an anaesthetic, can strongly reduce nerve-related chronic pain while it is being given. A few studies that gave ketamine for several days reported pain relief lasting up to three months. However, the drug can cause strong side effects and long-term risks, so doctors say it should be used only for people with severe nerve pain that has not improved with other treatments, and patients need careful monitoring.

Key facts:

• Ketamine is used to treat several long-term pain conditions, especially pain caused by nerve damage (neuropathic pain).
• Low doses of ketamine given as short infusions produce strong pain relief, but this relief usually lasts only while the drug is being given.
• Three studies that used longer ketamine infusions lasting 4 to 14 days reported pain relief that lasted for up to about three months after the infusion.
• Common side effects seen in clinical studies include psychedelic symptoms such as hallucinations, memory problems, panic attacks, nausea and vomiting, drowsiness, and increased heart rate and blood pressure. A small number of patients showed liver damage.
• Recreational use of ketamine is rising and brings extra risks not always seen in medical use, including bladder and kidney damage, long-lasting memory problems, and persistent odd or psychotic-like behaviour. These risks are hard to compare directly with medical use because recreational users often take much larger or repeated doses and use other drugs.
• In medical settings ketamine is generally tolerated, and doctors sometimes give benzodiazepines (a type of sedative) to reduce the psychedelic side effects.
• Doctors should closely monitor people receiving ketamine for effects on the brain and nervous system, blood pressure and heart function, kidney and liver health, and signs of misuse or addiction.
• Because evidence about long-term benefits and harms is still limited, the authors say ketamine should be reserved for people with severe nerve pain that has not responded to other treatments until better proof is available.

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

Addiction Chronic Pain Chronic pain Lack of energy or motivation Panic