Canterbury DHB

Context

Ketamine Information Sheet

Ketamine injection 200 mg/2 mL

Ketamine has been used for over 30 years as a dissociative general anaesthetic. At anaesthetic doses (up to 2 mg/kg IV or 10 mg/kg IM for induction) it activates the limbic system and depresses the cerebral cortex, producing profound analgesia, slight respiratory depression, cardiovascular stimulation, and amnesia.

This guide is for ketamine when it is being used for pain management in the palliative setting.

Ketamine is an N-methyl-D-aspartate (NMDA) receptor antagonist. NMDA receptors are glutamate receptors and glutamate is the main excitatory transmitter in the CNS. NMDA receptor stimulation is also involved in the development of opioid tolerance and in neuropathic pain. The analgesic role of ketamine (when given in sub-anaesthetic doses) appears to be linked to an alteration in opioid sensitivity as part of its clinical effect. It also has kappa and mu opioid-like actions.

Long term opioid therapy is commonly administered for the management of severe cancer pain. Increasing doses of opioids can lead to opioid tolerance (a phenomenon by which repeated doses of opioid produce decreasing effects or increasingly large doses are required to maintain the previous effect). Rapid opioid escalation due to either worsening of pain or the development of tolerance is a negative prognostic factor for the development of adverse effects and suggests limited opioid responsiveness. The phenomena of “wind-up” can occur in this setting. This is where pain intensifies as the opioid dose is increased, a process also believed to be mediated by the NMDA receptor. NMDA receptor antagonists have been reported to improve analgesia in those whose response to opioids is failing. Also, ketamine can be used as boluses intravenously or subcutaneously for pain prophylaxis prior to procedures such as burns dressings. In palliative care, bolus doses of 10-25 mg subcutaneously stat are commonly used. There is a nominal maximum dose of 500 mg in 24 hours, generally given as a continuous subcutaneous infusion.

As with the management of any symptom, an accurate clinical assessment is critical to successful treatment with ketamine. NMDA antagonists such as ketamine may not be the answer to all pains that are difficult to control with standard opioid and adjuvant analgesics. A referral to Palliative Care is strongly recommended. Patients with neuropathic, inflammatory, ischaemic, and phantom limb pain groups and those with the triad of allodynia, hyperalgesia, and prolongation of the pain response (the classical features of neuropathic pain and “wind-up”) are most likely to have a favourable response to ketamine. The option of rotating onto methadone instead of using ketamine may also need to be considered, as this opioid analgesic also has some NMDA receptor antagonist properties.

Pharmacology

Precautions

Side effects

Dosing Recommendations

When used as follows, ketamine is best administered in a hospital or hospice setting, under the supervision of a palliative care specialist. The use of ketamine is opioid sparing - be prepared to reduce the opioid dose significantly as the ketamine takes effect.

More information and advice is available

For more information and advice within working hours, contact either the Christchurch Hospital Palliative Care Service on (03) 364 1473 or the Nurse Maude Hospice on (03) 375 4274. After hours, contact the Christchurch Hospital operator on (03) 364 0640 and ask for the palliative care clinician on call.

About this Canterbury DHB document (58013):

Document Owner:

Kate Grundy (see Who's Who)

Issue Date:

March 2016

Next Review:

March 2018

Keywords:

Note: Only the electronic version is controlled. Once printed, this is no longer a controlled document. Disclaimer

Topic Code: 58013