Efficacy and safety of oral ketamine for the relief of intractable chronic pain: A retrospective 5-year study of 51 patients

Eur J Pain. 2015 Aug;19(7):984-93. doi: 10.1002/ejp.624. Epub 2014 Nov 10.


Background: This work summarizes the efficiency, failures and adverse effects of oral administration of ketamine at home for intractable pain.

Methods: This 5-year retrospective study involved testing ketamine by intravenous in-hospital administration, then a conversion to an oral route, or oral treatment directly administered at home. The daily intravenous dose was increased by steps of 0.5 mg/kg to attain an effective daily dose of 1.5-3.0 mg/kg. Pain was evaluated on a numeric scale from 0 to 10, and evidence of adverse effects was collected every day. The effective daily dose was delivered orally (three to four intakes). If effective, ketamine was continued for 3 months. Short infusions or direct oral treatment began with a 0.5-mg/kg dose, then the daily ketamine dose was increased in 15- to 20-mg increments.

Results: Among 55 cases (51 patients, neuropathic pain 60%), the mean effective oral dose was 2 mg/kg. Ketamine was effective in 24 patients (44%, mean pain reduction 67 ± 17%), partially effective in 20% (mean pain reduction 30 ± 11%), with a mean opioid sparing of 63 ± 32%, and failure in 22%. Half of the patients experienced adverse effects, but only eight had to stop treatment. For patients with opioid therapy, failure of ketamine was less frequent (7% vs. 36%; p < 0.02), with fewer adverse effects (33% vs. 68%; p < 0.01).

Conclusions: Pain was reduced or abolished in two-thirds of patients under ketamine therapy; ketamine was effective for patients taking opioids and resulted in few adverse effects.

MeSH terms

  • Administration, Intravenous
  • Administration, Oral
  • Adult
  • Aged
  • Analgesics, Opioid / administration & dosage
  • Analgesics, Opioid / therapeutic use
  • Anesthetics, Dissociative / administration & dosage
  • Anesthetics, Dissociative / adverse effects
  • Anesthetics, Dissociative / therapeutic use*
  • Chronic Pain / drug therapy*
  • Female
  • Humans
  • Ketamine / administration & dosage
  • Ketamine / adverse effects
  • Ketamine / therapeutic use*
  • Male
  • Middle Aged
  • Neuralgia / drug therapy
  • Pain Measurement / drug effects
  • Pain, Intractable / drug therapy*
  • Patient Safety
  • Retrospective Studies


  • Analgesics, Opioid
  • Anesthetics, Dissociative
  • Ketamine