Efficacy of outpatient ketamine infusions in refractory chronic pain syndromes: a 5-year retrospective analysis

Pain Med. 2012 Feb;13(2):263-9. doi: 10.1111/j.1526-4637.2011.01241.x. Epub 2011 Sep 21.


Objective: We evaluated whether outpatient intravenous ketamine infusions were satisfactory for pain relief in patients suffering from various chronic intractable pain syndromes.

Design: Retrospective chart review.

Setting and patients: Following Institutional Review Board approval, we retrospectively analyzed our database for all ketamine infusions administered over 5 years from 2004 to 2009.

Outcome measures: Data reviewed included doses of intravenous ketamine, infusion duration, pain scores on visual analog scale (VAS) pre- and post-procedure, long-term pain relief, previous interventions, and side effects. All patients were pretreated with midazolam and ondansetron.

Results: We identified 49 patients undergoing 369 outpatient ketamine infusions through retrospective analysis. We excluded 36 infusions because of missing data. Among our patients, 18 (37%) had a diagnosis of complex regional pain syndrome (CRPS). Of the remaining 31 (63%) patients, eight had refractory headaches and seven had severe back pain. All patients reported significant reduction in VAS score of 5.9 (standard error [SE] 0.35). For patients with CRPS, reduction in VAS score was 7.2 (SE 0.51, P < 0.001); for the others, the reduction was 5.1 (SE 0.40, P < 0.001). The difference of 2.1 between groups was statistically significant (SE 0.64, P = 0.002). In 29 patients, we recorded the duration of pain relief. Using the Bernoulli model, we found (90% confidence interval) that the probability of lasting pain relief in patients with refractory pain states was 59-85% (23-51% relief over 3 weeks).

Conclusions: We conclude that in patients with severe refractory pain of multiple etiologies, subanesthetic ketamine infusions may improve VAS scores. In half of our patients, relief lasted for up to 3 weeks with minimal side effects.

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Ambulatory Care* / methods
  • Analgesics / administration & dosage*
  • Analgesics / adverse effects
  • Chronic Pain / drug therapy*
  • Chronic Pain / physiopathology
  • Female
  • Humans
  • Infusions, Intravenous / adverse effects
  • Ketamine / administration & dosage*
  • Ketamine / adverse effects
  • Male
  • Middle Aged
  • Pain, Intractable / drug therapy*
  • Pain, Intractable / physiopathology
  • Retrospective Studies
  • Time Factors
  • Treatment Outcome
  • Young Adult


  • Analgesics
  • Ketamine