Ketamine is an NMDA-receptor antagonist which can be used to decrease opioid tolerance.
Ketamine is a dissociative anesthetic (it does not cause patients to lose consciousness). It exerts its affects via acting as an NMDA-receptor antagonist. Its mechanism of action is similar to that of the illicit drug PCP. Ketamine has a number of side-effects, including acting as a cardiovascular stimulant, causing emergent delusion/hallucination, and increasing cerebral blood flow. Ketamine has been abused as a recreational drug.
Clary and Lawson discuss the toxic neurological affects of chronic high dose opioid use. Long term side-effects can include hyperalgesia, delirium, and myoclonus. Ketamine can be a useful adjunct in patients experiencing such side-effects as it can reduce chronic opioid need for some patients. Opioid rotation may also be beneficial in some patients.
Kapural et al. retrospectively analyzed ketamine's use as an opioid sparing agent. The authors found that IV ketamine infusion decreased long-term opioid use for some patients. There were no differences in pain scores for patients who received ketamine therapy versus those who did not. The ketamine arm of the study had a high drop out rate primarily due to experiencing no benefit.
Answer 1: Propofol is an anesthetic agent that acts via potentiation of GABA.
Answer 3: Fentanyl is an opioid anesthesic.
Answer 4: Ketorolac (toradol) is an NSAID.
Answer 5: Midazolam is a benzodiazapine that acts via potentiating GABA signaling.
Clary PL, Lawson P. Pharmacologic pearls for end-of-life care. Am Fam Physician. 2009 Jun 15;79(12):1059-65.
PMID:19530636 (Link to Abstract)
Kapural L1, Kapural M, Bensitel T, Sessler DI. Opioid-sparing effect of intravenous outpatient ketamine infusions appears short-lived in chronic-pain patients with high opioid requirements. Pain Physician. 2010 Jul-Aug;13(4):389-94.
PMID:20648208 (Link to Abstract)