NMDA receptor antagonists for pain

NMDAs receive their name from the N-methyl-D-aspartate (NMDA) receptor located in the spinal cord. These receptors commonly become hypersensitive in people who have experienced cancer, arthritis or nerve injury associated with diabetes, shingles or post mastectomy. Activity at this receptor site is also believed to be responsible for the tolerance seen with opioid medications. A medication that reduces or blocks activity at this receptor should reduce pain and increase the effectiveness of opioids so increasingly larger doses are not needed. NMDA antagonists include:

• Amantadine (used for parkinson's disease and influenza)
• Dextromethorphan (an over the counter cough suppressant, recreational drug)
• Ethanol (alcohol intoxication)
• Ketamine (anesthetic and recreational drug)
• Memantine (Alzheimer's disease)
• Methadone (pain killer and narcotic addiction)
• Nitrous oxide ('laughing gas'-used in dentistry for pain relief and as an anesthetic)
• Phencyclidine (PCP-anesthetic and recreational drug)
• Tramadol (an opioid painkiller)
• Ketobemidone (an opioid painkiller)

Side effects -The side effects of NMDA Receptor Antagonists continue to limit their usefulness. Possible side effects include:

• hallucinations, paranoid delusions
• confusion, difficulty concentrating, learning and memory difficulties
• agitation
• altered mood
• nightmares
• movement difficulties
• Large doses can lead to brain damage

Recreational use: Unfortunately the hallucinogenic and mood altering effects of NMDA antagonists have made them popular as recreational drugs. When used in this way high dosages, poor quality drugs, and mixing with other drugs has been associated with permanent brain damage and death.