Theoretically NMDA receptor antagonists can be useful for chronic pain that involves nerves, because this drug has effects on nerves. There several drugs of this class that are approved for different indications: ketamine, methadone, memantine, amantadine, and dextromethorphan. Amantadine is approved for treatment of Alzheimer’s disease and it has had mixed results for treating pain in clinical trials. A double-blind, randomized, placebo-controlled trial there was an 85% pain reduction with amantadine versus 45% with placebo (P = .009) at the end of the infusion. When comparing mean pain intensity 48 hours prior to and following treatment, amantadine had a 31% reduction in pain (P = .006), whereas the placebo showed an insignificant pain reduction of 6% (P = .40).
In contrast to these positive results, Fukui et al conducted a study of amantadine in 19 patients who failed to respond to the conventional treatments for neuropathic pain, including anti-convulsants, antidepressants, and nerve blocks. Adverse effects were experienced in 52.6% of the patients, including dry mouth, drowsiness, hallucinations, excitation, irritation, dizziness, dyskinesia, and loss of hair and teh drug was not proven effective.
There are no guidelines that currently support the use of amantadine for treating chronic pain.
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