Technique was devised to beef up dextromethorphan (DM cough syrup) ) by combining it with quinidine sulfate which prevents the former from being metabolized IDrugs. 2010 Apr;13(4):254-65.
AVP-923, a combination of dextromethorphan hydrobromide and quinidine sulfate for the treatment of pseudobulbar affect and neuropathic pain.
Olney N, Rosen H. abstract here
- Dextromethorphan, a cough suppressant, is a NMDA receptor blocker – similar to ketamine but no where as good.
- Doses required for effect were huge and limited its use.
- 20-30 mg DM combined with quinidine sulphate 10 mg was found to be safe in pseudobulblar effect seen in amyotrophic lateral sclerosis (ALS) of Multiple Sclerosis.
- The combo is waiting for FDA approval
DM has been investigated before. In:
Anesthesiology: May 2002 – Volume 96 – Issue 5 – pp 1053-1061
Dextromethorphan and Memantine in Painful Diabetic Neuropathy and Postherpetic Neuralgia: Efficacy and Dose-Response Trials
Sang, Christine N. M.D., M.P.H.; Booher, Susan R.N.; Gilron, Ian M.D.; Parada, Suzan R.N.; Max, Mitchell B. M.D.H abstract here
- 400 gm DM or 55 mg memantine
Note – the Dextromethorphan cut the pain of Diabetic Neuropathy by 33% but didn’t touch post-Herpetic Neuralgia.
The amount of Dextromethorphan is huge alone, but with the quinidine sulphate, this problem has been fixed. You should not use quinidine sulphate on anyone with heart block or heart rhythm issues.
Besides quinidine, there are some other strong inhibitors of P450 2D6 (CYP2D6) enzyme as discussed in Wikipedia here
They include:
SSRIs:
citalopram
fluoxetine (prozac)
paroxetine
Some other antidepressants:
bupropion
duloxetine
A Combination of Amitriptyline and fluoxetine is commonly used in Fibromyalgia.
Duloxetine (Cymbalta) is commonly used in Fibromyalgia
DM has been tried in Fibromyalgia
The Intravenous Ketamine Test Predicts Subsequent Response to an Oral Dextromethorphan Treatment Regimen in Fibromyalgia Patients.
The Journal of Pain, Volume 7, Issue 6, Pages 391-398.
S. Cohen et al abstract
A subgroup of FM patient (those who respond to IV Ketamine) also respond to Dextromethorphan:
The dose required is all over the map. but on above meds should be considerably less.
I’ll let you know if I try it… Probably try 30 mg 2-4 times daily and see.