Both duloxetine and pregabalin work by restoring brain down pain inhibition. Hence the work in people who have deficits in this system. There is a simple test to confirm functioning.
Eur J Pain. 2017 Jul;21(6):997-1006. doi: 10.1002/ejp.1007.
Endogenous analgesic effect of pregabalin: A double-blind and randomized controlled trial.
Sugimine S et al
“The analgesic effect of pregabalin depends on the original endogenous analgesia status. Its effect on conditioned pain modulation (CPM) was stronger for subjects with lower original endogenous analgesia, suggesting that the mechanism of pregabalin involves the improvement of endogenous analgesia.”
DULOXETINE HAS NO EFFECT ON EXCITATORY SPINAL ACTIVITY BUT RESTORES CONDITIONED PAIN MODULATION IN FIBROMYALGIA PATIENTS
Poster Canadian Pain Society 37 th Annual Scientific Program May 24-27, 2016 Vancouver, BC
“duloxetine seems to restore CPM [Conditioned Pain Modulation] efficiency, but only in patients with inefficient CPM before treatment.”
How does one gauge the effectiveness of the descending inhibitory pathways?
stimulate a spot and find painful level with laser etc.
stimulate after doing a cold pressor test ( easy enough – have patient put hand in ice water until s/he finds it painful)
After cold pressor, threshold for pain should be higher because endorphin-like descending inhibition has kicked in.
Fact of the matter is even much more simple – a technique work out by Dr. Serge Marchand in Sherbrooke Que, – Poke at a spot on shoulder that is sore – wait ?5 minutes – I thought you’d have to repoke to see, but often the patient will say it is still sore – confirming descending inhibition has not kicked in.
Hence a simple shoulder test might confirm that descending inhibition works or not – if it doesn’t both duloxetine and pregabalin are more likely to work.