My girlfriend has painful menses, and no non opiate/opioid analgesic is helping her. We noticed a fact, that tramadol 50 mg fully stops the pain, but codeine at 60 mg even with 1000 mg of paracetamol has no influence. As I found codeine is almost equivalent to tramadol by weight basis.
As she uses duloxetine (SNRI antidepressant, a moderate CYP2D6 ihnibitor), I thought the inhibition of a ferment converting codeine to morphine may play a role here, but tramadol also is metabolized to desmetyltramadol via the same ferment.
What can be the mechanism of tolerance to antinociceptive effects of codeine and normal reaction to tramadol?
PS. We know about the possibility of serotonin syndrome form mixing SNRI and tramadol, but at the doses she use it seems there are no symptoms of SS.
As she uses duloxetine (SNRI antidepressant, a moderate CYP2D6 ihnibitor), I thought the inhibition of a ferment converting codeine to morphine may play a role here, but tramadol also is metabolized to desmetyltramadol via the same ferment.
What can be the mechanism of tolerance to antinociceptive effects of codeine and normal reaction to tramadol?
PS. We know about the possibility of serotonin syndrome form mixing SNRI and tramadol, but at the doses she use it seems there are no symptoms of SS.