Paraphernalia - Tramadol vs. O-desmethyltramadol (repeated dosing)

[Paracelsus]

I have often read online (on this forum and in other places) that repeated dosing makes tramadol better because it allows tramadol to clear while the desired metabolite O-desmethyltramadol builds up in the bloodstream.

I started this thread to find out if there is any evidence that this is true and proven. I have only seen concentration/time diagrams for tramadol alone and not O-desmethyltramadol. If anyone has access to details on tramadol and O-dmt pharmacokinetics which indicate that this is plausible, please share. Concentration-time diagrams for both tramadol and O-dmt which show concentrations following repeated dosing would also be useful.

If this would be true, timed-release tramadol (Ultram ER and the like) would have a higher abuse potential than instant-release tramadol.