(Lorne's autocorrect is mixing up posters and drugs now)
You know, since we're all about the codeine problems lately, now there's two drugs that both need CYP2D6 to get to the opioid metabolites.
Tramadol has no opioid receptor affinity by itself, and needs to be metabolised to desme-tram for that.
Pizzalover:
I wouldn't be surprised if the slowly formed (in slow release) and longer-lived desmetramadol, plus some tolerance, lingering around is blunting your codeine enjoyment. Although 100mg isn't a tremendous amount and nine hours isn't that long. It probably is only tolerance. Only solution is to space the two drug uses out.
Aussie_Kiss:
You said you get relief with the oxycodone, but I guess it's a bit more precious, is why you save it for breakthrough pain? Cause if that works, you should use it instead of redlining tramadol dosage.
You too might be one of those CYP2D6 people or more likely drug-interacting people, since you need that enzyme function to get all the pain relief from tramadol (but not oxycodone). You asked about potentiating, and I hope you didn't already try anything like grapefruit juice, because that inhibits the enzyme you actually need.
You can get a list of the hundreds of foods and drugs that inhibit that enzyme online. You might be taking an anti-histamine to try to potentiate too, and be counter-productive.
Or, tramadol might not be the drug for you. Please don't take the max dose all at once, do like you were doing, but more spread out in time. You can take an antihistamine to sleep later, don't worry about that. Just don't start seizing.