Brief Answer:
Zapain is stronger.

Detailed Answer:
but at this level of complexity, it's not predictable.

First, tramadol is not mainly a narcotic. It has some narcotic effects and some effects on nerves. the active ingredient in zapain is codeine which is a narcotic plain and simple.

BUT other factors come into play. First, obviously, is how much of each one is taking. A high dose of one is more than a teeny-weeny dose of another. Both of these particular drugs are much more constrained on what dose you can give than nearly any other narcotic. Tramadol gets really dangerous outside of its intended dose range due to causing seizures. While codeine has a lot of doses that could be given, it is mixed in with tylenol, which can cause an overdose so, it's dosing is also limited.
The top amount is 300 mg a day of tramadol and about four zapain pills a day (120 mg codeine). Tramadol might cover the day slightly better because zapain is stretching it to be a 6 hr drug...but 6 times a day is getting to be a bit high amount of tylenol AND you should NEVER give ANY TYLENOL on top of zapain.

http://clincalc.com/opioids/
is a conversion tool that shows that 120 mg of codeine equals 175 of tramadol and the usual dose of tramadol is 150 so... slightly more from the zapain.

BUT
1) tramadol also has effects on nerves so if it were a nerve injury or pain from sick nerves it would do more and last longer
2) codeine doesn't technically do anything. It is metabolized in the brain to morphine and that is the active chemical. AND how much is made into morphine varies between individuals with many people not making any and codeine not working at all. And a few where it works but lasts very briefly.
http://www.fda.gov/downloads/AdvisoryCommittees/CommitteesMeetingMaterials/PediatricAdvisoryCommittee/UCM343582.pdf

so, bottom line, they are about the same except the individual reaction to them is going to totally change how well they work and this is mostly unpredictable but you'd know about an hour after the dose. In individuals it is likely that one is going to be way better than the other but you can't tell ahead of time. If one worked acceptably, stick with it. Both are safe and neither is at a high dose. Neither is likely to cause addiction if used for the time needed for surgery (generally about a week maybe less; they are incredibly UNLIKELY to cause addiction).

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Brief Answer:
yes you can

Detailed Answer:
just make sure the tramadol does not have tylenol inside of it... ULTRACET is tramadol with tylenol and that would be an overdose (potentially) of tylenol when mixed with codeine with tylenol.

The two drugs are metabolized by the same system of the liver so there is some potential for drug interaction and there is a lot of genetic quirks on these same liver metabolizing enzymes with some people not metabolizing the drug at all and other metabolizing them really fast.

Fundamentally, you shouldn't use drugs that have a low safety margin. Codeine has a large safety margin, tramadol has a pretty good one. If someone were in one of the subgroups, the safety margin falls by half and the drug interactions theoretically MIGHT have an effect if they were also SUSCEPTIBLE. This requires a triple whammy to occur: interacting drugs, bad metabolizing of the drug, and .. susceptible to the side effect. So, not very likely.

However, you just wouldn't start with taking more than one drug when one drug would likely work. If it didn't work, you would go with A DIFFERENT DRUG. the standard way we handle these things fits with very sophisticated systems analysis... even though doctors are not aware of it.

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