Here's a word to the wise: if ever you have a question about compatibility, check a current IV drug book (every facility should have one handy) and/or consult your on-site pharmacist. This is the best way to prevent incidents like this one from happening.......don't rely on the word of another nurse, or even an MD---you need to take the time to check it yourself. Even experienced nurses have to do this from time to time, as it's impossible to keep up with all the changes in pharmacology and we don't usually have instant access to information about them.
As for TPN, it's safe to assume that nothing (other than lipids) can be infused with it, and even then you connect the line containing the lipids below
the filter to avoid clogging it up. It sounds to me like this patient's doctor should consider a different central vascular access device, particularly if peripheral IV access is difficult and he's in the hospital frequently, but that's just my humble opinion.
At any rate, you've learned a valuable lesson here, and you'll never make the same kind of mistake again, so be gentle with yourself.
Good luck to you!