How is pain treated while you are taking methadone?

What pain? Methadone is the ultimate anti-inflammatory; so any breakthrough pain should be addressed with your physician. I suppose tylenol (acetaminophen) would help, but you should run any new symptoms by your physician before taking any new medication!
More stuff. If Methadone for pain, the dose can be spread out, ie 3 times a day, or imcreased. If Methadone for addiction i generally dose the daily dose 3xday and add a second opioid like oxycodone. I also maximize non-opioids, as opioids are less effective when on them chronically. Gabapentin/lyrica, celebrex/advil, tylenol, (acetaminophen) IV lidocaine, ketamine are choices. For surgery i prefer nerve blocks/epidural.