What pain medicine taken while having a certain disease can make you die?

Question

I'm writing a story about two doctors who bond over the years, and I'm having a little trouble.

This patient is rushed in because he was in a severe car accident where the car door pinned his arm from the mid-bicept down was severed off. So, he's taking pain medicine to ease it.

He drifts in and out of consciousness and he has no immediate family, so not much is known about his background. What pain medicine and what disease could he have that when he takes the pain medicine, he reacts badly and dies?

Preferably looking for a disease that is found on a full body MRI.

Answer 1

liver disease?  

Answer 2

well he might have had an allergic reaction or something. and any medication can kill you if its taken in a high enough dose

Answer 3

If you're writing about doctors.. it might be a good idea to be one.

I'm not one but I'd assume that a patient would only receive medication after screening for any conditions that may complicate the situation.