Yes, you can stop a blood transfusion. As long as you get the transfusion into the pt within the 4 hr period, then it's fine. While I *have* kinked the line above the port and flushed, put in med, flushed again, I think it's safer to stop the transfusion, disconnect, flush, administer, flush, reconnect and re-start.
Whether to hold the med until after its done depends on the med for me. What's it for? Do they need it NOW? What would change if it were held until the transfusion is done?
A PRN pain med? I try to medicate before transfusion, but if breakthrough pain happens, then there you are. Do I make the pt wait 2 more hours? No, that would be mean.
I've had a peripheral line infiltrate during a transfusion. What to do? Well, you stop the transfusion, start a new line and restart.
However, it is best to follow your facilities policies.