IV Dilantin infilitration

We have a patient who recieved a loading dose of IV dilantin on a Saturday and complained of swelling and redness 36 hours later. He had been recieving PO dilantin since the loading dose and also getting IV morphine approx q7h. Yesterday Monday the arm had increased in size, the redness was now the angry red, felt very hard. It looks like typical cellulitis and the gentleman is now on IV antibiotics. We are having a hard time believing that IV morphine would do this. It's not purple glove syndrome. Has anyone ever had experience with this? (the IV was an 18 gauge in the Antecube)