Pancreatic cancer and/or 5FU treatment

Hi All, new here and completely overwhelmed. My dad (62) is a 2 year survivor of PC who has been on gemzar (gemcidabine) for about a year and a half. His onc just gave us the news that he seems to have stopped responding to the gem and wants to change to the 5FU pump. Any input on what we are looking at side-effect wise? Not to mention seeing him wither away from 230lbs to 147lbs...I HAAAAAAAAATE this disease.....
Thank you so much for being here....
Brandee