I Have Colon Cancer Which Is Responding Very Well To

I have colon cancer which is responding very well to avastin and 5fu. Since I have had sinus infection for 5 weeks oncologist only gave me 5fu on Fri.. Avastin seemed to prevent Augmentin from getting it and I had bad reaction to bactrim. My sinus Doc put me on ceftin and I started today. How long before it works? Will it interact with 5fu. My 5fu pump comes off tomorrow. I had Almost 2 week break from from last bactrim which I took for 4 days and before that augmentin gor 14 days. Thank you