The infusion center will ask you a few questions. If you report anything in response to those questions, they will call your neurologist and ask him for his approval or disapproval in response to your answers. You may end up waiting hours until he calls them back but they will not give you the infusion until he responds. If he feels that the infusion should be withheld, you don't get it, period. Here's more info and the list of questions:
http://www.tysabri.com/tysbProject/t...ng-program.xml

I am careful to report any new or unusual symptoms to my neurologist when they occur and last more than 24 hours, as he has instructed me to do, so he knows about anything that may be going on before I go for the infusion. For some it is 48 hours, but my neuro is watching me pretty closely after 48 infusions, so it's 24 hours for me.

I haven't been refused an infusion yet. I skipped one since May 2007 because I was laying in a hospital bed looking up at all the bags hanging on the pole after an emergency appendectomy and feeling like i was going to vomit every 5 minutes, despite taking Zofran. I decided on my own to skip that infusion, with the blessing of my neurologist. He said it was up to me but he had no objection to me having the infusion or not having it, and said that the antibiotics I was on would not affect the infusion process at all, nor have any adverse effects on me.

When you get sick, you treat the illness. When I had a UTI it was treated. I had an impacted wisdom tooth, it was treated. I had salmonella, it was treated. If you have a relapse, it can be treated with steroids.

It's the long term therapy (pulse therapy) with steroids that is not allowed. You may not be allowed to have infusion if you are on chemotherapy for cancer treatment. You will not get your infusion if you have taken any immunosuppressants- but wouldn't your neurologist know about them anyway if you are reporting as you are supposed to do?