I am currently getting #18 right now! It was nice to have the IV go in easily the first time. I had to delay a week because of a persistent UTI and I was in Mexico. Somehow this time around the delay didn't worry me like it did the time I was delayed a year ago due to a respiratory infection. I wonder what made the docs decide that every 4 weeks is better than say every 5 or 6 weeks? The weird thing is I can't tell a difference in how I feel. If anything I seemed to have a little more extra energy at the end and before the next infusion. I'm starting to figure out that the Tysabri wipes me out for a good 7-10 days. I feel so drowsy all the time during those days and my brain is a little foggy or slower.