I am currently in week 2 of 4 weeks of Bactrim. I missed one workout due to the illness and then subbed in Pettit for a few days. First hard day back and I say I was 5-10 watts off but I put this down to the illness more than the antibiotics, but it is impossible to say if it is illness, antibiotics, training interruption, mentality or regular variation. I feel totally fine and was able to complete 2 of the 3 hard workouts this week, will report back if I can see any impact going forward. Currently I am at the end of specialty so maybe the decreased volume covers up some of the potential impact of the antibiotics.