BCG has long-lasting efficacy. Dr. Ashish Kamat of MD Andersons Cancer Center in Texas had mentioned by showing a study that though the complete response rate (no recurrence and no progression) was 55% for CIS after the initial 6 weeks induction course, it increased to 84% after the first 3 weeks maintenance course. I watched a case study video by three urologists recently. In the video, Dr. Peter Black of the University of British Columbia mentioned that for CIS only patient, he does not even do a cystoscopy after the 6 weeks BCG and wait till after the completion of the first 3 weeks maintenance course as he recognizes the longevity of BCG effectiveness.
I am a bit concerned about you are scheduled for another 6 weeks BCG treatment, as the standard protocol for BCG treatment for CIS is 6 weeks induction course and followed by 3 weeks of maintenance at 3 months, 6 months, 12 months, 18 months, 24 months, 30 months. Dr.Kamat is not recommending 6 weeks followed by 6 weeks of treatment.
Below is the link to the video by Dr. Kamat. He starts talking about BCG treatment at 8:30
Best
I would not do anything except drinking lots of water/liquid after BCG as Sara suggested to lessen the side effect. It is a good idea to avoid coffee, soda, spicy food, and acid food to prevent irritation of the bladder, which will be exposed to urine by BCG bacteria breaks the protective lining of the bladder. This suggestion was given by a doctor for patients who have interstitial cystitis due to UTI/Bacteria infection to the lining of the bladder. BCG is live weakened tuberculosis causing bacteria. So, over 30% of BCG patients experience cystitis of the bladder (urgency, frequency, and pain).