Vitamin B 1 should not be taken at the same time as the Antibiotics because it interferes with the absorption and effectiveness. All vitamin B complex supplements act in this way and should be taken at different times from the Antibiotics .
Strong Antibiotics , both natural and synthetic does destroy some of the valuable intestinal flora that produces B vitamins in your body (as many people with IBS from long term use of antibiotics may well know).
I would suggest using Vitamin B complex after Antibiotic treatment is over to compensate for the depletion.