Can Antibiotics Interact With Birth Control?

Hi,

My girlfriend and i have been dating for 3 months. Last week she had her period and she was having problems. She went to the doctor and gave her medicine for it. She also have taking birth control but stopped 3 days ago and then started taking the medicine. We had intercourse tonight like 4 times. After she said i think the medicine is antibiotics. What are the chances she is pregnant?