it depends on where in your cycle you are and what antibiotic you are taking. not all antibiotics affect birth control pills. a general rule of thumb is to use an alternative method of birth control for the course of the antibiotic usage and for seven days after you stop. but it really would depend on your individual situation. you should talk to your gynecologist or pharmacist about what you should do.
i know my antibiotic reduces the effectiveness of my birth control pills. how long should i continue a back-up method?