Took 3 days antibiotics (Pen Rafa) and had unprotected sex while taking Yaz, (drospirenone and ethinyl estradiol) first week of pills, what are the chances of pregnancy?
Very Very low... Penicillin doesn't change the effectiveness of Yaz (drospirenone and ethinyl estradiol) (or other birth-control pills.) If you are taking the Yaz (drospirenone and ethinyl estradiol) correctly and not missing days, your chances of pregnancy are the same as if you didn't take penicillin: Very very low. (Near zero) Best wishes!