If i took plan b yesterday and started antibiotics (biaxin) today, will that reduce the effectiveness of the plan b?

"Plan B": Some antibiotics can interfere with absorption of oral birth control (Plan B for example), but not enough to reduce the hormonal effect on the uterine lining, which can prevent some pregnancies by inhibition of implantation of a fertilized egg. Plan B is not always effective, however, so if your period is delayed, obtain a serum HCG test to be certain of pregnancy.