You can count on it being ineffective for about two weeks or so after you finish your antibiotics. Don't take risks. Have him wear a condom or abstain. I have several friends who were only conceived because their mothers were on antibiotics at the time.
Yes. Honestly, if you're not trying for a baby, it's best to just assume that your pills will be completely nonfunctional. You can chance is and assume you'll be ok because many people ovulate later than the first week after their period, but personally I think condoms are the way to go. It's not worth the stress in my opinion.