Prophylactic antibiotics and the pill

There’s a thread in IMHO about birth control failure, and it got me to thinking about something I’ve wanted to know for a while.

I’m aware that having to take a full cycle of antibiotics can decrease the effectiveness of the pill. But does taking antibiotics for prophylaxis (in my case before a visit to the dentist) have the same effect? I guess what I’m saying is, how much do you have to take, and for how long, for it to interfere? If I take 2000 MG of amoxicyllin once, is it as bad from a contraceptive perspective as a full cycle for strep throat or some other bacterial infection?

While I’m at it I might as well ask somebody to clear up issue of how long you need to use back-up after you know there’s been a breach in the effectiveness of your BC.

First off, it’s not been established that “antibiotics” decrease the BCP’s effectiveness. Very few antibiotics actually have been demonstrated to have this effect. Rifampin is the only one that has solid documentation which shows a definite effect.

Anecdotal stories about women getting pregnant on the pill while taking other antibiotics like the penicillins, metronidazole, the cyclines (tetracycline, minocycline, doxycycline), the cephalosporins (keflex, etc), erythromycin, and INH are commonplace, but thus far studies done show no such effect.

Doesn’t mean that they don’t effect BCP effectiveness, just that it really hasn’t been demonstrated.

So there’s no real answer to your question. If you’re worried, use an additional method of birth control.

QtM, MD