If you were my patient, I would advise you that if you take your pill exactly as directed you should be OK. If you are really concerned you could use condoms as a back up, but this is probably not necessary.
I would talk to your dr that prescribed you topamax I'm on it and I know that if I want to take any types of medicine. .. over the counter or otherwise its a good idea to just run it past him. He also has me taking folic acid just incase I do become pregnant. ... even though I have no intention of ever having children. .. because it reduces the risk of fetal abnormalities