Does Topamax become toxic after the expiration date?

I used to take Topamax for miagrains. I stopped taking them for a lengthy period of time as my insurance was cancelled and it is a very expensive perscription. I recently found a bottle of topamax stored in a drawer in my home, and know it has been kept in a cool enviornment. However, it is a rather old perscription and has been expired for some time. I know that you are not advised to take medication after the expiration date, but my ONLY question is: Does Topamax become toxic after the expiration date? I realize it could possible not have its FULL effects, but I need to make sure it's ingredients do not become toxic as some medications do over time.

Please help! I can not afford a new prescription but the miagrains have become unbearable and this is the ONLY medication that has worked for long term preventative treatment.