I thought I'd post an update. Here is what I got back from a LLL leader:
Luckily I am reading this at work so I have the newest Hale (2006). It sounds like there are now more studies available showing no adverse effects so it is now an L3. Here's a quote, " Topamax has become increasingly popular due to its fewer adverse side effects. Due to the fact that the plasma levels found in breastfeeding infants were significantly less than in maternal plasma, the risk of using this product in breastfeeding mothers is probably acceptable. Close observation for sedation is advised." This is an "old" baby also and so baby is probably getting a little less milk than in the early months and better able to digest and move the drug out of his system.
Hope that helps.