I'm BP as well and was on lamictal throughout my entire pregnancy with dd & she was ebf for 6 months and then self weaned at 22 months when my milk dried up from this pregnancy. My current dose is 350mg a day... this baby will be bf as well when he is born.
These are the things I considered when researching - granted this was over 2 yrs ago now so I might be a bit foggy on some of the details... but here goes...
1. I looked at my dose and I calculated the RID (relative infant dose,) based on the info in Thomas Hale's book. BTW - I truly consider him the best source of info when it comes to the safety of medication and bf'ing. He is very pro bf'ing but will tell you if he has concerns about a drug.
2. There is some research info out there from when lamictal was being licensed & it was tested in children aged 2 & up. This is the info I don't recall exactly & I don't have time to look it up right now, but it gave a mg/kg dose that they used when testing it in the pediatric population and what range it had to be in to be considered therapeutic.
3. Steven's Johnson Syndrome is a rare side effect of lamictal & it's true that it does affect children more often than adults... however, starting at a very low dose with very slow dosage increases has been shown to decrease the incidence of developing SJS.
4. I know this doesn't apply to the OP, but if you're on it when pregnant, your baby is getting more lamictal in utero than he/she will get when bf'ing.
So in my case, when I did the calculations, my dd wasn't getting anywhere near a clinical dose when you look at the mg/kg ratio. I still monitored her closely the first few weeks after birth to make sure she didn't develop any strange rashes, but she had no problems.
Also, in regards to the folic acid - that concern is speculated to be more in regards to moms who take lamictal while pregnant... although the most recent #'s I have seen have shown that woman who do not have epilepsy and don't take lamictal at the same time as depakote do not have any higher risk of having a baby with spina bifida or other neural tube defects. These disorders are one's that develop in the 1st trimester, so this wouldn't be a concern with a 6 month old nursling.
Good luck with the decision... I know for me I did all the research before I got pregnant with dd and then again right before I delivered. Dd's dr. never had a problem with my meds - I was also on Paxil when I delivered...
But anyways, once I looked at the actual therapeutic dose ranges and realized that my dd wouldn't be getting within that range, I relaxed a lot.
Feel free to PM me if you have other questions, for me Lamictal has been an absolute life saver... it really helped me turn my life around and I've been on it for 6 yrs now. If you'd like I can also try & drum up the exact links that I used before. I know the info I got from the pediatric testing in clincical trials came from one of the technical write-ups that described the licensing process & groups of study population, effectiveness, etc.