Lamictal really isn't as effective for mania as other mood stabilizers, it is better for the depressive end of Bipolar, in fact Lamictal caused my brother's mania to escalate this summer, which his pdoc weaned him off after a few months of being on it, once my brother went to the hospital, they started him on Tegratol and Zyprexa, so far my sister-in-law claims he's tame enough to live with again.
Anti-depressants are usually a "no no" for those with Bipolar with tendency of mania, cause the AD's can actually spark and fuel mania. I'd say the Lexapro and Lamictal are probably just fueling your husband's mania.
If at all possible,get a 2nd opinion from another pdoc, or confront his about possible alternatives, such as Tegratol,Depakote,etc. also he may need something combined, like an anti-psychotic,tranquilizer and/or an anti-anxiety.
Just seems odd his pdoc doesn't see the present meds not mixing well for someone with Bipolar mania, cause it's almost a given that Lexapro and Lamictal will increase mania in those with severe Bipolar-I.
Maybe the Lamictal should be considered for the depressive end, and discontinue the Lexapro, and add a med in place for mania.
I'm not a pdoc, but just was thinking of what may be the culprit(s) here, after seeing what my brother and sister-in-law just went through, as well as others.
There are effective meds, it's just getting at the right combo and dosages that takes time and patience.
A reputable pdoc who is updated on meds, is also a huge factor in obtaining a balance.
My DX is Bipolar-II Mild, never really ever had mania, just deep depessions that anti-depressants stopped working on.
I'm on the lowest therapeutic dose and have had much sucess with it, now I'm just dealing with melancholia due to loss of loved ones and good old days. Entering menopause (waning hormones) plus thyroid disease is not helping me either, but I'll survive I guess, even my pdoc feels that is a major thing right now,menopause can suck.
I wish you lots of luck with this, and be kind to yourself.