The basis for this broader spectrum of activity of lamotrigine is unknown, but could relate to actions of the drug on voltage-gated calcium channels. Lamotrigine blocks T-type calcium channels weakly, if at all. However, it does inhibit native and recombinant high voltage–gated calcium channels (N- and P/Q/R-types) at therapeutic concentrations. Whether this activity on calcium channels accounts for lamotrigine's broader clinical spectrum of activity in comparison with phenytoin and carbamazepine remains to be determined.
