LAMOTRIGINE AND PHENOBARBITAL
Phenobarbital has been associated with reduced lamotrigine serum levels (reduction of about 50% in one study). Lamotrigine does not appear to affect phenobarbital or primidone levels.
Phenobarbital induces the metabolism of lamotrigine, and the recommended starting dose and long-term maintenance dose of lamotrigine in patients already taking phenobarbital or primidone is twice that of patients receiving lamotrigine monotherapy. However, note that if they are also taking valproate in addition to phenobarbital, the lamotrigine dose should be reduced.
Phenobarbital induces the metabolism of lamotrigine, and the recommended starting dose and long-term maintenance dose of lamotrigine in patients already taking phenobarbital or primidone is twice that of patients receiving lamotrigine monotherapy. However, note that if they are also taking valproate in addition to phenobarbital, the lamotrigine dose should be reduced.