Comparative daily profiles with different preparations of lamotrigine: a pilot investigation.

Comparative pharmacokinetic data obtained with different preparations of lamotrigine (LTG) are reported for the first time. Nine outpatients reporting problems attributed to shifts in the preparation of LTG used were admitted to hospital. Patients were treated with proprietary LTG for at least 2 weeks prior to admission. Daily profiles (DPs) spanning 24 hours were obtained by blood sampling at 3- or 4-hour intervals on Day 3 after admission. A second DP was obtained under similar conditions after generic LTG therapy for at least 7 days. LTG concentrations were determined by HPLC, and DPs were generated to compare pharmacokinetic parameters. In five of nine patients, parameters deviated beyond +/-10%. Even with the narrower bioequivalence requirements for mandatory substitution in Denmark, there are some patients who experienced serious clinical consequences (relapse in a seizure-free patient, status epilepticus, epidural hematoma due to ataxia with falls) in association with a change in preparation, and significant corresponding alterations in plasma levels could be demonstrated by comparative pharmacokinetic testing.