Objective: Antiepileptic drugs (AED) are administered either singly or in combination with other drugs. Their pharmacokinetics is influenced by drug-drug interaction & inter-individual variations. Lamotrigine (LTG) is a second order AED with similar constraints.
Hence studying the relationship between lamotrigine dosage and plasma concentration was undertaken to offer assistance in therapeutic regimen.
Methods: Pre-dose blood samples for lamotrigine estimation were obtained from 267 patients (138adults & 127children) including 2 pregnant women. Lamotrigine estimation was done by high performance liquid chromatography.
Results: In our study more children (73%) than adults (34%) were on adjunctive therapy with inhibitors (valproic acid) or inducers (phenytoin, carbamazepine, oxcarbamazepine). Irrespective of co-therapy lamotrigine level within therapeutic range with an optimal seizure control was obtained only in 76% of children and 65% adults. In case of polytherapy with valproic acid, when lamotrigine dose was maintained similar or lower than monotherapy, lamotrigine levels were 105% and 65% higher in adults and children respectively. Increased volume as observed in pregnancy had a remarkable influence on lamotrigine level. An increase in drug dose with an increase in gestation was required in both pregnant women to maintain the plasma level.
Conclusion: Inter-individual variations, co-medications and clinical conditions like pregnancy influence plasma lamotrigine level. Thus, drug monitoring is essential to obtain therapeutic efficacy for individual dose optimization
