Therapeutic drug monitoring (TDM) of gabapentin (GPT) and lamotrigine (LTG) was performed in epileptic patients in order to verify a possible relationship between their serum concentrations and clinical effect and eventual kinetic interactions with carbamazepine (CBZ) and valproate (VA). Having acquired their informed consent 34 epileptic patients, suffering from partial complex seizures and resistant to conventional anticonvulsants, were assigned to GPT or LTG treatment groups. A poor relationship was observed between dose (mg/kg b.w.) and GPT or LTG serum levels. Patients contemporarily treated with VA presented the highest LTG serum levels; those with CBZ showed an inverse relationship between CBZ serum concentrations and daily LTG doses whereas CBZ-epoxide ones appared directily correlated. Two patients in each treatment group had an about complete control of seizures. Their serum concentrations were : GPT = 6.61 and 2.8 μg/ml; LTG = 4.65 and 3.1 μg/ml. A 50-75% reduction of number of sezures was observed in other 5 patients of each group. In 2 patients with GPT and 5 patients with LTG the efficacy was lower than 50%. No effect was observed in 4 patients with GPT and in 8 patients with LTG. The serum levels ranged from 1.9 to 7.5 μg/ml in the GPT group and from 2.3 to 10.7 μg/ml in the LTG group. On the basis of these date it mayn't be concluded that a therapeutic range of serum concentrations exists.
