Prediction of an Optimal Dose of Lamotrigine for Augmentation Therapy in Treatment-Resistant Depressive Disorder From Plasma Lamotrigine Concentration at Week 2

Abstract

The authors have previously shown that an early therapeutic response to lamotrigine augmentation therapy is dependent on its plasma concentration and that a plasma lamotrigine concentration of 12.7 μmol/L may be a threshold for a good therapeutic response in treatment-resistant depressive disorder. The present study investigated whether or not an optimal dose of lamotrigine could be predicted from plasma lamotrigine concentration at week 2. The subjects were 37 depressed patients who had already shown insufficient response to at least 3 psychotropics including antidepressants, mood stabilizers, and atypical antipsychotics. The diagnoses were major depressive disorder (n = 15), bipolar I disorder (n = 6), and bipolar II disorder (n = 16). They received augmentation therapy with lamotrigine for 8 weeks. The final doses of lamotrigine were 100 mg/d for 16 subjects who were not taking valproate and 75 mg/d for 21 subjects taking valproate, respectively. Blood sampling was performed at weeks 2 and 8. Plasma concentrations of lamotrigine were measured by high-performance liquid chromatography. There were significant linear relationships between the plasma lamotrigine concentrations at week 2 (x) and those at week 8 (y) for subjects who were not taking valproate (P < 0.01) and those taking valproate (P < 0.01). Regression equations were y = 2.032x + 2.549 for the former and y = 3.599x + 5.752 for the latter, respectively. Based on the equations, a nomogram to estimate an optimal dose of lamotrigine could be calculated. The present study suggests that an optimal dose of lamotrigine for augmentation therapy in treatment-resistant depressive disorder can be predicted from a plasma lamotrigine concentration at week 2.