Effect of Genetic Polymorphisms of ABCB1, ABCG2, and SLC22A1 on the Steady-State Plasma Concentrations of Lamotrigine in Treatment-Resistant Depressed Patients Treated With Lamotrigine Augmentation Therapy.

Objectives: The authors have demonstrated that a plasma lamotrigine concentration of 12.7 μmol/L may be a threshold for a good therapeutic response to lamotrigine augmentation therapy in treatment-resistant depressed patients. Lamotrigine is a substrate of P-glycoprotein, breast cancer resistant protein and organic cation transporter 1, which are encoded by ABCB1 , ABCG2 , and SLC22A1 , respectively. There have been several polymorphisms that affect its function. The present study investigated the relationship between these polymorphisms and the steady-state plasma concentrations (Css) of lamotrigine in treatment-resistant depressed patients receiving lamotrigine as augmentation therapy.
Methods: One hundred twenty-nine treatment-resistant depressed patients were included in this study. Treatment resistance is defined as lack of therapeutic response to at least 3 psychotropics despite adequate doses and duration. Their diagnoses were as follows: major depressive disorder (n = 58), bipolar II disorder (n = 52), and bipolar I disorder (n = 19). Lamotrigine augmentation therapy for 8 weeks was conducted. The final lamotrigine doses were 75 mg/d for 39 patients with valproate and 100 mg/d for 90 without it. Blood was sampled at 8:00 am after the 8th week of treatment. Plasma lamotrigine levels were quantified by using LC/MS/MS. The polymorphisms of ABCB1 1236C>T, 2677G>T/A, 3435C>T, ABCG2 421C>A, and SLC22A1 1222G>A were detected by polymerase chain reaction analyses.
Results: No significant relationships were observed between these polymorphisms and the Css of lamotrigine in the patients with or without valproate.
Conclusions: The present study suggests that these genetic polymorphisms do not play a role in controlling the Css of lamotrigine in treatment-resistant depressed patients treated with lamotrigine augmentation therapy.
Competing Interests: Conflicts of Interest and Sources of Funding: K. Mihara has received honoraria from GlaxoSmithKline and Otsuka. A. Nakamura has received honoraria from Dainippon Sumitomo Pharma, Otsuka, and Pfizer. T. Kondo has received honoraria from Eli Lilly, GlaxoSmithKline, and Otsuka. The other authors declare no conflict of interest.
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