A High Plasma Lamotrigine Concentration at Week 2 as a Risk Factor for Lamotrigine-Related Rash

Reportedly, a high plasma concentration of lamotrigine plays a role in the development of lamotrigine-related rash. The relationship between plasma concentrations of lamotrigine at week 2 and the lamotrigine-related rash was prospectively studied in 84 patients (22 males and 62 females) with treatment-resistant depressive disorder during an 8-week treatment of lamotrigine augmentation.

Eighty-four depressed patients with an insufficient response to at least 3 psychotropics, including antidepressants, mood stabilizers, and atypical antipsychotics, were included. The diagnoses were major depressive disorder (n = 39), bipolar I disorder (n = 10), and bipolar II disorder (n = 35). The final doses of lamotrigine were 100 mg/d for 57 subjects who were not taking valproate and 75 mg/d for 27 subjects taking valproate. Blood sampling was performed at week 2. Lamotrigine plasma concentrations were measured using high-performance liquid chromatography. The development of lamotrigine-related rash was assessed during the 8-week treatment.

Six females developed lamotrigine-related rash. The mean plasma lamotrigine concentrations at week 2 were significantly (P = 0.009) higher in the rash group (4.81 ± 1.23 μmol/L) than in the nonrash group (3.35 ± 1.39 μmol/L). Receiver-operating characteristic analysis indicated that a plasma lamotrigine concentration of 4.38 μmol/L or greater at week 2 was significantly (P < 0.0001) predictive of lamotrigine-related rash. The proportion of patients with a lamotrigine concentration of 4.38 μmol/L or greater was significantly divided by the cutoff point into the rash group and the nonrash group (5/1 versus 13/65, P = 0.001).

This study suggests that a high plasma lamotrigine concentration during week 2 is a risk factor for lamotrigine-related rash and a plasma lamotrigine concentration of 4.38 μmol/L may be a considered a threshold for rash in treatment-resistant depressive disorder.