Saliva and serum concentration of lamotrigine in patients with epilepsy

The authors examined the interindividual correlation between saliva and serum concentrations of lamotrigine (LTG) and the relationship between LTG concentration in saliva and the free LTG concentration in serum in 40 patients with epilepsy, aged 16 to 73 years, receiving stable doses of LTG and comedication. Saliva was collected before and after stimulation of salivary flow. The free LTG fraction was determined by equilibrium dialysis and ultrafiltration. Drug analysis was performed by high-performance liquid chromatography. The correlation between LTG daily dose and serum concentration was weak but significant (r = 0.47). There was high correlation between LTG concentration in serum and unstimulated (r = 0.85) or stimulated (r = 0.94) saliva, and between total LTG concentration in serum and the free LTG fraction as determined by ultrafiltration (r = 0.95) and equilibrium dialysis (r = 0.93). Lamotrigine concentration in stimulated saliva was significantly correlated to the free LTG fraction. Protein binding of LTG calculated from concentration in stimulated saliva, as determined by ultrafiltration and equilibrium dialysis, was 51.8% +/- 13.03%, 68.05% +/- 7.59%, and 58.72% +/- 7.68% (mean +/- standard deviation) respectively. The differences between the three methods were significant. The authors conclude that saliva sampling may be a useful alternative to blood tests for monitoring LTG treatment.