Correlation of Lamotrigine Concentrations between Serum and Saliva

Study Objective. To compare the relationship between serum and salivary concentrations of lamotrigine in pediatric and adult epilepsy populations. Design. Paired-sample pharmacokinetic study. Setting. University neurology clinic. Patients. Thirty-seven patients with epilepsy, aged 2-60 years, who were taking lamotrigine and whose physicians had ordered a lamotrigine serum concentration. Measurements and Main Results. Patients spit a minimum of 0.25 ml into a cup to provide saliva samples. Blood samples were obtained by phlebotomy. Serum and salivary lamotrigine concentrations were determined by high-performance liquid chromatography. Linear regression analysis was used to evaluate correlations. Six patients' results were omitted due to the lack of a serum or saliva specimen or clearly erroneous results, leaving 31 patients for analysis. There was a strong correlation between the serum results reported by two reference laboratories (coefficient of correlation [r] = 0.988). The correlations between salivary and serum lamotrigine concentrations were similar for reference laboratory A (r = 0.81) and reference laboratory B (r = 0.84). Saliva:serum concentration ratios ranged from 0.41-1.26 (mean ± SD 0.62 ± 0.19) for reference laboratory A and from 0.40-1.19 ((mean ± SD 0.64 ± 0.18) for reference laboratory B. Conclusion. There is a good correlation between salivary and serum concentrations for lamotrigine. However, there is wide interpatient variability in the saliva:serum ratio. The data suggest that salivary monitoring may play a role in the monitoring of lamotrigine for adult and pediatric patients.