Abstract, published in Epilepsia
The assay of saliva samples provides a valuable alternative to the use of blood samples for therapeutic drug monitoring (TDM), at least for certain categories of patients. To determine the feasibility of using saliva sampling for the TDM of rufinamide, we compared rufinamide concentrations in paired samples of saliva and plasma collected from 26 patients with epilepsy at steady state. Also investigated were the relationships between plasma rufinamide concentrations and dose as well as the influence of “add-on” medications
Assay results in the two tested fluids correlated well, but concentrations in saliva were moderately lower than those in plasma. In eight patients evaluated at three different dose levels, plasma rufinamide concentrations increased linearly with increasing dose. However, patients receiving valproic acid (Depakote®) “add-on” medication had higher dose-normalized plasma rufinamide levels than patients taking “add-on” medications metabolized by a different enzyme than that for rufinamide.
Overall, these findings indicate that use of saliva represents a feasible option for the application of TDM in patients treated with rufinamide. Nevertheless, because rufinamide concentrations are lower in saliva than in plasma, a correction factor is needed if measurements made in saliva are used as a surrogate for plasma concentrations.