Lacosamide Concentration in Various Biological Matrices (Plasma, Saliva, and Hair) Does Not Correlate with Clinical...

Comparing drug concentrations in blood, saliva, and hair may provide important insights into pharmacokinetics. Salivary drug levels may serve as a substitute for blood concentrations, while drug content in hair can reflect long-term exposure and allow reconstruction of treatment history. The study investigated the relationship between lacosamide concentrations in plasma, saliva, and hair, the number of seizures during the previous 3 months, and treatment adherence.

An observational, retrospective study was conducted between 2020 and 2022 to evaluate the correlation between plasma, saliva, and hair lacosamide concentrations, seizure frequency in the preceding 3 months, and patient adherence. Lacosamide concentrations in plasma, saliva, and hair were determined using liquid chromatography-tandem mass spectrometry in the positive ionization mode. The study group consisted of patients with epilepsy treated at the Institute of Psychiatry and Neurology in Warsaw, Poland.

A total of 39 patients with epilepsy were included. Neither hair nor plasma lacosamide concentrations correlated with the number of seizures in the previous 3 months. Unexpectedly, patients who reported regular medication intake had significantly lower lacosamide concentrations in hair (8.1 ± 2.90 ng/mg) compared with those who did not adhere to fixed dosing times (43.00 ± 14.76 ng/mg). A strong correlation was observed between plasma and saliva lacosamide concentrations (r = 0.85, P < 0.05), indicating that saliva may serve as an effective alternative matrix for monitoring lacosamide levels.

Lacosamide concentrations in blood, saliva, or hair do not correlate with seizure frequency and are therefore not reliable markers of adherence. However, salivary lacosamide measurement may offer a practical alternative to plasma monitoring.