Correlation of saliva and serum free valproic acid concentrations in persons with epilepsy

PURPOSE Therapeutic drug monitoring (TDM) of antiepileptic drugs (AEDs) in serum is frequently used in clinical settings however saliva could be an alternative to measure free concentration of drugs. In the present study, we observed the possible correlation of VPA concentration between serum and saliva in persons with epilepsy (PWE). METHODS A total of 59 paired serum and saliva samples were assayed from 65 consecutive PWE (51 males and 14 females; age range 9-65 years). Patients were subjected to either VPA monotherapy or its combination with other AEDs for at least three months. Steady state trough concentration of unbound VPA drug was quantified using HPLC. The correlation between serum and saliva free VPA concentration was evaluated. RESULTS Out of 65 patients, 27 were on monotherapy of VPA and 38 were on VPA with other antiepileptic drugs. Saliva VPA concentration significantly correlated with serum free VPA concentration (p<0.05). Poor correlation was observed between serum and saliva VPA concentration with the daily dose (p>0.05) respectively. CONCLUSIONS Our study reveals that serum and saliva VPA concentrations are significantly associated in PWE. These associations may facilitate monitoring and evaluation of VPA levels non-invasively for PWE.