Saliva and Plasma Monohydroxycarbamazepine Concentrations in Pediatric Patients With Epilepsy

Monohydroxycarbamazepine (MHD, 10-hydroxy-carbamazepine) is the main active metabolite of oxcarbazepine (OXC). The present study aims to investigate the relationship between plasma and saliva concentrations of MHD in Chinese children with epilepsy.

Plasma and saliva samples were collected and MHD levels were measured by high-performance liquid chromatography system. Linear regression analysis was conducted between the dose of OXC and saliva concentrations, between the dose of OXC and plasma concentrations, and between the saliva concentrations and plasma concentrations. Student's t-test was used for unpaired data. A one-way analysis of variance was used for analyzing co-medication in subgroups of patients.

A total of 58 blood samples and 58 saliva samples were obtained from 52 pediatric epileptic patients, with a median age of 5.67 years (0.58-15 years, 23 males and 29 females). There was an apparent positive correlation between the plasma and saliva MHD concentrations [Y = 0.77x - 0.85 (n = 58), R = 0.908, P < 0.01]. MHD plasma and saliva concentrations were positively correlated to daily drug dose (r = 0.461 and 0.417; P < 0.01 respectively). The saliva/plasma MHD ratio was around 0.71 and had no significant difference with age, gender, and combined medications. When data were analyzed for subgroups (one group taking OXC as monotherapy, the second group taking OXC in add-on with non-enzyme-inducing antiepileptic drugs, and the third group taking OXC in add-on with hepatic-enzyme-inducing antiepileptic drugs or moderate inducers), no significant difference was found between plasma and saliva MHD concentrations in all the above 3 groups.

High correlation between plasma and saliva MHD levels supported the use of saliva as an alternative to plasma for OXC monitoring in children with epilepsy.