Stability of salivary concentrations of the newer antiepileptic drugs in the postal system.

Saliva antiepileptic drug (AED) concentrations strongly correlate with serum concentrations. Saliva collection is painless and noninvasive, and untrained personnel can easily be taught the collection process. Remote patients could mail saliva samples to a laboratory for monitoring, and samples could be obtained in the immediate postictal state to provide a "real-time" concentration. The objectives of this study were to assess the stability of saliva lamotrigine (LMT), levetiracetam (LEV), oxcarbazepine (OXC), topiramate (TPM), and zonsiamide (ZNS) concentrations sent through the United States Postal Service (USPS) and to quantify the amount of time needed for patients and the USPS to return samples to clinic. Saliva samples were obtained from patients currently taking 1 of the targeted AEDs. Samples were split into 2 storage vials. One sample was sealed in an addressed envelope, which the patient mailed from home, whereas the other sample was frozen immediately. Postmark date and day returned were collected for mailed samples. Saliva concentrations were determined using HPLC. Wilcoxon rank sum tests were used to compare the immediately-frozen and mailed sample means. Correlations were determined by the Spearman test. Thirty-seven patients were enrolled in the study. The median time between collection and postmark was 1 day (range 0-6 days); and between collection and receipt was 4 days (range 1-160 days). The mean concentrations for mailed and immediately frozen samples were similar for each AED (P > 0.15). Spearman rank order correlations between mailed and immediately frozen aliquots were strong (LMT rs = 1, LEV rs = 1, OXC rs = 0.964, TPM rs = 0.90, and ZNS rs = 1). Saliva samples mailed by patients maintain stability and can be returned in a reasonable length of time. Further studies are needed to assess patient/caretaker capability of obtaining an adequate sample.