Abstracts

Using saliva in place of serum for therapeutic monitoring has several advantages: increased ease of collection; deceased risk of infection; and decreased discomfort. This option becomes particularly important for infants and children, patients with limited physical mobility, persons who cannot drive, and for patients in rural or remote settings with limited access to health care facilities. The purpose of this study is to determine the correlation between saliva and serum concentrations of 10-11-dihydro-10-hydroxy-carbamazepine (MHD), the active metabolite of oxcarbazepine, and to assess the feasibility of salivary MHD determination for routine therapeutic drug monitoring.
Patients with epilepsy who were taking oxcarbazepine and attended the neurology clinic at the University of Kentucky Medical Center (UKMC) were eligible for this study. IRB approval was obtained. A minimum of 0.25 mL of saliva was collected into a microtube. Blood was collected by a phlebotomist. Serum was sent for routine MHD analysis at UKMC (reference lab A). Saliva and serum specimens were stored at -20[deg] C until MHD analysis at a reference laboratory at Cincinnati Children[apos]s Hospital Medical Center (reference lab B). MHD concentrations were determined by validated HPLC methods at both reference laboratories. Results are expressed as mean [plusmn] SD.
Patient ages ranged from 3 to 51 years (22.5 [plusmn] 14.0 y). High patient and family acceptance of saliva collection was observed. Serum results from reference lab A (n = 20) ranged from 7 to 48 [micro]g/mL (24.8 [plusmn] 11.8 [micro]g/mL). Serum results from reference lab B (n = 20) ranged from 5.8 [micro]g/mL to 48.4 [micro]g/mL (25.9 [plusmn] 11.8 [micro]g/mL). Saliva concentrations (n = 20) ranged from 4.7 to 42.6 [micro]g/mL (23.9 [plusmn] 10.4 [micro]g/mL). There was a strong correlation between the serum results reported by reference laboratories A and B (r = 0.970). The saliva-to-serum concentration ratios from reference lab A ranged from 0.67 to 1.23 (0.98 [plusmn] 0.14), and there was a strong correlation between saliva and serum values ( r = 0.951). Reference lab B saliva-to-serum concentration ratios ranged from 0.72 to 1.13 (0.93 [plusmn] 0.12), and a similar strong positive correlation was evident ( r = 0.960).
Saliva collection is simple and well-tolerated by children and adults. Results indicate that the mean concentration of MHD in saliva is approximately 95% of the serum concentration, although some interpatient variability is apparent. Results from 2 reference laboratories indicate a strong correlation between saliva and serum MHD concentrations. These study shows that saliva MHD concentration monitoring is feasible, and may provide a useful alternative to serum testing for certain patients. Further validation is needed to prove reliability and clinical usefulness.