Relationship between carbamazepine concentrations in plasma and saliva in man as determined by liquid chromatography

The concentration of carbamazepine in plasma and saliva was determined in 7 subjects receiving carbamazepine. Plasma and saliva samples were assayed was an excellent linear relationship between carbamazepine concentrations in saliva and plasma (r = 0.991, p less than 0.001) over a plasma concentration range of 0.2--8.0 microgram/ml. The saliva/plasma ratio for carbamazepine was 0.26 +/- 0.02 (S.D.). Since carbamazepine binding to plasma proteins is in the order of 75%, the saliva concentration seems to reflect the concentration of the free drug in plasma. There is very little intrasubject and intersubject variation in the concentration ratio of carbamazepine. This study demonstrates that carbamazepine determination in saliva is a convenient method for optimizing blood levels of patients as well as for the study of pharmacokinetic properties.