Salivary levels of anticonvulsants: a practical approach to drug monitoring.

Phenobarbital, phenytoin, carbamazepine, primidone, and ethosuximide were measured in saliva and plasma obtained simultaneoulsy from 115 patients. A method to correct for the effect of salivary pH on phenobarbital concentration of saliva was developed. Salivary concentrations of these drugs were found to be equivalent to the plasma free drug and to correlate closely with the total plasma levels. Expressed as percent of total plasma drug, the salivary (S) and plasma free (P) concentrations were: phenytoin, S 11.1 +/- 2.0 percent (mean +/- SD), P 10.1 +/- 2.4 percent (r = 0.97); carbamazepine, S 26.0 +/- 2.4 percent, P 25.9 +/- 3.4 percent (r = 0.97); phenobarbital, S 43.1 +/- 5.2 percent, P 40.8 +/- 7.9 percent (r = 0.91); primidone, S 75.4 +/- 24.9 percent, P 66.4 +/- 8.8 percent (r = 0.76). Ethosuximide was not bound by plasma proteins, and its plasma and salivary levels were equal.