Possible roles for frequent salivary antiepileptic drug monitoring in the management of epilepsy.

Salivary levels of phenytoin, phenobarbitone, carbamazepine and carbamazepine-epoxide correlate with the simultaneous plasma water levels of these substances, after correcting for the effects of pH differences between saliva and plasma in the case of phenobarbitone. Saliva is easy and painless to collect, and salivary levels of the drugs are conveniently measured. Frequent (often daily) monitoring of pre-dose morning anticonvulsant drug concentrations in saliva over periods of weeks or months in 3 groups of epileptic subjects showed that (i) in some but not all poorly controlled epileptic patients seizures tended to occur on days when salivary anticonvulsant levels were lower than on non-seizure days, (ii) in such subjects it was possible to estimate an anticipated optimal drug concentration and dose to minimize seizure activity from the plot of seizure frequency against drug concentrations, (iii) in women with 'catamenial' epilepsy, salivary anticonvulsant levels were lower on perimenstrual days than at mid-cycle in half of the subjects studied, and (iv) in pregnant epileptic women the time course of the change in drug levels relative to dose could be followed more closely throughout pregnancy and the post-natal period than was practicable when using blood level measurements. Frequent measurement of salivary anticonvulsant concentrations appears a promising and inexpensive adjunct to the investigation and management of certain problem areas in epilepsy.