Appropriateness of serum level determinations of antiepileptic drugs

To assess the appropriateness of the determination of the serum levels of the antiepileptic drugs (AEDs) phenytoin, valproic acid and carbamazepine in inpatients of a tertiary care institution.

We performed a retrospective analysis of 602 AED serum level determinations. Appropriateness criteria regarding indication and timing were defined a priori using existing criteria from the literature. The main outcome measure was the proportion of serum levels with an appropriate indication and sampling time.

Of 602 levels assessed, 463 (77%; 95% confidence interval [95% CI], 74-80%) had an appropriate indication with a range of 68% to 84% for individual AEDs; overall, 65% (95% CI: 61-69%) met the criteria for appropriate timing. Combining the two criteria, 268 (48%; 95% CI: 44-52%) AED level measurements were assessed as appropriate. Of 139 (23%, 95% CI: 20-27%) levels assessed as having an inappropriate indication, the majority (77%) were performed for routine monitoring.

Less than half of all AED measurements met our criteria for appropriate AED level determinations. This creates unnecessary costs. Our data indicate the need for means to improve the rational use of AED serum level determination.