Appropriateness of antiepileptic drug level monitoring.

OBJECTIVES

To develop explicit, reliable appropriateness criteria for antiepileptic drug level monitoring and to assess the appropriateness of monitoring in one tertiary care institution.

DESIGN

Appropriateness criteria derived from the literature and through expert opinion were used to evaluate a stratified random sample of antiepileptic drug level determinations obtained from chart review.

SETTING

Tertiary care center performing more than 10,000 antiepileptic drug level determinations per year.

PATIENTS

A total of 330 inpatients in whom antiepileptic drug levels were measured a total of 855 times.

METHODS

Drug levels were assessed at least 200 times for each of four antiepileptic drugs (phenytoin, carbamazepine, phenobarbital, and valproic acid).

MAIN OUTCOME MEASURES

The proportion of antiepileptic drug levels with an appropriate indication and, of those, the proportion sampled appropriately.

RESULTS

Overall, 27% (95% confidence interval, 24% to 30%) of levels had an appropriate indication. Interrater agreement for appropriateness was substantial (kappa = 0.61). There was no significant difference in the appropriateness rate among the four drugs (range, 25% to 29%). Of the 624 antiepileptic drug level determinations considered inappropriate (73%), only four (0.6%) were more than 20% higher than the upper limit of normal, and none of the four patients had clinical signs of drug toxicity. A median of six levels (range, one through 69) was determined per patient, and the median interval between level determinations was 24 hours. Of the 27% of level determinations with an appropriate indication, 51% were sampled correctly, resulting in an overall appropriateness rate of 14%.

CONCLUSIONS

Only 27% of antiepileptic drug level determinations had an appropriate indication, and half of these were not sampled correctly. Routine daily monitoring without pharmacological justification accounted for most of the inappropriate drug level determinations. Efforts to decrease inappropriate monitoring may result in substantial cost reductions without missing important clinical results.