The appropriateness of antiepileptic drug (AED) level monitoring was assessed in a tertiary care center performing more than 10,000 AED level determinations per year and reported from the Brigham and Women’s Hospital, Boston, MA. In a total of 330 inpatients with AED levels measured a total of 855 times, only 27% of levels had appropriate indications, and only half of these were sampled correctly as trough levels, resulting in an overall appropriate test rate of 14%. Indications were baseline, control levels after starting treatment or after steady state was achieved with a change of dose (13%), after a seizure relapse (8%), suspected drug toxicity (4%), presumed patient noncompliance (1%), and possible drug interaction (1%). The rate of determination was the same for all drugs (phenytoin, carbamazepine, phenobarbital, valproic acid). Of the 73% of levels considered inappropriate, three quarters had been obtained after starting or changing the drug regimen, frequently on a daily basis, and before achieving a steady state; 23 (3.7%) were above the therapeutic range and potentially toxic. The avoidance of inappropriate testing would have resulted in a saving of >$300,000. 
COMMENT. Appropriate indications for AED levels include: 1) seizure recurrence, 2) drug toxicity, 3) patient noncompliance. Blood should be drawn at time of steady state (6 days for phenytoin, 3 days for carbamazepine and valproic acid, and 20 days for phenobarbital), as a baseline, after change of dose, after addition of second drug, or after change in liver or gastrointestinal function. Except after seizure relapse or with suspected toxicity, trough levels should be obtained. More frequent AED level determinations may be indicated during pregnancy and labor, after surgery, and in infants and children. The authors of this study conclude that appropriate indications and timing of AED level determinations were not followed in 75% of patients in their tertiary care hospital. More careful adherence to appropriate monitoring indications would have resulted in cost reductions without significant risk of ineffective therapy or toxicity.