Table 2.

Uses of AED Blood Level Monitoring

Setting	Rationale	Applicable AEDs	Usual AED Modification
Assessing Complex Pharmacokinetics	Narrow therapeutic Index; complex metabolism	Phenytoin above 300 mg/day; Carbamazepine	Variable: adjust phenytoin by small doses; reduce carbamazepine
Initial Therapy	Document successful therapy	All	Serves as “baseline” for future comparison if seizure control deteriorates
During AED Conversions	Ensure sufficiently protective dosing of new AED, Evaluate drug interactions	All	Raise or lower doses
Therapeutic Failure	Exclude non-adherence/non-compliance “rule-In” Intractability	All transition to new therapy; reinforce compliance	Raise dose or transition to new drug
Pregnancy	Altered pharmacokinetics	All	Raise or lower dose
Liver/Renal Disease	Altered AED metabolism/clearance	All	Usually lower dose
Polypharmacy	Altered pharmacokinetics	Enzyme-inducing AEDs; Enzyme-inhibiting AEDs; Inducible AEDs	Lower doses of inducing AED; Lower doses of other AED; Raise inducible AED dose
Children/Adolescents	Increased AED Metabolism/Clearance	Most	Raise doses
Elderly	Decreased AED Metabolism/Clearance	Many	Lower doses