When are serum antiepileptic drug (AED) levels measured in the management of epilepsy?

Updated: May 30, 2019
  • Author: David Y Ko, MD; Chief Editor: Selim R Benbadis, MD  more...
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Judicious testing of serum levels of antiepileptic drugs (AEDs) may help to improve the care for patients with seizures and epilepsy. However, note that many new AEDs do not have readily obtainable or established levels. The following situations may be indications for obtaining serum AED levels:

  • Baseline measurements: After the seizures are controlled, the AED dose is then established, and the levels needed to achieve seizure-free effectiveness if there are expected changes in the levels, such as occurs with pregnancy, may be also be obtained

  • Toxicity and efficacy: The toxicity and efficacy of an AED is a clinical decision not based on levels per se but on how the patient is doing; an AED level may be helpful if the patient is at the recommended maximum dose but the serum level is not near that of the recommended maximum (thus, the clinician knows the drug dose can be increased, as there is room to achieve a higher AED level)

  • Medication noncompliance: Approximately 30% of patients miss at least 1 dose of their medication every month

  • Autoinduction or pharmacokinetic change, or patients who are unusual metabolizers of a medication

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