Blood tests are often checked before treatment with an antiepileptic drug (AED) begins. These results can then be compared with blood tests that are done after you have been taking the AED for some time, to see if there have been any changes.

What do the blood tests measure?

These tests include measurements of electrolyte levels (chemicals in the blood such as sodium and potassium), liver and kidney function tests, blood-cell counts, and monitoring of antiepileptic drug levels.

Once a person begins taking medication, how often does he or she require blood tests?

The frequency of testing varies considerably from doctor to doctor and even country to country. In the United States, blood tests are often done routinely several weeks or months after a new drug is started. The timing of later tests depends on the patient's medical history, the drug and, most importantly, the doctor's opinion on the necessity for testing.

What does the therapeutic range of blood levels refer to?

The so-called therapeutic range of blood levels for antiepileptic drugs is the range of levels at which most patients have good seizure control and few or no adverse effects. The lower and upper limits of this range can vary between different laboratories and doctors.

When is the best time to test blood levels of a drug?

Checking the blood level of a drug at consistent times of day and consistent times after the last dose of medication is taken allows the doctor to compare levels at different dosages. Routine blood levels are best measured when the amount of the drug in the bloodstream is at its lowest point, which is called the trough level. This generally corresponds to the time just before the medication is taken.

Is the blood drug level the main criterion used to determine the effectiveness of treatment?

No. Seizure control without adverse effects, not the blood drug level, is the criterion for judging the efficacy of treatment. For example, if a patient's seizures are well controlled but the level of drug in the blood is below the expected therapeutic range, the doctor will usually be satisfied and will not increase the dosage to raise the blood drug level.

Topic Editor:Steven C. Schachter, M.D.
Last Reviewed:12/15/06