Single antiepileptic drug levels do not predict adherence and nonadherence

Area of Science:

• Neurology
• Clinical Pharmacology
• Epilepsy Management

Background:

• Assessing patient adherence to antiepileptic drugs (AEDs) is critical for effective epilepsy management.
• Interpreting AED plasma levels requires understanding factors beyond patient adherence.

Purpose of the Study:

• To determine the relationship between "subtherapeutic" vs "therapeutic" antiepileptic drug (AED) plasma levels and patient treatment adherence.
• To investigate the causes of subtherapeutic AED plasma levels in patients with refractory epilepsy.

Main Methods:

• Video-electroencephalography (EEG) monitoring was performed on 170 patients with refractory temporal lobe epilepsy.
• Antiepileptic drugs (AEDs) were rapidly withdrawn, and plasma levels were measured over three days.
• Adherence was identified by plasma level changes, and frequencies of initial low levels were compared between adherent and nonadherent groups.

Main Results:

• Adherence was observed in 73.2% of patients, with nonadherence in 26.8%.
• Low AED plasma levels occurred equally in both adherent and nonadherent groups (approximately 25% of cases).
• Most low levels (73.7%) were attributed to factors other than nonadherence, such as low-dose treatment or enzyme induction.

Conclusions:

• "Subtherapeutic" AED plasma levels are infrequently caused by nonadherence.
• "Therapeutic range" levels do not guarantee patient adherence.
• Individualized monitoring of AED plasma levels, comparing multiple measurements for the same patient, is essential for accurate interpretation.