We explored the efficacy and safety of lacosamide combined with inhibitors of fast-inactivated sodium channels or with other antiepileptic drugs, in patients with drug refractory focal epilepsy associated with intellectual or psychiatric disability.
Observational study of lacosamide including the monitoring of lacosamide trough plasma levels and of electroencephalograms.
We followed up 44 patients from the start of lacosamide therapy for up to 3 years, with a clinical, electroencephalogram (EEG), and pharmacological follow-up. Median patients’ age was 32.7 years, median age at epilepsy onset was 3.5 years. Intellectual disability was severe in 55.4% of the cohort and drug refractoriness was diagnosed in 88.6% of patients, who had predominantly focal seizures (80%). The severity of their epilepsy was suggested by the use of combined therapies with non-sodium blockers and sodium blockers in 75% of patients. Lacosamide was added to previous therapies and up-titrated to a median of 300 mg/d. Lacosamide add-on led to simplification of the previous drug regimen with a dose reduction in 87.9% of users of sodium blockers and in 66.7% of users of non-sodium blockers, and to withdrawal of previously administered sodium blockers in 48.5% users and non-sodium blockers in 47.6% users. Lacosamide was prescribed at lower doses in the presence of oxcarbazepine (p = 0.029), lamotrigine (p = 0.015), and topiramate (p < 0.001). Mean lacosamide plasma levels were 6.0 ± 2.4 mg/L; they were in linear correlation with the administered dose (R = 0.38, p < 0.001) and were influenced by the association with lamotrigine (p = 0.008), zonisamide (p = 0.012), and clobazam (p = 0.028). Lacosamide combination regimens led to an average reduction of 42% in baseline seizure frequency, with 50% patients reporting ≥50% seizure frequency reduction. Efficacy was directly correlated with lacosamide dose (R = 0.47, p < 0.001, B = 0.53) and trough plasma levels (R = 0.31, p < 0.001, B = 0.16). Electroencephalogram profiles were improved in 40.9% of patients and EEG improvement was not significantly correlated with seizure frequency reduction. Lacosamide safety was good, with 37 adverse reactions in 30 patients, of which 50% were attributed to lacosamide and led to lacosamide withdrawal in 18% of cases. The retention rate of lacosamide was of 88.6% at 1 year, 86.4% at 2 years, and 72.7% after three years. The severity of intellectual disability was directly correlated with increased possibility of lacosamide retention (OR = 0.46 per severity tier, p = 0.016).
Lacosamide add-on allowed dose reduction of previous therapies and reduced the frequency of seizures, showing good tolerability even at high doses, without exceeding reference plasma levels.

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