Individual-level data were extracted from medical charts by neurologists/epileptologists at various clinical practices in the US. Eligible adult subjects had confirmed FOS and initiated 3rd line ASM therapy (LT) (indicating DR per ILAE definition, initiation date = index date), and had medical history available for ≥1 year before (baseline) and ≥2 years after index date (follow-up period). No minimum follow-up was required for subjects initiating cenobamate.

Study included 345 subjects. Mean (SD) age was 32.4 (11.2) years, 65.5% male, 78.3% White/Caucasian, and 64.6% covered by commercial/private insurance. The most prevalent baseline neuropsychiatric comorbidities were anxiety (31.6%), depression (29.3%) and migraine (13.3%). The frequent baseline ASM regimens were all monotherapies:  levetiracetam (25.2%), carbamazepine (13.3%) and phenytoin/fosphenytoin (12.5%) in 1^st LT; levetiracetam (11.3%), lamotrigine (8.4%) and carbamazepine (5.8%) in 2^nd LT. All subjects had ≥1 seizure/month during the last 6 months of baseline: mean (SD) rate 6.1 (7.7) seizures/month. At follow-up, the mean (SD) was 3.8 (7.2) seizures/month. Compared to baseline, 27%, 22%, 18%, 5% and 28% subjects at follow-up experienced no (≤0%), some (1%-49%), moderate (50%-74%), significant (75-89%) and greatest (≥90%) seizure frequency reduction, respectively. At follow-up, 70% of hospitalizations were unplanned. Breakthrough seizures were the most common reason for hospitalization.  

People with DR-FOS have significant comorbidities. Most do not have sufficient seizure control after initiating 3^rd LT treatment and utilize significant healthcare resources.