This study is designed to evaluate the efficacy, safety, and tolerability of USL261 compared with that of intranasal (IN) placebo for the treatment of intermittent bouts of increased seizure activity.

Inclusion Criteria:

• Subject has been admitted to the institution's EMU for seizure characterization or pre-surgical evaluation, or such admission is planned within 28 days
• Subject body weight is ≥ 40 kg to ≤ 125 kg (inclusive)
• Subject has an established diagnosis of partial or generalized epilepsy

Exclusion Criteria:

• Subject has history of status epilepticus in the 6 months prior to Screening
• Subject has a progressive neurological disorder such as brain tumor, demyelinating disease, or degenerative central nervous system (CNS) disease that is likely to progress in the next 12 months
• Subject has respiratory failure (or is at risk for respiratory failure) or other severe cardiorespiratory disease with New York Heart Association Class III or IV functional status, or requires supplemental oxygen
• Subject has acute narrow-angle glaucoma
• Subject is receiving chronic benzodiazepine treatment (defined as an average of ≥ 4 administrations per week) and cannot safely withdraw from such treatment within the washout period prior to treatment