Study to Evaluate the Safety and Efficacy of USL261 (Intranasal Midazolam) in Patients With Seizure Clusters

Inclusion Criteria: * Has a competent, adult caregiver who can recognize and observe the subject's seizure cluster episodes * Has an established diagnosis of partial or generalized epilepsy that includes the following: * A documented history of seizure clusters lasting a minimum of 10 minutes * Seizure cluster pattern is observable, stereotyped, and recognizably different from the subject's other non-cluster seizure activity (if any) * A second seizure in the seizure cluster typically occurring within 6 hours from the time of cluster recognition * A seizure cluster pattern composed of multiple (≥ 2) partial or generalized seizures * A seizure cluster pattern established \> 3 months before Visit 1 * A frequency of ≥ 3 seizure clusters during the year before Visit 1 * At least 1 seizure cluster occurring ≤ 4 months before Visit 1 * Seizure cluster pattern is confirmed by a central reviewer * Currently on a stable regimen of anti-epileptic drugs (AEDs) with no changes in type of AEDs since Visit 1 and for ≥ 7 days before Visit 2, with or without intermittent use of benzodiazepines at a constant dose * Weight is 40 kg to 125 kg, inclusive Exclusion Criteria: * Has a neurological disorder that is likely to progress in the next year * Has severe chronic cardio-respiratory disease * Has had psychogenic, non-epileptic seizure(s) within the 5 years before Visit 1 * Has a history of their stereotypical seizure cluster progressing to status epilepticus within the 2 years before Visit 1 * Has a history of acute narrow-angle glaucoma. * Has had active suicidal plan/intent or active suicidal thoughts in the 6 months before Visit 1 or a suicide attempt in the past 5 years * Currently using a vagal nerve stimulator (VNS) unless the device has been implanted for at least 6 months and the setting stable for 4 weeks before Visit 1