Study terminated due to slow enrollment. There were no safety concerns.

The purpose of this study is to examine the long-term safety and tolerability of USL261 in the treatment of seizure clusters.

Inclusion Criteria:

1. Has a competent, adult caregiver(s) who is able to recognize and observe the subject's seizure cluster episodes

2. Has an established diagnosis of partial or generalized epilepsy that includes all 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 occurs within 6 hours from the time of 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 stereotyped seizure clusters during the year before Visit 1
   • At least 1 stereotyped seizure cluster occuring ≤ 4 months before Visit 1

3. Currently on a stable regimen of AED(s) that includes a benzodiazepine

4. Weight is 40 kg to 125 kg, inclusive

Exclusion Criteria:

1. Has a neurological disorder that is likely to progress in the next year
2. Has a severe chronic cardio-respiratory disease
3. Has a psychogenic, non-epileptic seizure(s) within the 5 years before Visit 1
4. Has a history of their stereotypical seizure cluster progressing to status epilepticus within 2 years before Visit 1
5. Has a history of acute narrow-angle glaucoma
6. 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

A manuscript or abstract should not be submitted by investigator(s) for publication or presentation until a New Drug Application is approved by the US FDA or permission is granted in writing by the sponsor.