The study was terminated due to enrolment challenges

The main purpose of this study is to investigate effects of Lu AG06466 on seizure activity after increasing daily doses during 4 weeks in participants with an implanted responsive neurostimulation system.

This crossover study consists of 2 treatment periods, each of 29 days duration. On Day -1 of treatment period 1, eligible participants will be randomized (1:1) to a sequence of treatments (either Lu AG06466-placebo or placebo-Lu AG06466).

Key Inclusion Criteria:

• The participant must have had the responsive neurostimulation system (RNS®) System implanted for more than 1 year and medically intractable focal onset epileptic seizures (history of persistent seizures refractory to 2 or more anti-epileptic drugs [AEDs]), with seizures from all foci represented in the implanted RNS electrodes.
• The participant is required to have a continuous period of at least 2 months prior to the Screening Visit with constant RNS stimulation settings as well as stable AED (that is, 60 days with no dose adjustments of more than 25%) as determined by medical history and the Patient Data Management System (PDMS). There must be at least 24 recorded long episodes available for review since last change of RNS detection setting.
• The participant is required to have approximately 7 or more long episodes per week, as assessed as an average over the last 2 months prior to the Screening Visit.
• The participant is required to have a demonstrated history of compliance with RNS scanning and uploading procedure in the past year (less than 20% missing long episode counts on the PDMS).

Key Exclusion Criteria:

• The participant has the RNS System implanted in other regions than the epileptic foci such as the thalamus.
• The participant has a RNS System with anticipated generator change in the coming 6 months.
• The participant has a cyclic pattern of long episodes in the last 2 months prior to the Screening Visit which exhibits, in the opinion of the investigator: a period of more than 3 weeks; and peak-to-trough differences of long episodes of more than half the peak level.
• The participant has or has had any clinically significant immunological, cardiovascular, respiratory, metabolic, renal, hepatic, gastrointestinal, endocrinological, haematological, dermatological, venereal, neurological (apart from epileptic diagnosis), or psychiatric disease or other major disorder, which in opinion of the investigator may influence efficacy or safety aspects in the study.

Other inclusion and exclusion criteria may apply.