24 Weeks Double-blind Randomized Placebo-controlled Trial to Evaluate Efficacy, PK, Safety of LOU064 in Adolescents (12 - <18) With CSU and Inadequate Response to H1-antihistamine Followed by Optional 3 Years Open-label Extension and an Optional 3 Years Safety Long-term Treatment-free Follow-up

To join this study, you must be a male or female teenager aged between 12 and 17. You need to have had chronic hives (urticaria) for at least six months, and these hives shouldn't have improved enough even though you've been taking standard allergy pills (H1-antihistamines) as advised by your doctor. You also need to have experienced hives and itching frequently in the weeks leading up to the study, and these symptoms will be measured during the screening process.

There are also reasons why you wouldn't be able to join. For example, if you've already taken this specific experimental medicine or similar ones before. You also can't participate if you have certain health conditions like a significant risk of bleeding, a history of serious stomach bleeding, or specific heart, liver, or kidney problems. If you're allergic to any of the study medicines or similar types, or if your hives have a clear, single trigger (like a specific allergy to something), then you wouldn't be able to take part.

If you join this study, it will be split into three main parts. First, for about 32 weeks, you'll be in the 'core period' where you'll visit the study site about 10 times. During this time, you'll receive either the study medicine (LOU064) or a dummy treatment (placebo) – you won't know which one. This is followed by an optional 'open-label extension' which could last from one year up to three years, with 3 to 15 visits depending on your hives. In this part, if your doctor agrees, you'll receive LOU064. Finally, there's an optional 'long-term follow-up' for three years, with one visit and up to four phone calls, where you won't receive any treatment but will be monitored for your health. The total time you could be involved in the study ranges from about 8 months to over 6 years.