An Open-label Study to Evaluate the Pharmacokinetics and Safety of Bimekizumab in Pediatric Study Participants With Active Juvenile Idiopathic Arthritis Subtypes Enthesitis-related Arthritis (Including Juvenile-onset Ankylosing Spondylitis) and Juvenile Psoriatic Arthritis

This study is looking for children and young people between 2 and 18 years old who have been diagnosed with enthesitis-related arthritis (including juvenile-onset ankylosing spondylitis) or juvenile psoriatic arthritis for at least three months. Importantly, their arthritis needs to be 'active,' meaning they currently have at least three joints affected and, for enthesitis-related arthritis, at least one area where tendons or ligaments attach to bone is inflamed.

Participants should also have tried at least one anti-inflammatory painkiller (NSAID) for at least a month without enough improvement, or have found it too difficult to take. It's okay if they are already taking certain other medications like methotrexate or sulfasalazine, as long as the dose has been stable for a while. However, they can't be taking most other types of strong arthritis medications.

There are also requirements about body weight (at least 10kg), and for girls, it's important that they are not pregnant or breastfeeding. If they are old enough to potentially become pregnant, they would need to agree to use effective contraception during the study and for several months afterwards.

If you decide to take part, your child would receive regular injections of Bimekizumab under the skin. The study team would closely monitor your child through various clinic visits, which would likely include physical examinations, blood tests, and potentially other assessments to check their arthritis activity and overall health. You would need to attend these visits regularly during the treatment period.

The initial treatment period would be followed by an 'Open-label Extension' where treatment continues, and then a 'Safety Follow-up' period to check on your child's health after the last dose of the medicine. The total length of time your child would be involved in the study, including follow-up after the last dose, could be quite long – potentially over a year or more. You would be fully informed about the schedule of visits and what each visit involves before making a decision.