Ritlecitinib (PF-06651600) in Participants With Chronic Spontaneous Urticaria

The purpose of this research study is to see if a drug called ritlecitinib is safe and effective for treating chronic spontaneous urticaria (CSU). CSU is hives and itching lasting over six weeks. Ritlecitinib is approved by the Food and Drug Administration (FDA) to treat another condition, but it is not approved for treating CSU. Participation is expected to last 20 weeks and include 7 clinic visits. This study will involve physical examinations, blood tests, looking at and taking pictures of participant's skin and hives, optional skin biopsies, and hearing tests. Eligible participants for this study will take ritlecitinib for 12 weeks and complete a daily diary about their skin and hives. The main risks of being in this study are side effects from ritlecitinib. Less than 1 in 10 people taking ritlecitinib experience diarrhea, acne, hives, rash, inflammation of hair follicles, dizziness, and increased blood levels of creatine phosphokinase (a muscle protein). Participants could also experience a rare but serious side effect, such as shingles, unusual infection, cancer, or blood clot. Benefits of participating in this study include a potential improvement in participant's condition and quality of life. Participating in this study may also help researchers develop new ways of helping future patients.