This clinical trial is focused on studying a condition known as hereditary angioedema (HAE), which is a rare genetic disorder that causes sudden swelling in various parts of the body, such as the face, hands, and feet. The swelling is due to a deficiency in a protein called C1-Inhibitor. The study is testing a new treatment called PHA-022121, which is taken as a soft capsule by mouth. This medication is designed to prevent the swelling attacks associated with HAE by blocking a specific receptor in the body known as the bradykinin B2 receptor.

The purpose of the study is to evaluate the safety and effectiveness of PHA-022121 in preventing HAE attacks. Participants in the study will be randomly assigned to receive either the new medication or a placebo, which looks like the medication but does not contain the active ingredient. The study is conducted in two parts. In the first part, different doses of the medication will be tested to find the most effective dose. In the second part, the long-term safety of the medication will be assessed. Participants will take the medication over a period of time and will be monitored for any changes in the frequency and severity of their HAE attacks.

Throughout the study, participants will have regular check-ups to ensure their safety and to track the effectiveness of the treatment. The study aims to provide valuable information on whether PHA-022121 can be a safe and effective option for people with hereditary angioedema, potentially offering a new way to manage this challenging condition.