Extension Study of Oral PHA-022121 for Acute Treatment of Angioedema Attacks in Patients With Hereditary Angioedema

Key Inclusion Criteria:

1. Provision of written informed consent. If the participant is a minor (i.e., <18years of age or as determined by local law), consent will be obtained from theparticipant's parent/legally designated representative/guardian and written assentwill be obtained from the participant, per country regulations.

2. For participants from Study C201, received at least one dose of study drug (including the non-attack visit) in Study C201. For participants from Study C306,participant was randomized (and for adolescent participants 12 to <18 years receiveda dose of study drug in a non-attack state at Visit 1) and completed Study C306,with 2 attacks treated, or after closure of that study by the Sponsor. Enrollment of adolescents (≥12 to <18 years or age of adulthood as defined locally)from these studies is with consideration of local age requirements.

3. Female participants of childbearing potential (or who become of childbearingpotential during the study) must agree to the protocol-specified pregnancy testingand to be abstinent from heterosexual intercourse or to use an acceptablecontraception method as defined in the protocol and as available locally fromenrollment until 30 days after the last study drug administration.

4. In the opinion of the Investigator, the participant (and parent/caregiver foradolescent participants) is willing and able to comply with the protocol.

Key Exclusion Criteria:

1. Any female who is pregnant, plans to become pregnant, or is breast-feeding.

2. Any other systemic disease (e.g., cardiovascular, gastrointestinal, renal,respiratory, neurological) or significant disease or disorder that, in the opinionof the Investigator, would interfere with the participant's safety or ability toparticipate in the study.

3. Use of lanadelumab for long-term HAE prophylactic therapy within 12 weeks prior toenrollment in Part A.

4. For Part A: Use of C1-esterase inhibitor, oral kallikrein inhibitors, attenuatedandrogens, anti-fibrinolytics, or monoclonal HAE therapy within a defined periodprior to enrolment. For Part B: If a participant is receiving long-term prophylactic therapy with one ofthe following medications indicated for HAE: plasma-derived C1-INH, danazol at lessthan or equal to 200 mg/day, anti-fibrinolytics, berotralstat, or lanadelumab, theymust be on a stable dose and regimen for at least 3 months before screening andintends to remain on the same dose for the duration of the study.

5. History of alcohol or drug abuse within defined period, or current evidence ofsubstance dependence or abuse

6. Participation in any other investigational drug study within defined period

7. Discontinued from parent study after enrollment for any study drug-related safetyreason or non-compliance including significant protocol deviation.

8. Use of concomitant medications that are strong CYP3A4 inhibitors (e.g.,clarithromycin, erythromycin, itraconazole, ketoconazole, ritonavir) or strongCYP3A4 inducers (e.g., carbamazepine and phenytoin).