A Phase II, Cross-over Clinical Trial Evaluating the Efficacy and Safety of KVD900 (Sebetralstat) in the On-demand Treatment of Angioedema Attacks in Adult Subjects With Hereditary Angioedema Type I or II

Inclusion Criteria: * Male or female adult subjects 18 years of age and older. * Confirmed diagnosis of HAE type I or II at anytime in the medical history * At least 3 documented HAE attacks in the past 93 days, as supported by medical history. * Access to and ability to use conventional attack treatment for attacks of HAE * Adequate organ functions * Females of childbearing potential must agree to use highly effective birth control from the Screening visit until the end of the trial follow-up procedures. * Females of non-childbearing potential, defined as surgically sterile (status post hysterectomy, bilateral oophorectomy, or bilateral tubal ligation) or post-menopausal for at least 12 months, do not require contraception during the study * Males with female partners of childbearing potential must agree to be abstinent or else use a highly effective method of birth control as defined in inclusion 6 from the Screening visit until the end of the trial follow-up procedures * Provide signed informed consent and are willing and capable of complying with study requirements and procedures Exclusion Criteria: * Any concomitant diagnosis of another form of chronic angioedema, such as acquired C1 inhibitor (C1-INH) deficiency, HAE with normal C1-INH (also known as HAE type III), idiopathic angioedema, or angioedema associated with urticaria * Current use of C1INH, androgens, or tranexamic acid for HAE prophylaxis * Use of angiotensin-converting enzyme (ACE) inhibitors or any estrogen-containing medications with systemic absorption (such as oral contraceptives or hormonal replacement therapy) within 93 days prior to initial study treatment. * Use of androgens (e.g. stanozolol, danazol, oxandrolone, methyltestosterone, testosterone) or antifibrinolytics within 30 days prior to initial study treatment. * Use of lanadelumab within 10 weeks prior to initial study treatment. * Use of strong CYP3A4/CYP2C9 inhibitors and inducers during participation in the trial * Clinically significant abnormal ECG at Visit 1 and pre-dose at Visit 2. This includes, but is not limited to, a QT interval by Fredericia, QTcF \> 470 msec (for women) or \> 450 msec (for men), a PR \> 220 msec or ventricular and/or atrial premature contractions that are more frequent than occasional and/or occur as couplets or higher in grouping * Any clinically significant history of angina, myocardial infarction, syncope, clinically significant cardiac arrhythmias, left ventricular hypertrophy, cardiomyopathy, or any other cardiovascular abnormality * Any other systemic dysfunction (e.g., gastrointestinal, renal, respiratory, cardiovascular) or significant disease or disorder which, in the opinion of the Investigator, would jeopardize the safety of the subject by taking part in the trial * History of substance abuse or dependence that would interfere with the completion of the study, as determined by the Investigator * Known lactose allergy or intolerance * Known hypersensitivity to KVD900 or placebo or to any of the excipients * Participation in an interventional investigational clinical study within 93 days or within 5 half-lives of the last dosing of investigational drug (whichever is longer) prior to initial study treatment * Any pregnant or breast-feeding subject