This was a phase 1, first-in-human, single-center, randomized, double-blind (participants and investigator blind, sponsor open) placebo-controlled, single-ascending dose study of ACH-0145228 (ALXN2050) conducted in healthy adult participants.

Key Inclusion Criteria:

• Healthy was defined as having no clinically relevant abnormalities identified by a detailed medical history, physical examination, blood pressure and heart rate measurements, 12-lead ECG, and clinical laboratory tests.
• Had a body mass index of 18 to 30 kilograms (kg)/meter squared with a minimum body weight of 50 kg.
• Female participant of nonchildbearing potential.
• Male participant agreed to abstinence or use of a highly effective form of contraception.

Key Exclusion Criteria:

• Had a history or clinically relevant evidence of significant cardiovascular, pulmonary, hepatic, renal, hematological, gastrointestinal, endocrine, immunologic, dermatologic, neurological, or psychiatric disease.
• Had any condition possibly affecting drug absorption.
• Had a body temperature greater than or equal to 38°Celsius on Day -1 or Day 1, Hour 0; had a history of febrile illness, or other evidence of infection, within 14 days prior to first study drug administration.
• Had a positive urine drug screen at Screening or Day -1; was a current tobacco/nicotine user or smoker; had consumed any alcohol within 72 hours before first study drug administration or had a history of regular alcohol consumption within 6 months of Screening.
• Had participated in a clinical study within 30 days prior to first study drug administration
• Had clinically significant laboratory abnormalities,
• Had donated blood or lost more than 500 milliliters of blood within 3 months prior to first study drug administration; had received a blood transfusion or blood products within 6 months prior to first study drug administration.
• Had a clinically significant history of drug allergy.