Pharmacokinetic Study of Oral ALXN1840 in Japanese and Non-Japanese Adult Healthy Participants

The main purpose of the study is to confirm how long ALXN1840 stays in the body of Japanese and non-Japanese healthy participants (that is, pharmacokinetic [PK] profile).

Key Inclusion Criteria: - Body weight ≤80 kilograms (kg) and body mass index (BMI) within the range 18-25 kg/m^2, inclusive, at screening. - Negative serum pregnancy test. - Female participants of childbearing potential and male participants with a female spouse or partner of childbearing potential must be willing to follow protocol-specified contraception guidance starting at least one menstrual cycle before first study drug administration and continuing for up to 3 months after the end of systemic exposure of the study drug (that is, 3 months after end of study visit). Key Exclusion Criteria: - Current or recurrent/chronic disease (for example, cardiovascular, hematological, neurological, endocrine, immunological, rheumatological, renal, hepatic, or gastrointestinal (GI) or other conditions) that or could affect clinical assessments or clinical laboratory evaluations. - Current or relevant history of physical or psychiatric illness that are not stable or may require a change in treatment, use of prohibited therapies during the study or make the participant unlikely to fully comply with the requirements of the study or complete the study, or any condition that presents undue risk from the study drug or study procedures. - Any other significant disease or disorder which, in the opinion of the Investigator, may put the participant at risk. - History of significant allergic reaction (for example, anaphylaxis or angioedema) to any product (for example, food, pharmaceutical). - Use of prescription medications (excluding oral contraceptives) within 14 days prior to dosing on Day 1, except with prior approval of Alexion. - Use of non-prescription/ over-the-counter medications including vitamins and dietary or herbal supplements, within 7 days prior to dosing on Day 1. - Donated or lost 400 milliliters (mL) blood or more within the last 16 weeks preceding the first day of dosing.