This will be an open-label, 3-sequence, 3-period crossover study in healthy adult participants to assess the relative bioavailability of ACH-0145228 when administered as an immediate release tablet versus powder-in-capsule.

Inclusion Criteria:

1. Body mass index in the range of 18.0 to 32.0 kilograms (kg)/meter squared, inclusive, with a minimum body weight of 50.0 kg at screening.
2. No clinically significant history or presence of electrocardiogram findings at screening.
3. Non-sterile male participants must agree to abstinence or use a highly effective method of contraception.
4. Female participants must be of non-childbearing potential and need not employ a method of contraception.

Exclusion Criteria:

1. Clinically significant laboratory abnormalities.
2. History of any medical or psychiatric condition or disease that might limit the participant's ability to complete or participate in this clinical study, confound the results of the study, or pose an additional risk to the participant by their participation in the study.
3. History or presence of drug or alcohol abuse within previous 2 years, current tobacco user, and positive drugs-of-abuse screen and alcohol screen at screening or Day -1 of Period 1.
4. History or presence of clinically significant seizures, head injury, or head trauma.
5. History of procedures that could alter absorption or excretion of orally administered drugs.
6. History of meningococcal infection, or a first-degree relative with a history of meningococcal infection.
7. A history of significant multiple and/or severe allergies or has had an anaphylactic reaction or significant intolerability to prescription or non-prescription drugs.
8. Body temperature ≥ 38.0°Celsius at screening or prior to first dosing in Period 1 or history of febrile illness, or other evidence of infection, within 14 days prior to (first) dosing.
9. Is a female of childbearing potential.
10. Donation of whole blood from 3 months prior to first dosing, or of plasma from 30 days before first dosing, and receipt of blood products within 6 months prior to first dosing.
11. Participation in any other investigational study drug trial in which receipt of an investigational study drug occurred within 5 half-lives (if known) or 30 days before first dosing, whichever is longer.