after joining the study you will be assigned by a computer to receive either sar448851 or a matched placebo. the assignment is unknown to you and the study staff.

you will have an initial visit where blood is drawn, a brain scan called a mri is performed, and a special imaging test called a pet scan is scheduled.

you will begin taking one oral capsule each day. the capsule contains 25 mg of sar448851 if you were assigned to the active group, or no active drug if you were assigned to the placebo group.

the capsule is taken by mouth with water, preferably at the same time each day, for the next 48 weeks.

shortly after the first medication dose you will receive an intravenous injection of the tracer mk-6240 (185 MBq). the injection is given into a vein and lasts only a few seconds.

the tracer allows a pet scan to measure amyloid plaques in the brain. you will lie on a scanner table while images are taken; the procedure takes about 30 minutes.

you will return to the clinic at weeks 4, 12, 24, 36 and 48. at each visit you will:

• provide a blood sample for laboratory tests and to measure the level of sar448851 in your body.
• undergo safety checks such as blood pressure, heart rhythm (ecg), and a brief questionnaire about side effects.
• receive a brief physical examination.

if any side effects occur, the study staff will record them as treatment‑emergent adverse events (events that start after you begin the medication).

you will keep taking the assigned capsule every day for the full 48‑week period. missing doses should be avoided; if a dose is missed, you should take it as soon as you remember unless it is close to the next scheduled dose.

at week 48 you will have a final set of assessments similar to the earlier visits, including blood tests, a brain mri, and another pet scan with mk-6240 to compare changes over time.

after week 48 you may choose to continue in an open‑label extension. in this part all participants receive the active drug sar448851 at the same 25 mg daily dose, regardless of earlier assignment.

the open‑label period lasts an additional 48 weeks, up to week 96.

during weeks 60, 72, 84 and 96 you will attend clinic visits that include the same safety checks, blood sampling, and imaging procedures as before.

the purpose is to monitor long‑term safety and to measure changes in disease‑related biomarkers.

at the end of week 96 a final evaluation is performed. this includes a blood draw, a brain mri, and a pet scan with mk-6240 to assess the overall effect of the medication over the 96‑week period.