Primary Objective:

- To demonstrate the efficacy of at least one dose of SAR110894 (H3 receptor antagonist) in comparison to placebo on cognitive performance in patients with mild to moderate Alzheimer's disease (AD) while on stable donepezil therapy

Secondary Objectives:

• To explore the effect of SAR110894 on functional impairment, global clinical status and behavioral disturbances;
• To assess the safety/tolerability of SAR110894;
• To assess pharmacokinetic (PK) of SAR110894 and concentrations of donepezil;
• To explore caregiver time consumption and distress changes.

The total study duration for each patient is approximatively 36 - 38 weeks broken down as follows:

• Screening period: up to 4 weeks,
• Treatment period: 24 weeks,
• Follow-up period: 10 weeks.

Inclusion criteria:

• Patients with diagnosis of Alzheimer's Disease (AD) (Cannot be dementia from strokes or other causes).
• Patient is on stable and well-tolerated donepezil treatment at a dose of either 5 or 10 mg daily for at least 3 months prior to screening visit.

Exclusion criteria:

• Age <55 years old.
• Psychotic features, agitation, or behavioral problems within the last 3 months.
• Patients unable to comply with ophthalmologic monitoring.
• Lack of consistent and reliable caregiver.

The above information is not intended to contain all considerations relevant to a patient's potential participation in a clinical trial.