Start a low-dose antipsychotic for behavioral disturbance, since evening agitation in moderate dementia reflects disease progression requiring pharmacologic management.

Antipsychotics for dementia-related agitation carry a black box warning for increased mortality in elderly patients with dementia. They should be used only after behavioral interventions fail and treatable causes are excluded.

Obtain a CT scan to evaluate for a new cerebrovascular event, since acute behavioral changes in a dementia patient may indicate stroke or subdural hematoma.

A new stroke is possible but the consistent evening-only pattern suggests a behavioral or environmental trigger rather than an acute neurological event, which would typically cause persistent or sudden-onset changes.

Increase memantine dosage to address the behavioral changes, as worsening agitation suggests cognitive decline requiring optimization of the current dementia pharmacotherapy.

Memantine dose adjustment does not address acute behavioral triggers. The evening-only pattern points to situational or environmental factors, not inadequate cognitive medication dosing.

Assess for treatable causes of the evening agitation — including pain, environmental triggers, and unmet needs — before considering any pharmacotherapy.

Behavioral disturbance in dementia is a communication of unmet needs until proven otherwise. Pain is the most commonly overlooked cause — a patient with dementia may not be able to verbalize that her hip hurts when she is repositioned. Evening-specific agitation ("sundowning") has identifiable triggers. Evaluate for pain (arthritis, skin breakdown, constipation), environmental factors (lighting, noise, staffing changes at shift change), unmet needs (hunger, toileting, dehydration), and whether the approach to care is distressing (rushed, unfamiliar staff, lack of verbal cueing). Assess for infection (UTI, pneumonia) when clinically supported by systemic symptoms. Behavioral and environmental interventions are first-line per standard geriatric dementia care guidelines.