Donepezil and Memantine in Moderate to Severe Alzheimer's Disease

Participants will be patients who meet NINCDS-ADRDA criteria for probable or possible Alzheimer's disease (McKhann et al, 1984). In addition they will meet all of the following criteria:

1. SMMSE = 5 to 13 (13 chosen as NICE threshold of 10 plus 1 SD on SMMSE score)

2. Continuously prescribed donepezil for at least 3 months

3. Maintained on 10mg donepezil in previous 6 weeks.

4. No changes in prescription of any psychotropic (antipsychotic, antidepressant, benzodiazepine) medication in previous 6 weeks.

5. Prescribing clinician considers (based on NICE guidance, discussions with patient and carer and clinical judgement) that change of drug treatment (i.e. stop donepezil or introduce memantine) may be appropriate.

6. Patient is community resident and has family or professional carer or is visited on at least a daily basis by carer.

7. Patient agrees to participate if considered capable (see section 7.5)

8. Main carer (informal or professional) consents to their own involvement and the patient's involvement -

To maximise the generalisability of the study data, exclusions will be kept to a minimum. These will include:

1. Patient has severe, unstable or poorly controlled medical conditions apparent from physical examination or clinical history.

2. Patient is already prescribed memantine.

3. Patient is unable to take trial medications because of contra-indications or previous adverse or allergic reactions.

4. Patient is involved in another clinical trial.

5. Clinician considers patient would not be compliant with trial medication. -