Here is the design of a clinical trial:

Official Title: Efficiency of Donepezil in Elderly Patients Undergoing Orthopedic Surgery Due to Underlying Postoperative Cognitive Dysfunction, a Multicenter Randomized Controlled Trial

Included conditions:
- Total Knee Arthroplasty
- Fracture of Head of Femur Articular Displaced
- Protrusion of Intervertebral Disc

Study Armgroups:
- {'label': 'Control', 'type': 'PLACEBO_COMPARATOR', 'interventionNames': ['Drug: Placebo']}
- {'label': 'Donepezil', 'type': 'EXPERIMENTAL', 'interventionNames': ['Drug: Donepezil']}

Interventions:
- {'type': 'DRUG', 'name': 'Donepezil', 'description': 'Donepezil a cholinesterase inhibitor, 5mg(1 pill)/ day for 7 days Po, was administrated from the day before surgery.', 'armGroupLabels': ['Donepezil']}
- {'type': 'DRUG', 'name': 'Placebo', 'description': 'Placebo, 1 pill/ day for 7 days Po, was administrated from the day before surgery.', 'armGroupLabels': ['Control']}

Primary Outcomes:
- {'measure': 'The incidence of POCD after the surgery.', 'timeFrame': 'up to 7 days'}

Please estimate the sample size based on the assumption: 
Power of 0.80, two-sided significance level of 5%, and a dropout rate of 10%.
Sample size
        In the previous study, we found that the POCD incidence in the elderly patients undergoing orthopaedic surgery is about 25% [20]. The anticipated effect size of donepezil is 50%. That means the power analysis for the primary outcome of POCD prevalence assumes a reduction from 25 to 12.5%. The results of a conventional analysis to detect differences in proportions (POCD) between the intervention and control groups, using PASS19.0, led to a total of 300 patients with a 1:1 randomisation, given a power of 1 â Î² = 0.80 and a two-side Î± level of 5%. Assuming a dropout rate of 10%, this results in a requirement of about 360 total patients.