Here is the design of a clinical trial:

Official Title: The VITDALIZE Study: Effect of High-dose Vitamin D3 on 28-day Mortality in Adult Critically Ill Patients With Severe Vitamin D Deficiency: a Multicenter, Placebo-controlled Double-blind Phase III Randomized Controlled Trial (RCT)

Included conditions:
- Critical Illness
- Vitamin D Deficiency
- Covid19

Study Armgroups:
- {'label': 'Placebo', 'type': 'PLACEBO_COMPARATOR', 'description': 'oral/enteral loading dose of 37.5 ml MCT followed by 10 drops daily for 90 days', 'interventionNames': ['Drug: Placebo']}
- {'label': 'High Dose Vitamin D3', 'type': 'EXPERIMENTAL', 'description': 'oral/enteral pharmacological dose of cholecalciferol (vitamin D3) - total dose 900,000\n\n* loading dose of 540,0000 (dissolved in 37.5 ml of medium chain triglycerides - MCT)\n* followed by 4000 IU daily (10 drops) for the entire active study period (90 days)', 'interventionNames': ['Drug: Cholecalciferol']}

Interventions:
- {'type': 'DRUG', 'name': 'Cholecalciferol', 'description': 'oral/enteral loading dose of 37.5 ml MCT including 540,000 IU vitamin D3 followed by 10 drops daily (4000 IU) for 90 days', 'armGroupLabels': ['High Dose Vitamin D3'], 'otherNames': ['Vitamin D3']}
- {'type': 'DRUG', 'name': 'Placebo', 'description': 'oral/enteral loading dose of 37.5 ml MCT followed by 10 drops daily for 90 days', 'armGroupLabels': ['Placebo']}

Primary Outcomes:
- {'measure': '28-day mortality', 'description': 'all-cause mortality', 'timeFrame': '28 days'}

Please estimate the sample size based on the assumption: 
The study uses a two-sided log-rank test with a significance level of 5% and a power of 80%. It also accounts for a 10% dropout rate and includes one interim analysis using an O'Brien-Fleming spending function.
Sample size considerations
        The sample size for this multinational study is based on the primary endpoint 28-day mortality. In the VITdAL-ICU study, 28-day mortality rates of 36% (37/102) in the placebo group and 20% (20/98) in the vitamin D Group were observed.6 The VITDALIZE study has been designed to be sufficiently powered to detect a smaller, but clinically relevant absolute mortality difference of 5% with a power of 80% with an assumed baseline mortality rate of 25%. This corresponds to a clinically highly relevant relative risk reduction of 20%.
        Multicentre trials generally have a smaller treatment effect than monocentre studies.9 We assume that this will also be the case for the VITDALIZE study. Furthermore, our assumed 5% absolute mortality difference is in line with a recent survey among clinical intensivists that the largest median treatment effect considered plausible by intensivists for current ongoing ICU multicentre trials is 3%â5%.10

        Using a fixed sample size design and a two-sided log-rank test for equality of survival curves with a two-sided alpha level of 5%, a sample size of n=1093 per group will be needed to achieve a power of 80% (total sample size of 2186).
        Incorporating one interim analysis after inclusion of 50% of the patients a total sample size of at least n=2194 (494 events) is required to achieve 80% power using an OâBrien-Fleming spending function.11 Accounting for a drop-out rate of approximately 10% yields a total sample size of n=2400 patients. For sample size calculation the software package nQuery 7.0+nTerim 2.0 was used.