A 57-year-old alcohol-dependent male presents to the emergency department with acute global confusion, psychosis, and ataxia. Vital signs show BP 128/82 mmHg, HR 102/min, RR 18/min, temperature 37.2°C, and SpO2 98% on room air. Physical examination reveals bilateral ophthalmoplegia and distal polyneuropathy. MRI brain demonstrates mammillary body atrophy. Blood glucose is 98 mg/dL. The patient denies recent thiamine supplementation. Which vitamin should be administered immediately?

1. A)ThiamineGABARITO
2. B)Riboflavin
3. C)Niacin
4. D)Pyridoxine
5. E)Biotin