Q. A 60 year-old female presents with encephalopathy. Her son notes that the patient has difficulties with orientation, grooming, and driving that started 2 weeks ago. She has also fallen several times during the last 2 weeks. Her past medical history includes chronic alcohol use involving at least 5-10 alcoholic drinks daily for the last 35 years. Vital signs are normal. On neurological examination, she is noted to confabulate answers. Her neurological exam reveals gaze evoked binocular horizontal nystagmus and a wide-based gait. Her MRI brain with and without contrast strongly suggests Wernicke's encephalopathy. Which of the following supplements should be given to this patient to prevent worsening of her neurological symptoms?