Delirium is a disorder of consciousness characterized by an acute onset and fluctuating course of impaired cognitive functioning. It is associated with unfavorable outcomes in hospitalized patients, including longer hospital length of stay, need for subsequent institutionalization and higher mortality rates. Patients in the intensive care unit (ICU) under mechanical ventilation and older age are at higher risk for the development of delirium. Several studies suggest that minocycline, through its anti-inflammatory effect, was able to prevent neuronal dysfunction in different models of ICU-related diseases. Thus, the present study aimed to evaluate the effect of minocycline on delirium development in critically ill patients. Patients will be randomized into one of two groups: the intervention group that will receive 100mg of minocycline 2 times a day and the placebo group. Medication or placebo will be continued for 28 days or until ICU discharge (whichever occurs first). Delirium will be diagnosed by the CAM-ICU. Coma will be defined by the Richmond Agitation-Sedation Scale (RASS) score of -4 or -5 and biomarkers will be used as alternative outcomes related to the pathophysiology of the disease (IL-1, IL-6, IL-10, and BDNF).

Inclusion Criteria:

• Clinical or surgical patients,
• Over 18 years,
• Expected ICU stay of at least 2 days estimated by the attending intensivist,
• Agree to participate in the study

Exclusion Criteria:

• Delirium prior to inclusion,
• Diagnosis of Parkinson's disease
• Diagnosis of dementia,
• Alcohol abuse history,
• Acute neurological condition at admission
• History of psychiatric disease
• Use of antipsychotics
• Pregnant or breastfeeding women,
• Expectation of death within 2 days
• Hospitalized for exclusive palliative care
• Known allergy to minocycline

Placebo capsules looking identical to minocycline capsules