Melatonin for Prevention of Kidney Injury

Inclusion criteria: * Aged 18 to 75 years * Currently prescribed vancomycin with the presumption that therapy will be continued for at least 3 days based on a review of subject status. Because of the critical nature of starting empiric broad-spectrum antibiotics, we will allow one dose of the antibiotic combination before consent and enrollment. This strategy is necessary for the ethical conduct of the study. Exclusion criteria: * Estimated creatinine clearance \< 30 mL/min * Liver impairment (liver enzymes \> 3 times upper limit) * Any history of allergy or contraindication to melatonin * Pregnancy or breastfeeding * Autoimmune disease * Requiring vasopressors * Requiring mechanical ventilation * History of acute kidney injury in the past 30 days * Inability to take oral medications * Clinical evidence of significant unstable or uncontrolled illness which, in the opinion of the research team, could confound the results of the study or put the patient at undue risk.