Drug-induced seizures and delirium are common among patients with critical illnesses, especially those in an intensive care unit. With an increase in the use of potent, broad-spectrum antibiotics, the etiology for encephalopathy remains under-recognized. Antibiotics-induced nonconvulsive seizures should also be considered in patients with unexplained mental status, therefore continuous electroencephalography monitoring is often needed for its detection. Prompt discontinuation, substitution, or dose adjustment of the causative antibiotics might help improve prognosis. Also, antibiotics should be used with caution especially in patients with known epilepsy, central nervous system disorders, critical illnesses, or renal dysfunction.