To report a case of Posterior Reversible Encephalopathy Syndrome (PRES) secondary to a common antibiotic treatment combination.

PRES is a life-threatening condition that can cause headache, altered mental status, seizures, and neurologic deficits. Outcome is dependent on rapid recognition and removal of the possible inciting cause. Many medications are known to trigger PRES; however, there is scant literature reporting PRES in the setting of combined ciprofloxacin and metronidazole treatment.

Case report.

A 25-year-old was admitted for hypoxic respiratory arrest after opioid overdose and was found to have pseudomonas bacteremia and tricuspid valve endocarditis. A non-contrast CT (Computed Tomography) head and CT angiogram were negative for any acute findings. She was started on ciprofloxacin and metronidazole for antimicrobial coverage. About 2 weeks after initiation of treatment, the patient was noted to have depressed mental status and right gaze deviation. EEG (electroencephalogram) confirmed seizure activity and a brain MRI (Magnetic Resonance Imaging) showed T2 Fluid-attenuated inversion recovery (FLAIR) hyperintensity of the white matter in the bilateral occipital lobes with patchy diffusion restriction and enhancement. Lumbar puncture revealed isolated elevated protein without pleocytosis. PRES was favored as the etiology given the location of the T2 FLAIR hyperintensities and the sudden occurrence of seizures without any additional inciting cause. Ciprofloxacin and metronidazole were discontinued as potential causes of PRES. Following discontinuation, her mental status gradually improved over the course of days. Repeat MRI one week later showed significant improvement in the FLAIR hyperintensities. 

PRES has a variable clinical presentation making it difficult to determine inciting causes. In this case, there was a clear temporal relationship between antibiotic administration and change in mental status. Whether PRES was caused by metronidazole alone or by the combination with ciprofloxacin remains unclear. Further investigation regarding the association between PRES and the combined antimicrobial treatment are needed.