How Often Do Antibiotics Cause Delirium?

Type 2 AAE is marked by onset within days of antibiotic initiation, frequent occurrence of psychosis, rare occurrence of seizures, infrequently abnormal EEG, normal MRI, and resolution within days. This clinical phenotype is associated with procaine penicillin, sulfonamides, fluoroquinolones, and macrolides.

Type 3 AAE is seen only with metronidazole and is characterized by onset weeks after initiation, frequent occurrence of cerebellar dysfunction, rare seizures, rare and nonspecific EEG abnormalities, and omnipresence of abnormal MRI.

Reports’ Level of Detail Varied

Any review that relies exclusively on case reports and small series is subject to selection and publication bias, which may explain why the median age for AAE in reported cases was relatively young, said the authors. Also, AAE in the elderly may be underreported because delirium in this population may result from several factors.

The case reports that Dr. Bhattacharyya’s group collected had varying degrees of detail, and missing information prevented a precise estimation of the prevalence of reported symptoms and laboratory findings. The authors tried to reduce the effect of such variability on their analysis by reviewing a large number of cases. Many case reports, though, did not include enough clinical information to exclude other potential contributing factors to encephalopathy, and this lack of detail affected the strength of the association that the researchers found.

“More research is needed, but these antibiotics should be considered as a possible cause of delirium,” said Dr. Bhattacharyya. “Recognition of different patterns of toxicity could lead to a quicker diagnosis and hopefully prevent of some of the negative consequences for people with delirium and other brain problems.”

—Erik Greb