Abstract Background Numerous reports have emerged about the neurotoxic effects of ertapenem. A recent study supports carbapenem use for the treatment of extended spectrum β-lactamase (ESBL)- producing Gram-negative bacteremia. This will likely bolster the use of ertapenem as it is a convenient choice to complete antibiotic treatment in an outpatient setting. This study aims to review the incidence of neurotoxicity with ertapenem and the risk factors associated with it. Methods A retrospective nested cohort study was conducted in Changi General Hospital in Singapore from January 2015 to Decemeber 2016. All patients who received at least 24 hours of ertapenem were identified. Those who exhibited ertapenem-associated neurotoxic effects were selected as cases while those who did not were included in the pool of controls and randomly selected at a 1:3 ratio. Results A total of 544 patients were treated with ertapenem in our hospital during this 2-year period. Twenty-five patients (incidence 4.6%) developed neurotoxic manifestations and 75 patients were included as controls. Acute confusion was the commonest reaction (n = 19, 76%) followed by hallucinations (n = 8, 32%) and seizures (n = 5, 20%). Baseline characteristics were similar in both groups; the median age of the cases was 79 years (IQR 71–83 years) and 14 (56%) were males. The median duration of ertapenem use before neurotoxicity occurred was 7 days (IQR 5–11days). The median Naranjo ADR probability score for cases was 7 (range 5 to 7) which suggests a probable relationship. Univariate analysis showed that renal impairment (with CrCl< 60 mL/minute) (OR 3.31, 95% CI 1.03–10.64), a history of a vulnerable brain (including stroke and epilepsy etc)(OR 2.61 95% CI 1.03–6.61) increased the risk of neurotoxicity. Neurotoxicity was also significantly associated with longer hospitalization (median 21 days, p = 0.03). Conclusion Our study suggests that renal impairment or a history of vulnerable brain may increase the risk for ertapenem-associated neurotoxicity. Hence, caution should be exercised when ertapenem is used to treat these individuals. Future prospective studies to further evaluate risk and to derive a prediction scoring system may help to reduce the incidence of neurotoxic adverse events with ertapenem use. Disclosures All authors: No reported disclosures.