OBJECTIVES: Outpatient parenteral antimicrobial therapy (OPAT) with carbapenem for bacteraemia caused by extended-spectrum beta-lactamase (ESBL)-producing bacteria may potentially be cost-saving. Yet in Hong Kong, China and many southeast Asia regions, patients requiring intravenous antimicrobial therapy are usually treated in an in-patient setting. In the present study, we analyzed the cost of inpatient versus outpatient carbapenem treatment for ESBL bacteraemia. METHODS: Economic outcomes of two antimicrobial strategies were simulated by a decision tree: 1) inpatient carbapenem treatment; 2) outpatient group (initially inpatient carbapenem treatment followed by ertapenem OPAT). Clinical inputs were estimated from literature and cost analysis was conducted from Hong Kong public health care provider’s perspective. Robustness of model was examined by sensitivity analysis. RESULTS: The results showed that outpatient group (US$12,008) was less costly than the inpatient group (US$15,446) (USD1=HKD7.8) by 22% in base-case analysis. The model was robust to variation of all variables in one-way sensitivity analysis. In Monte Carlo stimulations, cost of outpatient group (US$13,153 ± 2,064) was significantly lower than the inpatient group (US$15,650 ± 1,602) 98.6% of the time by a mean difference of US$2,497 (95% CI = US$2,469-2,525) (p<0.0001). CONCLUSIONS: Initial inpatient carbapenem treatment followed by OPAT appears to be less costly than an inpatient treatment course for ESBL bacteraemia from the perspective of Hong Kong public healthcare providers.