News: Rapid AST shows no clear benefit in gram-negative bacteremia, study finds

In a multinational randomized trial, rapid antimicrobial susceptibility testing (AST) shorted the time to antibiotic modification in patients with gram-negative bacteremia, but did not improve the primary outcome of desirability of outcome ranking (DOOR) at 30 days compared with standard testing.

Researchers conducted an open-label randomized clinical trial of 850 patients spanning all age groups with gram-negative bacteremia from 2023 to 2025 across Greece, India, Israel, and Spain. Patients were randomly assigned to undergo rapid AST plus standard susceptibility testing or standard susceptibility testing alone.

The primary endpoint was DOOR, categorized as alive with deleterious events, alive with deleterious events or death, at day 30. Deleterious events included poor clinical outcomes such as failure to discharge, infection relapses or complications, kidney failure, or acquisition of hospital-acquired multidrug-resistant infections.

The probability of more favorable DOOR outcomes with rapid versus standard AST was 48.8%. This did not meet the prespecified criterion of a lower limit for superiority. All-cause 30-day mortality rates were similar between the rapid AST and standard AST groups with no significant differences in hospital stay, ICU admission, acquisition of multidrug-resistant organisms, or time to effective antibiotic therapy within three days. Patients in the rapid AST group underwent antibiotic escalation or deescalation 14 hours earlier than those in the standard testing group.

Among patients with carbapenem-resistant infections, fewer patients in the rapid AST arm than in the standard AST arm remained hospitalized at day 30. The median time to effective therapy was shorter with rapid AST than with standard AST.

Editor’s note: To read the full study, click here. to read additional coverage by Medscape, click here.