Understanding which antimicrobial agents are likely to be active against Gram-negative bacilli can guide selection of antimicrobials for empirical therapy as mechanistic rapid diagnostics are adopted. In this study, we determined the MICs of a novel β-lactam–β-lactamase inhibitor combination, imipenem-relebactam, along with ceftolozane-tazobactam, imipenem, ertapenem, meropenem, ceftriaxone, and cefepime, against 282 drug-resistant isolates of Gram-negative bacilli.