If considering eravacycline or imipenem/cilastatin/relebactam, when should you ask for an E-test?

• A. On the front end for a known multidrug-resistant pathogen
• B. Only after therapy has started
• C. Never use E-test for these agents
• D. Only in research settings

Answer: (A)

The main idea is using MIC testing to guide therapy for known multidrug-resistant pathogens. An E-test gives a precise MIC value for a specific antibiotic-pathogen combination, so ordering it up front helps confirm whether eravacycline or the imipenem/cilastatin/relebactam combo is likely to work and informs proper dosing. When a resistant organism is already identified, having that MIC early supports rapid, targeted treatment and stewardship decisions, reducing the risk of starting an ineffective regimen. Waiting to test after therapy has begun delays crucial adjustments and may lead to suboptimal outcomes. These tests are used clinically, not just in research, and there are valid, patient-centered reasons to obtain an E-test result at the outset for known MDR pathogens.