Antibacterial Susceptibility Test Interpretive Criteria

Why It Matters

Clinicians and clinical labs rely on FDA‑endorsed STIC to interpret susceptibility results, influencing treatment decisions and antimicrobial stewardship. Without recognized criteria, laboratories face uncertainty, potentially affecting patient outcomes and regulatory compliance.

Key Takeaways

• FDA aligns with CLSI 2026 M100 for most antibacterial breakpoints
• Some drugs, like amikacin, have both STIC and FDA exceptions
• Drugs marked * lack any FDA‑recognized susceptibility criteria
• Recognition covers surrogate testing methods for listed drug‑bacteria combos
• STIC recognition does not guarantee clinical efficacy or labeling approval

Pulse Analysis

Antimicrobial susceptibility testing (AST) is a cornerstone of modern infectious‑disease care, translating laboratory data into actionable treatment choices. By officially recognizing the Clinical and Laboratory Standards Institute (CLSI) performance standards—most notably the 2026 M100 supplement—the FDA provides a unified framework that laboratories can trust for breakpoint interpretation. This alignment reduces variability across testing sites, streamlines regulatory reporting, and supports consistent antimicrobial stewardship programs that aim to curb resistance.

The FDA’s table of recognized susceptibility test interpretive criteria (STIC) offers granular detail: the majority of injectable and oral antibiotics are covered, but several agents—identified with an asterisk—still lack any FDA‑endorsed breakpoints. For those drugs, clinicians must rely on alternative guidance, such as pharmacodynamic data or international standards, which can introduce uncertainty. Moreover, the agency’s explicit exclusion of epidemiological cutoff values (ECVs) underscores that STIC focuses on clinical breakpoints rather than microbiological susceptibility trends, a distinction critical for both drug developers and diagnostic manufacturers.

For the industry, this FDA‑CLSI partnership signals a stable regulatory environment while highlighting gaps that may become opportunities for future standard development. Companies developing new antibiotics or combination therapies can anticipate the pathway to STIC recognition, leveraging the documented exceptions and additions as a roadmap. Meanwhile, clinical laboratories benefit from clear, authoritative references that simplify compliance and improve the reliability of susceptibility reports, ultimately enhancing patient care across the United States.