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# PhRMA Urges Changes to FDA’s ‘Plausible Mechanism’ Guidance
- URL: https://www.fdaweb.com/phrma-urges-changes-to-fdas-plausible-mechanism-guidance/
- Published: 2026-05-01T12:00:00.000Z
- Updated: 2026-09-14T13:38:28.000Z
- Author: David McFarland
- Tags: FDA Policy/General, #legacy-id-D5161079

The Pharmaceutical Research and Manufacturers of America (PhRMA) is urging FDA to broaden and clarify its draft guidance on individualized therapies, warning that overly narrow definitions and unclear expectations could hinder innovation in precision medicine. In [formal comments ](https://downloads.regulations.gov/FDA-2026-D-1256-0131/attachment%5F1.pdf?ref=fdaweb.com)submitted on the agency’s proposed “plausible mechanism” framework, PhRMA called for a more flexible, technology-agnostic approach that can accommodate emerging treatment modalities, including RNA and gene therapies. The group argued that FDA should reconsider the term “individualized therapies,” suggesting alternatives such as “targeted therapies” to better reflect the evolving science and avoid constraining future regulatory applications.

PhRMA emphasized that the framework should explicitly apply across therapeutic classes, including recombinant proteins, RNA-based treatments, and gene therapies beyond genome editing. It also cautioned against interpretations that could exclude certain products — such as siRNA therapies targeting multiple variants — without a clear scientific basis.

A central theme of the comments is the need for greater clarity. PhRMA urged the agency to provide concrete examples and case studies to illustrate key scientific and regulatory concepts, including what constitutes a “clear connection” between a genetic alteration and disease, a “robust” investigation, or a “well-characterized” natural history. The group noted that such terms are difficult to operationalize, particularly in rare disease settings where clinical trials often involve very small patient populations and traditional statistical methods may not be feasible.

To address these challenges, PhRMA encouraged the agency to recognize alternative forms of evidence — such as consistency across endpoints, durability of response, and mechanistic plausibility — as valid indicators of effectiveness. It also called for explicit acknowledgment of the role of real-world data and real-world evidence in supporting regulatory decisions, especially when conventional trials are impractical.

The industry group voiced strong support for the draft guidance’s proposal to allow expansion of approvals to additional genetic variants based on a shared mechanism of action. However, it flagged uncertainties around implementation, including how such expansions would be submitted — whether through supplements, amendments, or new applications — and how they would align with existing regulatory frameworks for investigational new drugs and biologics license applications.

PhRMA also highlighted potential inconsistencies between the draft guidance and prior FDA policies on the handling of multiple product variants, urging the agency to clarify when sponsors may include multiple versions within a single application versus separate filings.

On evidentiary standards, the group backed FDA’s flexible approach to confirmatory evidence but asked for more detailed guidance on statistical methodologies suitable for small populations. It recommended that the agency outline how mechanistic, biomarker-driven, and exposure-response data can support approvals under both traditional and accelerated pathways.

Beyond evidentiary issues, PhRMA called on the FDA to explain how the plausible mechanism framework will interact with existing expedited programs, including Breakthrough Therapy, Fast Track, and Regenerative Medicine Advanced Therapy designations. Clear alignment, it argued, is essential to provide predictability for sponsors and sustain investment in individualized treatments.

Finally, PhRMA urged FDA to ensure that chemistry, manufacturing, and controls (CMC) requirements remain proportionate to the stage of development. It warned that language in the draft guidance could be interpreted as imposing late-stage manufacturing expectations too early, potentially creating barriers for novel therapies, particularly in areas like cell and gene therapy where data may be limited.