Level 2 Guidance for Pyrogen and Endotoxin Testing: Q&A Edition 2
In recent years, there’s been a lot of buzz about how companies test for bacterial endotoxins which essentially are harmful substances that can sneak into drugs and medical devices during manufacturing. Today we’re visiting the Food and Drug Administration’s (FDA) level 2 revision of the final guidance, “Pyrogen and Endotoxins Testing – Questions and Answers (Edition 2)”, released in March 2026 with the original publication in June 2012. The Questions and Answers (Q&A) help provide clarification to those issues that may be subject to misinterpretation, but note, not the entire subject of pyrogen and endotoxin testing is discussed in this Q&A. Let’s take a closer look!
The Bacterial Endotoxin Test, also known as the Limulus Amebocyte Lysate (or LAL) Test, is typically favored because of its sensitivity and reliability compared to the older rabbit-based Pyrogen Test. Both tests are recognized by official standards, but the LAL Test is used in many products due to its accuracy and ease of use. The LAL Test isn’t perfect; it can be affected by chemicals or the physical properties of the product being tested. Manufacturers are required to validate their testing methods for each type of product, making sure the results are accurate and reliable, even if they switch suppliers for the testing reagents [1] .
Sources of endotoxin contamination are variable such as water used in production, packaging materials, raw ingredients, and even equipment, can all introduce pyrogens. Removing endotoxins once they’re present is tough, so prevention is vital.
This guidance explains how companies should test their products to make sure they don’t contain pyrogens (fever causing substances) or endotoxins (toxins found in certain bacteria that can also cause serious adverse reactions).
Notably, in the revision, the FDA removed certain references to LAL testing to accommodate a broader scope of recombinant reagents. Sponsors using recombinant reagents should validate and verify that the assay method is suitable for its intended purpose. This action aligns with USP Chapter 〈86〉 Bacterial Endotoxins Test Using Recombinant Reagents published in May 2025. USP states, “This proposed new test chapter provides additional techniques using nonanimal derived reagents to the Bacterial Endotoxins Test 〈85〉. This general chapter is not currently being introduced into a specific monograph or listed in General Notices. It is the responsibility of the user to review the supplier’s primary validation package and to verify product suitability for use in testing specific products or materials. This verification must include specific experiments to confirm that the method is suitable for its intended purpose under the conditions of use for the material, drug substance, and/or drug product. The selected verification experiments should be based on an assessment of the complexity of the material to which the method is being applied.” The guidance revisions are consistent with the agency’s long-term goal to reduce, refine, and replace animal testing and provide flexibility for manufacturers to transition to the use of recombinant reagents for bacterial endotoxin testing of drugs and devices regulated by FDA [2] .
KEY POINTS TO CONSIDER [2] :
This document provides current FDA recommendations and considerations for testing pyrogens and endotoxins in pharmaceuticals, biologics, and medical devices, emphasizing methods, validation, sampling, and regulatory compliance.
Sampling must be appropriate, consider contamination risks, manufacturing design, process consistency, endotoxin removal steps, and product specifications. It should be dynamic, starting with maximum coverage and adjusting as confidence in process control increases. These sampling procedures should also be in the regulatory submissions with considerations for the raw materials, in-process materials, and finished products. Sampling should be adjusted based on process impact (e.g., hold times and removal steps) and all changes should be documented and submitted via supplements or reports.
Criteria for retesting and handling conflicting results are provided and all procedures must be pre-approved and documented.
Proper storage and handling are critical as they influence endotoxin detection. Procedures should be established based on stability data with considerations for source and native vs. purified endotoxins. Proper handling ensures assay accuracy and reproducibility.
Pooling is permitted for small-volume aqueous products and medical devices, with specific guidelines. For medical devices, rinsing/extracting techniques should be used per ISO standards.
Alternative methods are acceptable if validated and shown to be equivalent or superior to USP methods (i.e., validation must follow USP <1225>). Validation should include interference testing and detection accuracy with final decision defaults to USP gel-clot method unless specified.
Validation should address variability and manufacturing conditions when transitioning between endotoxin testing methods. For drugs/biologics, companies should submit a prior approval supplement or comparability protocol. For devices, a 30-day notice may suffice. Companies should maintain detailed validation data for FDA review.
The old limit table from 1987 is outdated; limits should be calculated per USP or AAMI standards.
Applying Quality by Design to endotoxin limits as it promotes the understanding of product and process to set justified endotoxin limits. Limits should be case-specific and justified in marketing applications.
The rabbit pyrogen test is required for certain biological products or if alternative methods are not demonstrated as equivalent. 21 CFR 610.13(b) may waive the requirement, if validated. Some USP monographs still mandate the requirement. It should be used if interference cannot be mitigated or non-endotoxin pyrogens are suspected.
Endotoxin limits for veterinary products are limited and determined based on multiple parameters; limits should be appropriate for multi-species use.
Endotoxin limits for medical devices depend on contact type and contact surface area, following USP <161>. Deviations from standards require premarket notification or approval.
For therapeutic products, undiluted product testing is preferred, testing should reflect the product formulation and potential interference.
Use of Control Standard Endotoxins (CSEs) are acceptable if traceable to international standards and properly calibrated. CSEs serve as calibration and control tools in endotoxin testing.
In summary, this FDA guidance helps manufacturers protect people by outlining clear expectations for testing. Companies should carefully review their procedures to align with the guidance, update their practices as more information becomes available to maintain patient safety as a top priority. Failing to do so poses health risks and leads to regulatory action and product recalls.
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