21 CFR 610.13 Purity and Pyrogen Testing Requirements

Under 21 CFR §610.13, all licensed biological products in the United States must be free of extraneous material and non-toxic, meeting generally accepted standards of purity and quality.
Section 610.13(b) specifically requires that each lot of a licensed biological product intended for injection be tested for pyrogenicity before release.

In modern biologics regulation, §610.13 functions as a core purity safeguard, ensuring that both visible and subvisible impurities, as well as pyrogenic substances, are controlled through validated manufacturing and testing processes.

Regulatory Significance: Applies to all licensed biologics under 21 CFR Part 610.

Enforces purity and safety by requiring products to be free of extraneous material except that which is unavoidable by good manufacturing practice (GMP) and explicitly approved as part of the BLA.

Requires pyrogen testing for injectable products to prevent fever or inflammatory responses caused by bacterial endotoxins or non-endotoxin pyrogens.

Key Points

Purity Standard: No extraneous material is permitted unless unavoidable and approved by FDA as part of the BLA.

Manufacturing Controls: Processes must be validated to prevent contamination and minimize impurities.

Pyrogen Testing (§610.13(b)):

Historically required the Rabbit Pyrogen Test (USP <151>).

Modern practice allows alternative validated methods under §610.9 — typically the Bacterial Endotoxins Test (BET, USP <85>), based on the Limulus Amebocyte Lysate (LAL) or recombinant factor C (rFC) assay.

BET is preferred due to its higher sensitivity, speed, and elimination of live animal testing.

If non-endotoxin pyrogens are a concern, the RPT may still be required.

Regulatory Review: All unavoidable residuals and validated pyrogen testing methods must be justified and documented in the BLA.

Practical Impact for Manufacturers

Compliance with §610.13 requires:

• A risk-based impurity and pyrogen control strategy.

• Characterization and justification of any unavoidable residuals.

• Demonstration of process consistency and control of pyrogenicity throughout manufacturing and release testing.

• Alignment with compendial methods such as USP <71> (Sterility Tests), USP <85> (Bacterial Endotoxins Test), and USP <151> (Rabbit Pyrogen Test).