Guidance for Industry: Pyrogen and Endotoxins Testing: Questions and Answers
endotoxins used in the study, bearing in mind that purified bacterial endotoxins might react differently from native sources of endotoxins.
Yes. With some exceptions (see below), finished drug product units may be pooled into a composite sample and assayed for bacterial endotoxins. The composite sample may be represented by the entire unit or partial aliquots (equal volumes) of finished product containers from one manufactured lot of aqueous-based pharmaceuticals. Pooling would generally be accepted for small-volume parenterals (those with volumes of 100 mL or less) as long as the MVD is adjusted to a proportional, lower value because of the potential for diluting a unit containing harmful levels of endotoxins with other units containing lower, less harmful, levels of endotoxins. This “adjusted MVD” is obtained by dividing the MVD computed for an individual sample by the total number of samples to be pooled. FDA suggests pooling no more than three units per composite in keeping with the concept of testing representative beginning, middle, and end finished product containers. If this reduction in MVD results in an inability to overcome product-related assay interference because of an insufficient dilution, then the samples should be tested individually.
Some product types should not be pooled. Two examples are drug products that have an initial low MVD (see discussion above of “adjusted MVD”) and products that are manufactured as a suspension, because sample aliquot homogeneity may present significant interference issues. FDA also does not recommend pooling in-process samples from different in-process stages of the manufacturing process because it may be difficult to ensure the homogeneity of these materials.
Below are two examples of alternative assays.
Product-specific validation is necessary to establish whether a particular test substance or material is appropriate for evaluation of the monocyte activation method. The validation should include, but is not limited to, interference testing, accurate detection of pyrogen in individual test samples, and, for devices, ability of test system to provide direct contact to the monocytes.
way to establish the endotoxins limit is to use the calculation methods provided in the USP or AAMI standards. Monograph limits may also not account for current product strengths or dosage regimes; these should also be checked using the calculations recommended in the standards.
If there are several components in a finished product, then the overall endotoxins limit for parenterally-administered products should not exceed the overall threshold limit specified in the USP <85> Bacterial Endotoxins Test, regardless of an individual component endotoxins limit. Intrathecally-administered products, ophthalmics, or devices (see question 11 for devices) may have endotoxins limit requirements that are not based on the calculation for parenterally administered products. FDA encourages firms to check with the appropriate office or review division about these products.
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When implementing Quality by Design concepts, the strategy for endotoxins testing should be based upon product and process understanding in combination with risk management to ensure consistent final product quality. The appropriate in-process testing should be used to evaluate the production process areas at risk of endotoxins formation or incursion. Many firms already have programs for monitoring incoming ingredients and components, including the processing water, for endotoxins contamination. The finished product release specification should be considered when determining in-process limits for each phase of manufacturing tested. For purposes of evaluating the relative risk of product contamination, quantitative testing may be preferable to limit testing to facilitate product quality trending and to identify and correct excursions before they exceed the specification and cause product failure. An endotoxins limit should be justified on a case-by-case basis, and will be evaluated as a part of each relevant marketing application or supplement.
For certain biological products, 21 CFR 610.13(b) requires a rabbit pyrogen test. The requirement in 21 CFR 610.13(b) may be waived if a method equivalent to the rabbit pyrogen test is demonstrated in accordance with 21 CFR 610.9.
For human and animal drugs, some USP monographs still require a rabbit pyrogen test. Even with such monographs, a firm may substitute an endotoxins test or alternative cell-based test if the firm can demonstrate equivalent pyrogen detection. The appropriate FDA review division will consider alternative methods, such as monocyte activation, on a case-by-case basis.
For devices and drug materials, firms should assess the risk of the presence of non-endotoxin pyrogens. If the risk assessment indicates that non-endotoxin pyrogens may be present, it may be more appropriate to use the rabbit pyrogen test.
Bacterial endotoxins assays are subject to a variety of interferences related to the physical and chemical properties of the test article. Where such interferences cannot be mitigated through sample dilution (up to the MVD) or other validated means of sample preparation, firms should use the rabbit pyrogen test.
For a veterinary product labeled for use in multiple species, the limit should be based on the maximum product dose used on the smallest species. If the label indicates that the product may be used on juvenile and adult animals, the juvenile is considered the worst case. If the weight of the animal is required to calculate the dose, firms should use an average weight for that species. For a listing of some average animal weights, see the FDA draft guidance for industry on Waivers of In Vivo Demonstration of Bioequivalence of Animal Drugs in Soluble Powder Oral Dosage Form Products and Type A Medicated Articles. For animal weights not listed in that guidance, please contact FDA’s Center for Veterinary Medicine.
For medical devices, using the extraction volume recommendations described below, the limit is 0.5 EU/mL or 20 EU/device for products that directly or indirectly contact the cardiovascular system and lymphatic system. For devices in contact with cerebrospinal fluid, the limit is 0.06 EU/mL or 2.15 EU/device. For devices that are in direct or indirect contact with the intraocular environment, a lower endotoxins limit may apply. Please contact the appropriate review division for specific recommendations.
The process of preparing an eluate/extract for testing may vary from device to device. Some medical devices can be flushed, some may have to be immersed, while others may need disassembly. Unless otherwise directed by another compendial standard, our recommended rinse volumes include the following: (1) each of the 10 test units should be rinsed with 40 mL of non-pyrogenic water; (2) for unusually small or large devices, the surface area of the device that contacts the patient may be used as an adjustment factor in selecting the rinse or extract volume. The endotoxins limit can be adjusted accordingly. In any case, the rinse/extract procedure should not result in a greater dilution of endotoxin than recommended in USP <85>. For inhibition/enhancement testing, both the rinse/extract solution and the device eluate/extract should be tested.
Examples of medical devices with testing or interference challenges include devices that are coated with anticoagulant, contain heavy metals, or that have particulates. In these situations, treatments for interferences can include digestion, dilution, and addition of buffers, centrifugation, or filtration.
During the same surgical procedure or placement in the same surgical site, multiple units of the same device from one manufacturer should generally meet the same endotoxins limit as a single device administered during the procedure. In instances where multiple units of the same device are known or intended for use in a single procedure, manufacturers should justify any deviation from the overall endotoxins limit identified in this guidance.
When a manufacturer of medical devices plans to use LAL testing that deviates significantly from this guidance or recognized standard, a premarket notification (510(k)) under section 510(k) of the Federal Food, Drug, and Cosmetic Act (the Act) or a premarket approval application (PMA) supplement under section 515 of the Act should be submitted. Significant deviations include, but are not necessarily limited to: higher endotoxin concentration release criteria, sampling from fewer than three (3) lots for inhibition/enhancement testing, lesser sensitivity to endotoxins, and a device rinsing protocol resulting in greater dilution of endotoxins than that recommended in this guidance.
Ideally, the undiluted product should be screened as long as there is no interfering/enhancing property within the LAL test. However, in some product formulations, the ingredients interfere with the LAL test. For such formulations, the USP recommends that the product be diluted to overcome interference or enhancement properties. The calculated MVD is the dilution of a sample at which the endotoxins limit would be detected, but it should not be the regular testing dilution. When product interference is encountered during development, FDA recommends that the firm determine the lowest product dilution that would neutralize the interfering condition.
FDA recommends that firms begin subsequent product screening at a product dilution just above the level that neutralized the interference. For example, if the product has an MVD of 1:100, and the product displays inhibition at the 1:10, but not at the 1:20, it may be best to screen product at 1:30. If bacterial endotoxins are detected at this level, then the firm should conduct full enumeration with the product to titrate the true amount of endotoxins.
Control standard endotoxins (CSEs) are endotoxin preparations other than the international or national reference standards that are traceable in their calibration to the international reference endotoxins standard. CSEs may be secondary or tertiary standards and are usually manufactured and certified by an LAL reagent manufacturer for use with a specific lot of reagent under defined assay conditions. CSEs have become an accepted source for preparation of standard curve calibrators and as assay controls, and have provided a cost saving to LAL users and helped to preserve the inventory of primary standards. FDA encourages the continued use of CSEs that are suitably calibrated to the international reference endotoxins standard.
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