How to perform light-obscuration particle matter testing for injectables
What is particulate matter testing, and why is particulate matter testing important for injectable products?
Regarding particulate matter testing for injectables, the American USP aligns its guidelines with both the European and Japanese Pharmacopeia. Particulate matter refers to undissolved particles (other than gas bubbles) that are present in injectable solutions. This particulate matter is not an intentional addition to the parenteral formulation. Just as unintentional microbes in injectables are avoided and regulated to prevent patient illness, unintentional, non-biological particles are regulated in injectable formulations to prevent unwanted toxicity, disease, or side effects. For those creating parenteral products for veterinary use, solutions used for irrigation alone, or radiopharmaceutical preparations, particle matter regulation requirements of USP 788 do not need to be met. If your injectable product uses a filter before patient administration, your injectable may be exempt from particulate matter guidelines, provided supporting scientific data justify such an exemption. Note that this article will use parenteral and injectable synonymously. Thus, a small-volume injection and a small-volume parenteral are synonymous terms.
Particulate matter is detected using a light-obscuration particle count test and a microscopic particle count test. Light-obscuration particle count testing is preferred to detect subvisible particles in injections and parenteral infusions. However, parenteral preparations that have reduced clarity or increased viscosity (such as emulsions, colloids, and liposomal formulations) should be assessed using microscopic particle count testing. Microscopic particle count testing is also useful for products that tend to produce air or gas bubbles during sampling. In some cases, both particulate matter test methods will be needed to confirm subvisible particle counts. And select injectable formulations may be difficult to assay via both traditional particulate matter testing methods. In these select cases, often when the viscosity of the test preparation is high, a quantitative dilution with an appropriate diluent may be made to decrease viscosity, as necessary, to allow the particulate analysis to be performed.
How is particulate matter testing using light obscuration performed?
Light obscuration particulate matter testing uses a liquid particle counter machine that, based on the principle of light scattering, allows for an automated determination of the size of particles in a sample and the number of particles according to size. The liquid particle counter is calibrated using dispersions of spherical particles in particle-free water. These spherical particles are of known sizes between 10 microns (μm) and 25 μm. Before use, all glassware and testing equipment are rinsed with particle-free water. Samples of particle-free water are tested following equipment set-up to assure that no more than 25 particles of 10 μm or greater are identified in particle-free controls in replicate. If more particles are identified, the testing equipment will be cleansed again and recalibrated before sample testing.
For testing, each sample’s contents are mixed by slow inversion. Care is taken not to introduce air bubbles into examined preparations. Gas bubbles are further eliminated by allowing samples to stand for 2 minutes after inversion or through sonication. For small-volume Parenterals (less than 25 milliliters in volume), the contents of 10 or more units are combined in a cleaned container to obtain a volume not less than 25 milliliters (mL). Powders for parenteral use are reconstituted with particle-free water or an appropriate particle-free solvent when particle-free water is unsuitable. Injectables with a volume of 25 mL or more are tested individually. For pharmacy bulk packages “Not for Direct Infusion,” calculate the test result on a portion that is equivalent to the maximum labeled dose. For example, if the average particle count per mL is 5, you would multiply the particle count per mL by 10 to obtain the particle count for the 10-mL maximum dose. In this example, the particle count for the 10-mL maximum dose is 50. Products meant to hold a drug product and a solvent should be tested as directed for large-volume parenteral or small-volume parenteral products, depending on container volume.
The number of samples must be adequate to provide a statistically sound assessment. For injectables with a volume of 25 mL or more, less than 10 individual units may be tested.
After careful mixing, remove four portions, no less than 5 mL each, and count the number of particles equal to or greater than 10 μm and 25 μm. Calculate the mean number of particles for the preparation to be examined.
Once particles have been counted, calculate the mean number of particles for the sample examined. For light obscuration particle count tests, there are two test criteria. For sample preparations with a volume of more than 100 mL, the first test criteria apply. Samples with a volume of fewer than 100 mL use the second test criteria. The sample complies with the particle count test in the first test criteria if the average number of particles present in the units tested does not exceed 25 particles per mL equal to or greater than 10 μm and does not exceed 3 particles per mL equal to or greater than 25 μm. In the second test criteria, the sample meets the test criteria if the average number of particles tested does not exceed 6000 particles per container equal to or greater than 10 μm and does not exceed 600 particles per container equal to or greater than 25 μm. If the average number of particles exceeds the limits, test the samples by the microscopic particle count test.
Summary
Overall, particulate matter testing is a vital microbiology test for injectables. Unintentional, non-biological particles are regulated in injectable formulations to prevent unwanted toxicity, illness, or side effects in patients following treatment. Two tests can be used for particulate matter testing, a light-obscuration particle count test, and a microscopic particle count test. Light-obscuration particle count methods are used except when preparations are too cloudy or viscous for accurate particle detection. All in all, when developing your injectable product, ensure you choose a contract testing organization that can support you with appropriate microbiology testing for your unique medical device or product needs.
Ethide Labs is a contract testing organization that specializes in Microbiology Testing. Ethide Labs also offers Bioburden Testing, Environmental Monitoring, Sterilization Validations, Bacterial Endotoxin Testing, EO Residual Testing, Package Integrity Testing & Cytotoxicity Testing services for medical device companies and allied industries. Ethide is an ISO 13485 certified facility.
References
United States Pharmacopeial Convention. <788> Particulate Matter In Injections, In Vitro. Rockville, MD, USA. 2021. (USPC <788>).
