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USP Sterility Testing for Pharmaceuticals and Medical Devices
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Summary
USP <71> sterility testing is a microbiological method used to confirm that pharmaceutical products, medical devices, and biologics are free from viable microorganisms. Results are qualitative and reported as pass or fail. These results are accepted by regulators such as the FDA and EMA for the release of sterile products. The test uses membrane filtration or direct transfer methods, supported by growth promotion and method suitability studies.
Quick understanding of the test
USP <71> - Sterility testing of Pharmaceutical Products
USP 71 is applied to various products, including pharmaceuticals, medical devices, biologics & radiopharmaceuticals.
- Staphylococcus aureus (ATCC 6538)
- Bacillus subtilis
- Pseudomonas aeruginosa
- Clostridium sporogenes
- Candida albicans
- Aspergillus niger
- Test samples are filtered through a membrane under sterile conditions.
- The filtered membrane is then transferred to appropriate growth media.
- The inoculated media are incubated for a period of 14 days.
- After incubation, microbial growth on the membrane is analyzed
Direct Transfer Sterility Testing – In this method, sample products are transferred into Fluid Thioglycollate Medium (FTM) and Soybean Casein Digest Medium (SCDM).
Cultures are incubated for 14 days. Microbial growth is monitored through periodic observations during the incubation period.
- Ensures that products intended for medical use are sterile and safe
- Provides a reliable method to monitor and control microbial levels in pharmaceutical manufacturing.
Turnaround Time
Passing criteria
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What is USP Sterility Testing?
USP <71> Sterility Testing is a standardized method defined by the United States Pharmacopeia used to determine whether a pharmaceutical product, medical device, or biologic is sterile. The test is designed to detect microbial contamination that could pose a serious risk to patient safety, especially for products intended to be sterile at the point of use.
The United States Pharmacopeia (USP) 71 specifies the guidelines on how products can be tested for sterility and the criteria for acceptance to ensure that pharmaceutical products are free of microbial contamination. Manufacturers need to follow these guidelines to ensure that the quality of their products is high and meets the GMP requirements.
Unlike bioburden testing, which estimates the number of microorganisms present, USP <71> focuses on the presence or absence of viable organisms. It is therefore a pass/fail test and is considered one of the most critical quality control requirements for sterile products.
USP Regulatory Relevance
USP <71> is widely recognized by global regulatory authorities as the standard sterility test for finished products.
FDA
The US FDA requires USP <71> sterility testing for testing sterile pharmaceuticals, biologics, and medical devices marketed in the United States.
EMA
The European Medicines Agency accepts USP <71> as an equivalent sterility test method, alongside Ph. Eur. 2.6.1. Manufacturers supplying products to the EU often rely on USP <71> data to support sterility claims and regulatory submissions.
GMP relevance
USP <71> is an important part of Good Manufacturing Practice. It supports batch release decisions, process validation, media fill qualification, and ongoing sterility assurance programs.
Purpose of USP Sterility Test
The primary purpose of USP <71> testing is to verify that a product labeled as sterile is free of viable microorganisms. This verification is essential to ensure –
- Protect patient safety
- Support batch release of sterile products
- Validate aseptic manufacturing processes
- Meet regulatory and pharmacopeial compliance requirements
Products Covered Under USP
USP <71> applies to a wide range of sterile products across pharmaceutical and medical sectors.
Pharmaceuticals
- Parenteral products (injectables, infusions)
- Ophthalmic preparations
- Sterile powders and lyophilized products
- Inhalation solutions
Medical Devices
- Implantable medical devices
- Surgical instruments labeled as sterile
- Catheters, syringes, and single-use disposables
- Wound care and dressing products
Biologics & Radiopharmaceuticals
- Vaccines
- Cell and gene therapy products
- Blood-derived products
- Radiopharmaceuticals with short shelf life
Test Organisms suitable for Growth Promotion and Method Suitability tests
- Aerobic Bacteria – Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa
- Anaerobic Bacterium – Clostridium sporogenes
- Fungi – Candida albicans, Aspergillus niger
USP <71> Sterility Testing Test Methodology
Membrane Filtration Method
This method is applicable for aqueous, oily, and alcoholic formulations, including products that are either soluble or capable of forming stable emulsions.
Procedure
- The membrane filter (nominal pore size โค 0.45 ยตm) to be used is sterilized and the filtration apparatus is assembled under aseptic conditions.
- The product is passed through the filter
- Post filtration, the membrane is incubated in suitable growth medium for 14 days.
- Fluid Thioglycollate medium – Anaerobes
- Soybean-Casein Digest medium – Aerobes and Fungi
- After 14 days, the results are observed and recorded.
Direct Transfer Sterility Testing
This method is suitable for products that cannot be filtered, like ointments, suspensions, bulk solids, or certain medical devices.
Procedure
- A specified quantity of product is directly added to the culture media making sure that the volume of product is 10% of total media volume.
- If the product has antimicrobial properties, neutralisers are added.
- The inoculated culture media is then incubated for at least 14 days and the growth is observed.
Why Growth Promotion and Method Suitability Tests are Critical in USP Testing?
Growth Promotion Test (GPT):
The Growth Promotion Test verifies that the culture media used in USP <71> sterility testing supports the growth of test microorganisms. This step is crucial to confirm the performance and sensitivity of the test media to ensure reliable detection and enumeration of test microorganisms. Since sterility testing is a negative test, validating that the media can promote microbial growth ensures that a โno growth observedโ result is valid and not because the media failed to support microbial growth.
Method Suitability Test:
The Suitability Test confirms that the product when undergoes testing does not inhibit microbial growth or interfere with microbial detection. Certain formulations contain antimicrobial or preservative components that could suppress microbial recovery and lead to false-negative results. If suitability test confirms that the product shows inhibitory effect, neutralizers are added to make sure it doesnโt affect the results during the sterility test. Hence, this assessment ensures that the sterility method is reliable, product-specific, and capable of detecting any viable contamination present.
Results Interpretation & Acceptance Criteria
USP <71> sterility testing is qualitative.
- Pass: No evidence of microbial growth observed in either medium after the specified incubation period
- Fail: Any visible microbial growth detected
A failed sterility test triggers a formal investigation, including laboratory assessment, manufacturing review, and potential batch rejection.
USP vs Bioburden Testing
Although both tests relate to microbial control, they serve different purposes.
USP <71> confirms the absence of viable microorganisms in finished sterile products. Bioburden testing, on the other hand, quantifies the microbial load present before sterilization and supports sterilization validation.
When to Choose Membrane Filtration vs Direct Transfer
Membrane filtration is recommended when the product is filterable and does not clog or damage the membrane. It offers higher reliability and sensitivity.
Direct transfer is chosen when filtration is not feasible due to product formulation, physical form, or low sample volume.
The final method selection must be justified through method suitability testing.
Limitations of Sterility Testing
Despite its importance, USP <71> has inherent limitations.
Negative test
A negative result does not guarantee absolute sterility. It only indicates that no microorganisms were detected in the tested samples.
Statistical sampling
Sterility testing is based on limited sample sizes. Contamination present in untested units may go undetected.
For this reason, sterility testing must be supported by robust aseptic controls and environmental monitoring.
Common Reasons for USP Failure
- Inadequate aseptic processing
- Environmental contamination during manufacturing
- Product-related microbial inhibition masking growth
- Laboratory handling errors
- Compromised container closure integrity
Identifying the true root cause is critical for regulatory compliance and corrective action.
Comparison with Other Similar Test Standards
Aspect | USP <71> Sterility Test | ISO 11737-2 Sterility Test |
Purpose | To confirm absence of viable microorganisms in finished sterile products | To demonstrate sterility of medical devices after sterilization. |
Regulatory acceptance | Accepted by FDA, EMA, and other global regulators | Widely accepted for medical devices, especially in ISO-regulated markets |
Scope of Products | Pharmaceuticals, biologics, and medical devices | Medical devices only |
Test outcome | Qualitative (pass or fail) | Qualitative (pass or fail) |
Typical use | Batch release and regulatory submissions | Sterilization validation and routine sterility testing for devices |
Importance of USP <71> Sterility Testing
Sterility testing is important in ensuring the safety of patients. Infections and complications caused by contaminated products could prove to be severely dangerous to immunocompromised patients. It ensures pharmaceutical products and medical devices meet the highest standards of safety before they are released to the market. It also plays a role in validating the manufacturing process by indicating any weaknesses in their aseptic techniques or their methods of sterilization.
Why Choose Our Lab for USP Testing
MIS performs sterility testing of pharmaceutical products using both direct transfer and membrane filtration methods. With extensive experience in research and analysis, our specialists are at the forefront of quality assurance. Additionally, in our testing lab, we have the full capacity to do the USP 51 Preservative Challenge test.
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Frequently Asked Questions
DR. Martinoz Scholtz
The main methods are membrane filtration and direct inoculation. The choice of method depends on the productโs nature and formulation.
USP <71> sterility testing evaluates the efficacy of products labeled as โsterileโ to ensure safety and compliance with good manufacturing practices.
The two methods used in USP <71> are:
- Membrane Filtration for filterable products
- Direct Inoculation (Direct Plating) for non-filterable products.
A 14-day incubation allows sufficient time to detect slow-growing microorganisms in the culture media before concluding sterility.
USP <71> is a recognized method for sterility testing under FDA regulations, but specific regulatory requirements depend on product type and other validated methods may also be acceptable.
No, sterility testing checks finished units for contamination, but aseptic process validation is a separate method to show that the manufacturing process consistently produces sterile products.
A sterility test failure triggers a formal investigation to identify the root cause. This includes laboratory assessment, manufacturing review, and evaluation of aseptic controls, and may result in batch rejection or corrective actions.
The standard is designed to detect a wide range of microorganisms, including bacteria (both aerobic and anaerobic) and fungi.
Yes, sterility testing is applicable to medical devices that require sterility, such as implants and surgical instruments.
Yes, radiopharmaceuticals can be tested using this standard. However, additional precautions may be necessary due to their radioactive nature.
Bioburden testing measures the total number of viable microorganisms on a non-sterile product, while sterility testing confirms the absence of viable microorganisms in products intended to be sterile.
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