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Sterility – Stasis Test: Purpose, Procedure, and Interpretation as per GMP Guidelines

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Sterility testing is one of the most critical microbiological tests in the pharmaceutical industry, designed to confirm that sterile drug products are free from viable microorganisms. To ensure reliability of the sterility test results, a Stasis Test (also known as a Hold Time or Incubation Hold Test ) is performed as part of method validation. The Stasis Test confirms that the sterility testing system, media, and environment remain sterile during the pre-incubation or hold period before the actual test begins. What Is a Sterility Stasis Test? The Stasis Test is a microbiological control step conducted to verify that the test system remains sterile during the interval between the completion of test setup and the beginning of the incubation period. It is essentially a pre-incubation holding validation carried out to demonstrate that the sterility test environment, transfer process, and media are not compromised by any contamination. Purpose of the Stasis Test The mai...
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Sterility Test – When the Product Renders the Medium Turbid: Root Cause, Investigation, and Preventive Actions

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Sterility testing is one of the most critical microbiological quality control procedures in the pharmaceutical industry. It ensures that sterile products—such as injectables, ophthalmic solutions, and biological preparations—are free from viable microorganisms. However, sometimes during testing, the sterility test medium becomes turbid even in the absence of microbial contamination. This condition, often described as “product renders the medium turbid” , can lead to false-positive results and unnecessary investigations if not correctly identified and justified. Understanding Turbidity in Sterility Test Medium The sterility test medium—such as Fluid Thioglycollate Medium (FTM) and Soybean Casein Digest Medium (SCDM) —is normally clear and transparent before incubation. Turbidity in the medium is typically interpreted as microbial growth, which signifies contamination. However, certain product formulations can cause the medium to appear turbid even when sterile, due to c...
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Sterility Test Diluent vs Routine Injection Diluent — Why Product-Specific Mimic Fluid Is Critical for Reliable Results

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Sterility testing is a critical quality control step in pharmaceutical manufacturing that ensures sterile products remain free from viable microorganisms. A key element influencing test accuracy is the choice of diluent or vehicle fluid used during the test. While some laboratories use the routine injection diluent during sterility testing, this practice can lead to inaccurate or misleading results. Regulatory authorities and GMP guidelines clearly emphasize that the sterility test diluent must mimic the actual product formulation to reflect real manufacturing and aseptic conditions. Understanding the Role of Diluent in Sterility Testing In a sterility test, especially when using the membrane filtration method or direct inoculation method , a diluent is often required to dissolve, suspend, or dilute the product sample before transferring it into the test medium. The diluent plays a crucial role in ensuring that: The product is evenly distributed in the test system....
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Sterility Test Failure Investigation — Practical Examples and Lessons Learned

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Sterility testing is one of the most critical quality control procedures in pharmaceutical microbiology. It ensures that parenteral, ophthalmic, and other sterile products are free from viable microorganisms. However, when a sterility test failure occurs, it raises serious questions about the integrity of the aseptic process, product quality, and GMP compliance. This article explains how to investigate sterility test failures through detailed, real-world examples and provides essential lessons learned for avoiding future occurrences. What is a Sterility Test? A sterility test is designed to demonstrate that a product or batch is free from viable microorganisms. It is performed using validated methods such as: Membrane Filtration Method: Preferred for aqueous and filterable products. Direct Inoculation Method: Used for oily, viscous, or non-filterable samples. The test follows pharmacopeial standards such as USP <71> , Ph. Eur. 2.6.1 , and IP 3.2.1 , and...
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Aseptic Process Simulation Failure — How It Impacts Sterile Product Manufacturing and How to Prevent It

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In sterile product manufacturing, aseptic process simulation (APS) —also known as media fill —is a critical validation tool that verifies the capability of the aseptic process to produce sterile products without contamination. However, when a media fill failure occurs, it indicates a potential weakness in aseptic technique, facility design, or environmental control. This article provides a detailed understanding of aseptic process simulation failures , their impact on sterile product manufacturing, root cause analysis, and preventive strategies in compliance with GMP, WHO, and FDA regulations . What is Aseptic Process Simulation (Media Fill)? Aseptic Process Simulation (APS) or media fill is a validation exercise designed to simulate the actual aseptic manufacturing process using a sterile nutrient medium instead of the product. Its purpose is to demonstrate that the aseptic process, personnel, and environment can consistently produce a sterile product. Objective: T...
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Sterility Test Troubleshooting: Common Problems and Effective Solutions

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Sterility testing is one of the most critical quality control activities in the pharmaceutical and biotechnology industries. It ensures that sterile drug products, medical devices, and injectable formulations are completely free from viable microorganisms. However, due to the highly sensitive and aseptic nature of the process, sterility testing can face unexpected challenges or test failures. This detailed guide focuses on sterility test troubleshooting — identifying common issues, their root causes, and effective solutions as per GMP, WHO, and USP guidelines . What is Sterility Testing? Sterility testing is a microbiological examination designed to detect the presence of viable microorganisms in sterile products. It is performed under aseptic conditions using validated methods such as: Membrane Filtration Method – Preferred for filterable products like injectables. Direct Inoculation Method – Used for non-filterable or oil-based products. The methods are descr...
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Sterility Test Common Audit Findings: GMP Compliance and Best Practices

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Sterility testing is one of the most critical quality control procedures in the pharmaceutical and biotechnology industries. It verifies that sterile drug products and medical devices are free from viable microorganisms. However, during GMP inspections or audits, sterility test-related non-compliances are among the most frequently reported findings. Understanding these audit observations and implementing preventive actions is essential for maintaining product quality and regulatory compliance. What is Sterility Testing? Sterility testing is performed to confirm that the product is free from viable microorganisms. The test is mandatory for sterile dosage forms such as injections, ophthalmic preparations, and implantable devices. It is performed under aseptic conditions using validated methods outlined in: USP <71> – Sterility Tests European Pharmacopoeia (Ph. Eur.) 2.6.1 – Sterility Indian Pharmacopoeia (IP) 3.2.1 – Sterility Test WHO TRS 961 Annex 6 ...
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