Close this search box.

A Comprehensive Guide to Sterility Testing of Parenterals

Sterility Testing of Parenterals

As a pharmaceutical manufacturer, the one thing you should never do is compromise on safety or quality. Not for the sake of cost-cutting. Definitely not for convenience. And not for any other reason. While quality and safety are ensured by well-designed, controlled and monitored production processes, these features are assessed using different testing techniques, with our focus today being on sterility testing of parenterals.

Before we dive into the what, when and how of the process, though, let’s take a look at the context within which sterility testing of small volume parenterals and large volume parenterals becomes of utmost importance.

Ever so often, the US FDA flags potential contamination of pharmaceutical products like tablets, eye drops, or syrups. The news is also often peppered with updates of product recalls by pharma companies. While such actions are important to take potentially harmful products off the market, naturally, you don’t want to end up in either of these situations yourself. It is not worth the loss of resources, reputation, or the health of the people who trusted you by purchasing and using your product.

This is why minimizing contamination, microbial and otherwise, is non-negotiable while producing drugs. Good manufacturing practices (GMP) guidelines outline how drug manufacturers can adapt appropriate quality assurance and management concepts to their production lines to meet stringent requirements and high standards in sanitary industries. Such guidelines are concerned with not only the pharmaceutical inputs and products themselves, but all involved materials including process equipment and packaging. Not to mention the training and hygiene of the personnel who handle the pharmaceutical production process. Sterility testing of large volume parenterals, small volume parenterals and other sterile products are critical parts of the quality control process, but it is in the implementation of parenteral manufacturing, storage, and packaging where all the magic really happens.

What are parenterals?

Now that we have some background, let’s break down the technical aspects that underlie sterility testing of parenterals. To begin with, we should explore what exactly parenterals are in the first place.

Simply put, any pharmaceutical product which makes its way into your body without going down your digestive tract is a parenteral. This means that any pills you pop or syrups you consume aren’t parenterals. But most vaccines, eye drops, and IV infusions are. These can be administered in a number of ways – intramuscular, intravenous, subcutaneous, and intraocular routes of administration are some of the ways in which parenterals are given to patients. And this just increases the need for sterility.

Parenterals are injected or implanted directly into your blood, skin, muscles, or other tissues. Since they make their way directly to your organs or bloodstream, bypassing most of your body’s external protective mechanisms, any contamination can have disastrous effects on your health. So you can see why sterility testing of parenterals is so critical.


The difference between small volume parenterals (SVPs) and large volume parenterals (LVPs)? It’s simple.

SVPs are parenterals packed in containers of volume 100 ml or less. Think pre-filled syringes, squeezable eye drop containers, vials, ampoules. They’re generally between 1 ml and 30 ml in volume, and are packaged as single or multiple doses.

LVPs, on the other hand, are packaged in volumes greater than 100 ml. Think IV bags. Almost always, they’re packaged as single doses.

What is sterility?

Sterility refers to the absence of bacteria or other microorganisms. As defined by international pharmacopoeiae, a specimen of a parenteral would be considered sterile only when it is absolutely and completely free of microorganisms. However, the definitions and measures of sterility are different for certain parenterals, for instance, biological drugs, for obvious reasons.

Universal tests

Sterility testing of parenterals is only one part of a bigger, more detailed picture. The United States Pharmacopoeia, or USP, defines several universal tests that should be applied to parenterals to assess their safety and quality. There are tests for identification, strength, impurities – chemical and physical (including visible foreign and particulate matter), bacterial endotoxins, container-closure integrity, and labelling. In addition to such universal tests, there are specific ones for uniformity, vehicles, added substances, antimicrobial preservatives, aluminium content, and completeness and clarity of solutions. Most of these depend on the particular parenteral in question, so naturally, we cannot go into them in detail here. But sterility testing of large volume parenterals and sterility testing of small volume parenterals are more or less universally applicable.

Sterility testing of parenterals

Sterility testing of parenterals is either carried out by the drug manufacturer or outsourced to a certified contract lab. All eye drops, creams, ointments, aerosols and the like are required to undergo sterility testing as per the standards outlined in the USP <71>, European Pharmacopoeia 2.6.1, Japanese Pharmacopoeia 4:06, and WHO (QAS / 11,413).

Measures to prevent contamination during testing

During sterility testing of parenterals, it’s possible that while drawing or transferring a sample, you may introduce a microorganism which wasn’t already present in the drug product. Neither false positives nor false negatives are desirable, so you have to rely on a number of measures to prevent such contamination. These measures involve personnel, testing equipment, the test environment, and appropriate controls.

Sterility testing of small volume parenterals as well as LVPs is performed in a controlled environment under aseptic conditions – this may be either an isolator which meets the requirements of an EU cGMP Grade A cleanroom or it could be a laboratory Grade A cleanroom which is surrounded by a Grade B cleanroom. Methods which don’t interfere with the protection of the cleanroom area are used to monitor the environmental conditions; this could be active air sampling with appropriate equipment. In critical areas like filling lines and isolators, gelatin membrane filters are used to detect viruses and other micro organisms in the process of air monitoring.

Appropriate validation procedures like bacteriostasis and fungistasis tests also need to be adopted to prevent the growth of any microorganisms in the samples being tested. And critically, well-trained personnel are indispensable. Overall, process risks must be weighed cost benefits while settling on a system for sterility testing of parenterals.

Something to keep in mind

As it stands, sterility testing is a destructive process. By virtue of extracting a sample and running it through different equipment and processes to test it, the product’s sterility is lost. You can’t administer it to a patient. This is why following GMP guidelines diligently is so important. Quality is baked into the production process itself; quality testing is only an added safeguard to catch lapses that may have otherwise gone undetected. Instead of testing every sample, sterility testing of parenterals is conducted on a few samples from every batch, selecting samples which would represent the entire batch as well as possible. Ideally, you would pick samples produced at the beginning, the middle, and the end of the batch. You should also pick samples produced right after a change in process, process equipment, after sterilization, or after any other modification is introduced into the system.

And most importantly, all this testing must be accompanied by documentation. If a tree falls and no one hears it, did it even fall? The same principle applies to quality control. You absolutely must keep records of the temperature, humidity, pressure and microbial presence conditions under which production took place. In addition to environmental monitoring data and simulation trail records, you should also keep validation documentation at hand for future reference for yourself and for regulators.

Before you test

GMP guidelines may vary by country, region, product or process. Make sure you’ve gathered all the specific requirements which apply to you before you get started producing or testing your product. For instance, sterility testing is performed with two culture media and two test containers in most countries. In China, however, sterility testing of parenterals must involve a three-container variant. Make sure you are aware of the nitty-gritties of the process as early as possible.

The method

Whether you’re involved in sterility testing of large volume parenterals or SVPs, there are generally two broadly-used methods. The method of culturing micro organisms to test product sterility has been around for close to a hundred years.

The method currently preferred by USP <71> and EP 2.6.1 is membrane filtration, at least when the nature of the product allows it. In this technique, antibiotics and other growth-inhibiting substances are washed out by pumping rinsing fluid (as specified by USP <71>) through the system. A peristaltic pump, or a cleanroom-suitable pressure supply is needed; this pump conveys the parenteral being tested into the sterility test units. Here, it is filtered through an incorporated membrane which a nominal pore size of about 0.45μm. This membrane is relied on to retain micro organisms. This works well for most parenterals in liquid form, but if the product is in powder form, it is dissolved in an appropriate medium using appropriate techniques before the same process is applied to it.

Now what happens if this technique is not suitable for a particular pharma product? In that case, a process called direct inoculation of the culture medium is employed. The test containers are each filled with the appropriate culture medium. This is generally casein soybean digest, or CASO, for the detection of aerobic bacteria and fluid thioglycolate for the detection of anaerobic bacteria.


As mentioned earlier, documentation or record-keeping is extremely important to prove that your work is GMP-compliant. Batch traceability for all products used and the sterility system itself shows that you are a reliable pharma manufacturer.

As you venture into the world of parenteral manufacturing, you absolutely must understand the ins and outs of sterility testing of parenterals. This article was only an introduction to the central role of sterility testing of small volume parenterals and large volume parenterals in your operations. For a more comprehensive understanding of how these processes apply to your specific operation, reach out to our team of experts. When you come to us with your process or high purity-related challenges, you’re sure to find a listening ear and a problem-solving approach in our experts. Because with us, the challenge is always accepted.

Share this post:

For 20 years, we’ve been the go-to problem-solvers for high-purity and injectable process applications in the pharma and biopharma industry. We are relentless about continuous process improvement and upskilling, elevating ourselves and our technology so you can get the job done more efficiently with cost optimisations. Use the form below to schedule a call back from our team.

This field is for validation purposes and should be left unchanged.