How to properly condition gel packs for pharmaceutical and vaccine shipping

PCMs and gel packs are ideal for transporting temperature-sensitive products, but there is a process to prepare them.

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Well-conditioned gel packs can be a cost-effective and valuable solution to safely ship temperature-sensitive items like pharmaceuticals, vaccines, or biologics in passive containers. However, when using gel packs, they must maintain a constant temperature throughout the entire shipping process regardless of external fluctuations. An increase or decrease in temperature of only 2 degrees Celsius can greatly diminish a product’s potency or even spoil it altogether. Accordingly, let’s review the best ways to condition gel packs and provide details on how to get the most out of them.

Gel packs (aka coolants, refrigerants, PCMs, and ice packs) are leak-proof containers designed to maintain the recommended cold chain temperature range inside a cold box or vaccine carrier. Gel packs are used in four ways:

  • Frozen solid gel packs are taken directly from the freezer and generally frozen between 20 degrees Celsius and minus-25 degrees Celsius. When added to a passive container, the container’s temperature will drop to well below 0 degrees Celsius and remain there for several hours. Although they stay cold, frozen gel packs should not be used to transport temperature-sensitive products, such as pharmaceuticals, vaccines, or biologics.
  • Conditioned gel packs are warmed or thawed at room temperature until melted and start to liquefy. This change usually occurs at around 0 degrees Celsius. If done correctly, this process removes the initial freezing risk without significantly reducing cold life.
  • Cool gel packs are kept in a refrigerator and not frozen. This removes the freezing risk but lacks the cooling performance and protection that a frozen gel pack offers.
  • Warm gel packs remain at room temperature and are typically used in extremely cold climates to prevent damage to freeze-sensitive vaccines. This article will strictly focus on frozen and conditioned gel packs. After selecting a gel pack type and observing its temperature requirements, it is imperative that you duly freeze it and then condition it to maximize effectiveness.

A properly conditioned gel pack can prevent the product from freezing when in a vaccine carrier. With that noted, you may need your gel pack to be frozen or refrigerated.

Conditioning Frozen Gel Packs

If you require frozen units, prepare the gel pack in a sufficient-sized freezer that can cool at 0 degrees Celsius and ultimately settle between minus-18 degrees Celsius and minus-20 degrees Celsius. Using this method eliminates the initial risk of thermal shock without reducing the amount of time it can stay cold. It’s important to employ a consistent procedure because conditioning times can vary widely and potentially risk exposing vaccines to freezing temperatures. Annex 3 of WHO IVB 15.03 can offer further information regarding the conditioning process.

You should avoid loading extremely warm gel packs into a freezer because they can alter the refrigerated space’s internal temperature, and without additional time to compensate, fail to freeze them completely. It is also critical to realize that freezing times will differ depending on the number of gel packs you place into a freezer. Essentially, the quantity and size of the PCMs that you load will affect freezing times.

Also, avoid snap-freezing vaccines. Snap freezing (aka flash freezing), a process that occurs when samples are reduced to temperatures below minus-70 degrees Celsius achieves the same endpoint as slower controlled freezing. However, some studies have shown that the variability in freezing profiles caused by “user error” or “user technique” contributed to change.

When placing a gel pack into a freezer, you should ensure adequate air circulation around its two large, flat sides. This placement method is key because it allows a freezer’s airflow to maximize its exposure to the gel pack, increase the conditioning effects’ consistency, and decreases the risk of product damage. Furthermore, avoid snap freezing and prevent excessive airflow from reaching a gel pack’s smaller sides when it’s not on its large, flat face.

A gel pack’s contents will enlarge during the freezing process as it morphs from a liquid into a solid. When this modification happens, a frozen gel pack can become distorted, and its outer barriers can become brittle. Hence, you’ll want to handle a fragile PCM with great care when transporting it from a freezer to a container. It’s also crucial to understand that a damaged gel pack will remain undetectable after the freezing period until it begins to liquefy.

Frozen gel packs directly removed from the freezer are not suitable for immediate use. Once fully frozen, the gel pack(s) should be removed from the freezer and left at room temperature on its two large, flat sides until its ice starts to melt and liquid begins to develop. Although multiple factors, including light, gel pack mass, humidity, and air temperature, can change the time it takes to condition a gel pack, this phase change typically takes around 30 minutes when left at room temperature.

It is critical to remember that this is the approximate amount of time needed to condition a gel pack and not how long it takes to freeze it, which can take 24 hours or longer. Also, a lower starting temperature can exaggerate the effects of thermal shock. Once conditioned, you can immediately utilize them in a pre-qualified shipping container or climate-controlled vehicle.

The World Health Organization (WHO) reports a gel pack suitably conditioned once it stabilizes at 0 degrees Celsius. A correctly conditioned gel pack has melted enough that ice can move inside the pack. Similarly, you may notice moisture or “sweating” on the gel pack’s exterior.

Conditioning Gel Packs for Larger Applications

For bulk shipping, such as those shipped in a crate or palleted, you will typically receive your refrigerants as a full pallet, with several cases loaded onto it. You will condition your full pallets as they are received.

As mentioned earlier, mass, air circulation, pallet stacking, and more can influence the number of days required for an entire pallet of refrigerants to stabilize. The larger the mass and weight, the longer you should plan for conditioning time. The refrigerants bordering the outside of the container will stabilize their temperature faster than those in the pallet center. This is because the colder area “touches” the outside of the pallet before it does the inside. Depending on the freezer or refrigerator, it would be best if you planned anywhere from one to two weeks for a fully loaded pallet of refrigerants to refrigerate or freeze.

Refrigerated Gel Packs

As a manufacturer of vaccines or pharmaceutical products, you already recognize a unique set of guidelines for refrigerating a gel pack rather than freezing it. Initially, ensure a refrigerator’s airflow is fully functioning and large enough to cool all the loaded PCMs to a temperature between 5 degrees Celsius and minus-1 degree Celsius within the given timeframe.

Like when freezing a PCM, avoid loading excessively warm gel packs into a refrigerator as it can modify its temperature and hinder the cooling process. It’s also important to know that refrigeration times will differ depending on the number and size of the gel packs you place in a cooling space. A simple way to remember this is to consider total gel pack mass instead of the number of gel packs loaded.

Lastly, don’t place PCMs in a refrigerated area susceptible to colder temperatures than you want to maintain and avoid stacking an unnecessary amount of them because they will cool slower as a unit. An electronic temperature indicator or recorder should be used to ensure protection and tracking.

Once gel packs are properly refrigerated and conditioned, use them immediately upon being removed from the cooling space.

Guidelines and Support

The process of transporting pharmaceuticals along the cold chain is strictly regulated. Therefore, to comply with domestic and international pharmaceutical shipping standards and regulations, adhere to the five basic rules below:

  1. Ship and store all products at the required temperature using properly qualified and validated shipping containers, vehicles, and facilities.
  2. Monitor the temperature throughout the shipping and handling process.
  3. Manually and carefully inspect all products for any signs of potential damage.
  4. If the product’s quality is potentially compromised, destroy it or return it to the supplier for further investigation.
  5. Maintain electronic records to validate that the product’s temperature has remained constant throughout the entire process.

If you need help achieving your cold chain objectives and goals, contact the team at TempAid.



How frozen is frozen;

Study of separation distance during ice-pack conditioning – Path 

World Health Organization –

How Frozen is Frozen? – Contract Pharma –

6.2.3 Ice-packs – The Open University

This article is for reference only. Readers should follow the guidelines outlined by the appropriate standards organization and internal documentation.