What a Shelf-Life Study Tells You

Shelf life is the period during which a packaged product stays safe, stable and acceptable under stated storage conditions. The date printed on the pack is a promise, and a shelf-life study is the evidence behind it.

One principle shapes every study: shelf life is never a property of the product alone. It depends on the product, the packaging around it and the conditions it is stored and transported in. Change any one of the three and the answer can change.

Real-Time Studies

In a real-time study the packaged product is stored at the conditions it will meet in normal storage and sale, and samples are taken at planned intervals across its full intended life. At each interval the product is checked against agreed limits, which might cover moisture content, texture, taste, colour, microbial counts or, for medicines, the assay and degradation products.

Real-time data is the most direct evidence there is. Its drawback is obvious: a two-year shelf life takes two years to confirm.

Accelerated Studies

An accelerated study stores the product at raised temperature, and often raised humidity, so that the changes that limit its life happen faster. The results are then used to estimate the shelf life at normal conditions.

Accelerated testing is valuable for comparing packaging options quickly and for supporting a provisional shelf life while real-time data builds up. It has limits that a careful study plan takes into account:

• Not every change speeds up in the same way with temperature. Fats can melt or separate, and some reactions only appear at high temperature, so the product can fail at test conditions in a way it never would on a shelf.
• The packaging itself behaves differently. Films let through more moisture and oxygen at higher temperature and humidity, so the barrier under test is not the barrier in the market.
• An estimate is only as good as the model behind it, and the model should be confirmed by real-time results.

Pharmaceutical Products

For medicines, stability testing follows the ICH guideline Q1A(R2), which sets out long-term and accelerated storage conditions. The accelerated condition is 40°C and 75% relative humidity for six months. Long-term conditions depend on the climatic zone of the market; products for India are generally studied at the hot and very humid Zone IVb condition of 30°C and 75% relative humidity. The packaging used in the study must be the packaging the product will be sold in.

The Part the Packaging Plays

Packaging protects a product from moisture, oxygen, light, contamination and physical damage. Three groups of tests measure how well it does that job:

• Water vapour transmission rate (WVTR) shows how much moisture passes through a film, laminate or container.
• Oxygen transmission rate (OTR) does the same for oxygen, which drives rancidity, colour change and the loss of some active ingredients.
• Seal strength and leakage tests check that the pack is closed as well as its material is good. A strong barrier film with a weak seal is a weak pack.

These tests are also the quickest way to judge a packaging change. If a supplier offers a thinner film, a different laminate or a new blister foil, comparing WVTR, OTR and seal performance tells you whether the existing shelf-life data still applies or whether the study needs to be repeated.

A Claim You Can Defend

When a customer, an auditor or a regulator asks how you arrived at the date on the pack, a good answer names:

• the storage conditions used, and why they represent the market;
• the exact packaging tested: material, structure, closure and pack size;
• the properties checked at each interval, and the limits that define the end of shelf life;
• which part of the claim rests on accelerated data, and how and when it is being confirmed in real time.

Planning a study starts with three facts: the product, the packaging and where it will be sold. From those, the right combination of real-time, accelerated and packaging performance tests can be chosen.