Simulating long-term storage of a product by using extreme conditions is a common practice in many industries. It is particularly important in the pharmaceutical industry for determining expiration dating of drug products. This is usually called stability testing.

Because of the tremendous cost in time and money required to develop a new drug, it is important to get it to market as quickly as possible so that these expenses can be recovered while the product is still protected by a patent. As a result, regulatory agencies such as the FDA have developed guidelines for doing accelerated testing so that a drug can be approved for sale without real time data confirming the expiration date. This can prevent huge delays if you happen to have a product with a five year shelf life.

A stability study on a pharmaceutical product essentially involves repeating quality control testing at regular intervals and using statistical analysis of the data to determine the longest acceptable shelf life that will ensure the safety of the product. Things that can affect the shelf life include:

A real time stability study involves samples stored at the conditions specified on the label (eg. Store at room temperature protected from light.) for the entire shelf life or longer. Accelerated studies are started at the same time. A room temperature (approx. 25oC) product with a three year shelf life might have studies at 30oC and 40oC for shorter periods of time. A product that is intended to be stored in a freezer would generally be tested after a period of days refrigerated and/or at room temperature. Solutions in semi-permeable plastic bags might be tested at low humidity to see how quickly the drug concentrates as water is lost (sometimes drug degradation can offset this concentration effect). Photostability studies are also performed in which the product is exposed to tremendous amounts of ultraviolet and visible light to see if the drug degrades. In some cases the FDA will approve a product with a shelf life of a couple of years based on as little as three months of accelerated testing. The drug company then sends regular updates to the FDA as the real time study progresses to show that the product will be safe at the intended expiration date.