Stability testing is a key aspect of testing the shelf life of pharmaceutical drugs. Two main types of stability programs are used in this industry, accelerated stability, ASAP, and long term stability.
Accelerated stability gives a general idea of how the product will perform over time. This enables scientists to determine how long the active pharmaceutical ingredient, API, is viable for entry into the body. After a certain point the drug will expire, either by changing into another polymorph or by degrading into entities that are not able to be absorbed by the body or are not therapeutically effect when introduced into the body. This particular study determines the shelf life, or expiration of a drug.
It is important to keep in mind that ASAP testing gives a general idea to predict the shelf life of the drug, but only the true long term data proves exactly how the drug reacts and the length of the shelf life. The reason ASAP is not truly representative of how the drug will perform is because it is put at extreme conditions to accelerate degradation and get a model to determine the potential outcome of the viability of the drug. The accelerated stability program provides insight without having to wait a true 3 or 4 years. That information still must also be collected, but if any extreme red flags are raised with the accelerated stability results these can be addressed sooner than later. This aids in hastening the overall time it takes for a developed product to get to market.
Accelerated testing of pharmaceuticals is done by placing the dosage at various temperatures and relative humidities to see how the drug reacts. Generally this will induce degradation as well as impurities. The dosage is placed at the various conditions for specified time periods, usually a day, a week, two weeks, three weeks, four weeks, and then pulled monthly for a few months. These time frames for the duration the samples are in the chamber also depend on the specific condition. Higher temperatures and relative humidities will have the samples in the chamber for less time than samples at a lower temperature and humidity. This is just a general idea of a generic accelerated stability protocol setup.
Once the samples have completed their duration in the stability chamber the samples are assayed via high pressure liquid chromatography, HPLC, to determine the percentage of drug in the dosage as well as the percentage of degradation and the amount of impurities present within the sample. This gives a general idea of the overall stability of the drug.
Some stability testing companies like Particle Sciences, Inc. follow ICH Guidelines.