Stability Versus Potency Testing: The Madness is in the Method.

Potency tests, known as quantitative tests, are designed to determine how much of the active drug is in the sample. Stability tests are used to determine a beyond-use date for a preparation. Employing the proper method to determine potency or stability is key to understanding the difference between potency testing and stability testing. Methods of determining potency may or may not be stability-indicating, but stability can be determined only by a stability-indicating method. A stability-indicating method can determine both potency and stability. Quality assurance programs are essential to establishing standards for compounded preparations. It is important that compounding pharmacists understand the differences between potency and stability tests and that these tests are made an integral part of the quality asurance program.