Basics of compounding: potency and stability testing.

Potency (strength) tests are designed to determine how much of an active drug is in a sample. Stability tests are used to determine an expiration date of a product or a beyond-use date of a preparation. Being able to employ the proper method to determine potency or stability is the key to understanding the difference between potency testing versus stability testing. In order to determine potency, a method may or may not be stability indicating. When determining stability, the method must be stability indicating. When using a stability-indicating method, both potency and stability can be determined. 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-assurance program.