Unit dose sampling
Unit dose sampling (UDS) is a sampling method used in pharmaceutical production to verify and ensure "content uniformity". Content uniformity refers to the homogeneous distribution of the active ingredients within the mixture of excipients, fillers and active ingredients. The test method, which is also called Blend Uniformity Analysis (BUA), is described in more detail in the FDA and GMP guidelines.
Since this method has to prove that content uniformity is also given for the smallest applicable dose, as a rule only one to three times the amount of this dose may be taken as a sample and subjected to a Blend Uniformity Analysis. Taking such small and at the same time representative samples is enormously difficult, as the insertion and movement of instruments and samplers can already lead to segregation. The different parts of a mixture can have different adhesion and flow properties and this can lead to the sample no longer being representative due to the intervention. Electrostatic effects can also complicate sampling.