Blending validation and content uniformity of low-content, noncohesive powder blends

Blending validation has become mandatory, partly through good manufacturing practice (GMP), partly through a court action (the Barr decision) in 1993. Although feasibly carried out with existing technology, there are situations where the methodology for sampling causes a suspected bias in the figures, and one such care is where the drug content (expressed as fraction x in the following) is low. In particular, this dilemma is predominant where the blended materials are not cohesive. Possible explanations for this are voiced, as are suggestions on how to proceed rationally in such cases.