Blending means combining material within the same specification to make a homogeneous intermediate or API; mixing fractions within a batch or combining fractions for further processing is part of production, not blending. A batch that fails specification should never be blended with others to bring it into specification; every batch in a blend should have been made by an established process and individually tested and found within specification. Acceptable blending includes combining small batches to increase batch size and combining tailings of the same product into one batch. Blending should be controlled and documented, the blend tested where appropriate, and the batch record should trace back to each component batch. Where physical attributes are critical (for example APIs for solid oral forms or suspensions), blending should be validated for homogeneity including attributes such as particle size distribution, bulk and tap density. If blending could affect stability, blended batches should be stability tested, and the blend's expiry or retest date based on the oldest tailings or batch in it.
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