MDI and DPI Drug Products
...establish a set of criteria to which a drug substance or drug product should conform using.....An alternative approach may be used if such approach satisfies the requirements of the.....formulation, moisture level, consistency of filling operation, particle size distribution..
http://www.fda.gov/cder/guidance/2180dft.pdf (score=100)

Substance
...individual batches of the drug substance used in animal and clinical testing, Drug Substance.....less than 5 milligrams per milliliter) both the typical original particle size distribution and the particle size.....Production of a drug substance, whether by synthesis, fermentation, or isolation, usually..
http://www.fda.gov/cder/guidance/drugsub.pdf (score=79)

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