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The comparative bioavailability of a drug in similarly formulated preparations is becoming a subject of considerable interest and importance to the physician. Drugs usually are not administered as pure compounds but are combined with materials such as binders, excipients, lubricants, preservatives, or other substances generally considered to be pharmacologically inert. The resultant blend, granulation, or pill mass is packed into capsules, compressed into tablets, or manipulated into any one of many other physical forms. Until recently, the pharmacopeias that specify and describe the standards for preparations of drugs have been constructed largely on the premise that only the quantity and quality of the active drug determines the efficacy of the final preparation. This tenet is no longer valid. Currently, an overwhelming body of evidence is accumulating that indicates that the manner in which a composite medication is produced from its component parts can exert a major influence on the rate
Schiffman DO. On Therapeutic Equivalency and the Antisubstitution Laws. JAMA. 1973;223(5):552-553. doi:10.1001/jama.1973.03220050052014