Pharmacokinetics topics. What is a generic drug?

This generic drugs definition has been taken from the Pharmacology and Experimental Therapeutics Department Glossary at Boston University School of Medicine .

Generic Drugs:

Drug formulations of identical composition with respect to the active ingredient, i.e., drugs that meet current official standards of identity, purity, and quality of active ingredient. Drug dosage forms considered as “generically equivalent” are more properly considered as “chemically equivalent” in that they contain a designated quantity of drug chemical in specified stable condition and meet pharmacopoeial requirements for chemical and physical properties.

Each of a number of preparations of a given drug entity may carry a different “proprietaryname” or “trademark”; such a name is registered with the U.S. Patent Office and identifies the special brand of the drug with the firm owning the name. All such preparations – identical with respect to content and specification of active ingredient – may be looked upon as comprising a “genus”; they are generically equivalent and are generic drugs. FDA regulations require manufacturers of generic drugs to establish biological equivalence of their product to the original patented drug product.

It is well recognized that a number of factors other than quantity of drug present in a dose can determine the ultimate therapeutic usefulness of the drug preparation, and even the availability of drug to the site of action once the preparation has been given. Drugs may be generically equivalent but not therapeutically equivalent. Factors which affect therapeutic usefulness or efficacy of drug preparations include appearance, taste, disintegration and dissolution properties of the preparation, interaction of active materials with other ingredients including binders and solvents, pH, particle size, age of preparation, conditions of manufacture such as degree of tablet compression, and the nature and amount of coating of enteric-coated tablets.

When the patent of a proprietary drug expires, a manufacturer must establish the biological equivalence of its generic formulation in order to market the product. To do so, the bioavailability if the generic formulation is compared to the proprietary product in a cross-over experiment.

The copyright of the text is held by Trustees of Boston University. Permission has been granted for its use in this blog.

The FDA created this PowerPoint presentation explaining important concepts to understand what generic drugs are.

Download PDF: What you want to know about generic drugs

Recommended pharmacokinetics reading

  • Pocket Guide: Pharmacokinetics Made Easy (2009)
  • Basic Clinical Pharmacokinetics (2009)
  • Concepts in Clinical Pharmacokinetics (2010)
  • Clinical Pharmacokinetics, 4th Edition (2008)
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