Pharmacokinetics. What is biotransformation?

The following pharmacological definition has been taken from the Pharmacology and Experimental Therapeutics Department Glossary at Boston University School of Medicine .


Chemical alteration of an agent (drug) that occurs by virtue of the sojourn of the agent in a biological system. Spontaneous decay of radium would not be considered a biotransformation even if it occurred within the body; chemical alteration of a chemical by enzymatic attack would be considered a biotransformation even if it occurred in a model system, in vitro. Pharmacodynamics involves the chemical effects of a drug on the body; biotransformation involves the chemical effect of the body on a drug! “Biotransformation ” should be used in preference to “drug metabolism”, and the word “metabolism” should probably be reserved to denote the biotransformation of materials essential to an adequate nutritional state. “Biotransformation” and “detoxication” are not synonyms: the product of a biotransformation may be more, not less, biologically active, or potent, than the starting material.

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

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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