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Glossary of Pharmacology 



In pharmacology, this term refers to the process of biotransformation, usually by enzymes, where one chemical species is converted to another. A parent compound is metabolized to a metabolite. The metabolite is the by-product of the reaction and may be less, more, or equal in activity (therapeutic or adverse) to the parent compound. 


Although a goal of metabolism is to render water-soluble metabolites for elimination, through metabolism, the body can convert an inactive compound (prodrug) into its active form that possesses therapeutic actions. Similarly, the body can terminate a drug's activity via metabolism. It is essential to mention that not all drugs are metabolized; a drug may exert its actions and then be eliminated without undergoing metabolism.  

While the liver is the primary site of drug metabolism, other organs such as the small intestine, lungs, kidney, brain and nasal mucosa have drug-metabolizing capacity. The rate at which drug metabolism occurs is affected by several factors, including diet, presence of inflammatory mediators, degree of protein binding, ontogeny, physiological changes associated with ageing and genetic factors. Concerning the genetic variability of metabolizing enzymes, individuals can vary from being poor to ultrafast drug metabolizers.  

Teaching tips:  

The concept of metabolism can be used to teach 

  • Drug-drug and drug-food interaction 
  • Individual variability to drug response 
  • Age-related variability to drug metabolism 
  • The effects of gender, race and/or ethnicity in drug metabolism  
  • The impact of diseases in drug metabolism  
  • The impact of genetic background on metabolism 

Linked terms: biotransformation, bioavailability, pharmacogenetics 

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