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Drug Metabolism. Where? First-Pass Effect More than 1 metabolite! Varies depending on species, age, gender, genetic variation, disease. Phase I Oxidations Reductions Hydrolysis. Phase II Synthetic/Conjugation. Phases of Drug Metabolism. Phase I Oxidations.

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Drug metabolism
Drug Metabolism

  • Where?

  • First-Pass Effect

  • More than 1 metabolite!

  • Varies depending on species, age, gender, genetic variation, disease


Phases of drug metabolism

Phase I

Oxidations

Reductions

Hydrolysis

Phase II

Synthetic/Conjugation

Phases of Drug Metabolism


Phase i oxidations
Phase I Oxidations

  • Hydroxylations of N, C, S atoms

  • N-, O-, and S- dealkylations

  • Oxidative Deaminations

  • ROH RCHO RCOOH


Phase i oxidations the enzymes
Phase I Oxidations: The Enzymes

  • Mixed Function Oxygenases found in smooth ER, e.g. Cytochrome P-450

  • Microsomal Flavin Monoxygenase (FMO)

  • Alcohol Dehydrogenase

  • Xanthine Oxidase

  • Monoamine Oxidase (mitochondria)


Oxidative deamination dealkylations
Oxidative Deamination/Dealkylations

  • Can occur on N-, O-, S-, or X- systems

  • Begins with hydroxylation, followed by elimination

  • Cytochrome P450 & MAO


Other types of oxidative reactions
Other types of oxidative Reactions

  • ROH  RCHORCOOH

  • RSHRSSR

  • Desulfuration (C=S C=O)


Hydrolysis
Hydrolysis

  • Nonspecific esterases, amidases

  • Amides hydrolyze more slowly than esters

  • May be stereospecific

  • Occurs in cytosol of cells (liver, kidney, intestine) and in plasma



Reductions
Reductions

  • Less common than oxidations

  • Usually specific enzymes, e.g. aldo-keto reductases, nitro reductases

  • C=O  alcohols

  • NO2  NH2

  • N=N  2 NH2



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