Second lec& 3rd
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Second lec& 3rd

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  • جزاك الله كل الخير على سلسلة محاضرات الكيمياء الطبية

    هنل هناك كتاب باللغة العربية للكيمياء الطبية ؟

    هل هذه الساليدات لجامعة سعودية ؟



    سبحان الله وبحمده سبحان الله العظيم
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Second lec& 3rd Second lec& 3rd Presentation Transcript

  •  
    • Physicochemical Properties of Drugs
    • The Effect of pH and pKa on Drug Action
    • most drugs are small organic molecules that
    • behave in solution as either weak acids or weak bases.
    • Acid-Base properties of drugs greatly influences their biodistribution and partitioning characteristics.
    • What does it mean to say that a certain molecule is an acid or base?
    • Arrhenius definition.
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  • and Base Strength ِ Acid ِ
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  • Percentage Ionization
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  • Example
    • What is the ratio of ephidrine to ephedrine HCl (pKa 9.6) in the intestinal tract at pH 8.0?
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    • What is the percentage ionization of: 1. ephedrine HCl (pKa 9.6) and 2. indomethacin (pKa 4.5) in an intestinal tract with pH 8?
    • pKa for the base is the pKa of its conjugate acid.
    • Ephedrine pKa =9.6
    • Ammonia pKa=9.3
    • What is the significance of Ka and pKa values?
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    • How can the drug pKa value be used?
  • Rules Acid drugs – become more NON ionized in acidic pH Basic drugs – become more NON ionized in basic pH (alkaline pH) Acid Drug Basic Drug Acid pH Environment Basic pH Environment
  • Rules Acid drugs – become more NON ionized in acidic pH Basic drugs – become more NON ionized in basic pH (alkaline pH) Acid Drug Basic Drug Acid pH Environment Basic pH Environment NON-ionized NON-ionized
  • Rules Acid drugs – become more NON ionized in acidic pH Basic drugs – become more NON ionized in basic pH (alkaline pH) Acid Drug Basic Drug Acid pH Environment Basic pH Environment NON-ionized NON-ionized IONIZED
  • Rules Acid drugs – become more NON ionized in acidic pH Basic drugs – become more NON ionized in basic pH (alkaline pH) Acid Drug Basic Drug Acid pH Environment Basic pH Environment NON-ionized NON-ionized IONIZED IONIZED
  • Rules Hydrophilic = Ionized molecules (charged) Lipophilic = Non-ionized molecules (non charged) Lipophilic molecules penetrate membranes Hydrophilic molecules dissolve in water
  • Depending if a molecule is ionized or not determines if it can pass through a cell membrane C E L L M E M B R A N E Ionized Molecule Non-Ionized Molecule
  • Need three things to figure out whether drug is MAJORITY in lipophilic or hydrophilic form
    • Whether the drug is an acid drug or a base drug.
    • The pKa of the drug (pH at which number of ionized = number of nonionized molecules)
    • pH into which the drug is going to be placed
  • Acid Drug = Non ionized molecules = Ionized molecules Acid drugs – become more NON ionized in acidic pH pH 2 N I pH 6 N I pH 9 I pH 8 I N
  • Basic Drug = Non ionized molecules = Ionized molecules Basic drugs – become more NON ionized in basic pH pH 9 N I pH 8 N I pH 2 I pH 6 I N
  • WHEN GIVEN:
    • Acid / Base nature of the drug
    • Drug’s pKa
    • Environmental pH drug is put into
    • Be able to predict whether majority of drug is in the ionized form or non-ionized form
    • Be able to state whether majority of drug is in the hydrophilic form or lipophilic form
    • Be able to predict whether it can be absorbed across membrane or dissolved in water
    • Examples
  • Carboxylic Acids
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  • Phenols
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    • The End