TBD Excretion

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					     Pharmacokinetics (PK)
The study of the disposition of a drug
The disposition of a drug includes the
 processes of ADME -
     Absorption
     Distribution
     Metabolism
     Excretion      Elimination
ADME
            Importance
Without the knowledge gained from PK
 studies, patients may suffer:
   Toxic drugs may accumulate
   Useful drugs may have no benefit because
    doses are too small to establish therapy
   A drug can be rapidly metabolized.
       Routes Of Administration
                        Routes Of Drug
                        Administration


            Parenteral                     Enteral

Injection     Topical    Respiratory   Rectal        Oral
           Absorption
The passage of drug from the site of
 administration into the general
 circulation.
Exception: Intravenous injections
      I.V Drug        Oral Drug
      Immediately     Delayed
     completely     incomplete
              The Process

Absorption relies on
   Passage through membranes to reach the
    blood
   passive diffusion of lipid soluble species.
Absorption & Ionization

      Non-ionised drug


    More lipid soluble drug


      Diffuse across cell
    membranes more easily
          Site Of Absorption

Most drugs are absorbed in the small
 intestine, because
   It is the portal for absorption of nutrients into
    blood
   It is surrounded by a very thin
    membrane with a large surface
   area
           Rate & Extent

Rate - How rapidly does the drug get
 from its site of administration, to the
 general circulation?
Extent - How much of the
 administered dose enters the general
 circulation
          Distribution
The movement of drug from the blood
 to and from the tissues
      Plasma Protein Binding

Many drugs bind to plasma proteins in the
 blood steam
Plasma protein binding limits distribution.
A drug that binds plasma protein diffuses
 less efficiently, than a drug that doesn’t.
           Elimination
The irreversible removal of the parent
 drugs from the body

                Elimination


    Excretion            Drug Metabolism
                        (Biotransformation)
         Drug Metabolism
The chemical modification of drugs with
 the overall goal of getting rid of the drug
Enzymes are typically involved in
 metabolism
         Metabolism     More polar      Excretion
  Drug
                      (water soluble)
                           Drug
     Sites of Drug Metabolism

Metabolism occurs in many tissues
E.g. brain, kidney, lung
But mostly in the liver because …
 all of the blood in the body passes
 through the liver.
          Intravenous
         Administration

                                     Oral
                                  Administration




Metabolism                Liver




                                       Intestines
  Consequences Of Metabolism

Drug metabolism != Drug inactivation
The metabolite may have
     Equal activity to the drug
     No or reduced activity
     Increased activity (Prodrugs)
     Toxic properties, not seen with the parent
      drug
  The Most Important Enzymes

Microsomal cytochrome P450
  monooxygenase family of enzymes,
  which oxidize drugs
Act on structurally unrelated drugs
Metabolize the widest range of
drugs.
             Excretion
The main process that body eliminates
 "unwanted" substances.
Most common route - biliary or renal
Other routes - lung (through exhalation),
 skin (through perspiration) etc.
Lipophylic drugs may require several
 metabolism steps before they are
 excreted
ADME - Summary
   Pharmacodynamics (PD)
The study of the biochemical and physiological
 effects of drugs.

   Pharmacokinetics Pharmacodynamics


   what the body does   what the drug does to
   to the drug          the body.
         Drug Interaction
When a drug alters the effects of another
 drug
Drug A may alter these factors of drug B:
   Efficiency
   Rate of effect
   Side effects.
                 Drug Interaction


Pharmacodynamic:             Pharmacokinetic:
The drug effect is altered   Amount of drug in blood
                             is altered
                    References
 A First Course in Pharmacokinetics and Biopharmaceutics - available
  at http://www.boomer.org/c/p1/
 http://www.le.ac.uk/pa/msc/pklecture.pdf
 http://web.vet.cornell.edu/public/pharmacokinetics/pharmacokinetic
  s.html
 The Liver and Drug Metabolism - available at
  http://adultpain.nursing.uiowa.edu/MedGen/Liver.htm
 http://www.ttuhsc.edu/pharm/Freeman/med/DrugElim1.ppt
 http://www.bps.ac.uk/epharnet/adme.ppt
 http://www.usask.ca/medicine/pharmacology/Mon11SEP.pdf
 http://www.usask.ca/medicine/pharmacology/Fri08SEP.pdf

				
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posted:4/21/2011
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