movement of drug molecules from their site of application into the bloodstream
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For a drug to be absorbed it MUST be
Dissolved in solution
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Ideally what form if the drug is best for absorption
unionised form/uncharged
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Distribution
the movement of drug molecules between the blood and the tissues of the body
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Volume of distribution
measures the tendency of drugs to remain in the blood - V=D/C
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Small VoD
tendency of drug to remain in the blood
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large VoD
tendency of drug to move into the tissues
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Metabolism
enzymatic conversion of one chemical compound into another
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Where does most drug metabolism occur?
Liver
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Main purpose of metabolism?
to convert drug into more active form/ more polar so it will stay dissolved in water and therefore be excreted
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Phase 1 Metabolism
Redox reactions, hydrolysis, OH groups added- make more polar and hence more water sol
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Phase 2 metabolsim
conjugate reactions- molecule from p1 or the drug molecule is joined to conjugate molecules i.e AAs - to increase size and polarity
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Drugs under go which phases of metabolism
some just P1, some just P2, some both and some neither
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If drug undergoes neither P1/2
the drug is excreted chemically unchanged in the urine
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Excretion
the physical removal of drugs from the body- skin,lungs,urine, etc
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Bioavailablity
The proportion of an administered dose, which is absorbed chemically unchanged that reaches systemic circulation
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oral bioavailability
proportion of oral dose which reaches systemic circulation
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why is bioavailability not 100%?
1st pass met. enzymatic/chemical attack. Failure to absorb. Failure of dissolution
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1st Pass met
when a drug is metabolism before it ever reaches systemic circulation
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pgp
p- glycol proteins
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what do pgp do?
pgp can inhibit absorption of lipid sol drugs that would normally be freely absorbed by the p.membrane. they do this by expelling the drug into the gut.
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