Term
| what is the Volume of Distribution equal to? |
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Definition
| the (apparent) volume of fluid that would be required to contain the total amount of drug in the body at the same concentration as in plasma |
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Term
| what does it mean when it says Vd is CONSTANT? |
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Definition
| NOT dependent on administered dose |
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Term
| how is the VOLUME OF DISTRIBUTION measurement used? |
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Definition
-To get a rough indication of the overall distribution of a drug in the body
-To plan dosage regimens
-To achieve a rough indication of the efficacy (or toxicity) of a given dose of a drug |
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Term
| what do drugs mainly BIND to? two most common examples? |
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Definition
| plasma protein -->ALBUMIN (if acidic) or to ALPHA1-ACID-GLYCOPROTEIN (if basic) |
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Term
| is the extent to which drugs are bound to protein VARIABLE or CONSTANT? |
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Definition
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Term
| PROTEINS that are bound are not available for what actions? |
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Definition
a) pharmacological actions
b) further distribution throughout the body
c) biotransformation
d) glomerular filtration |
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Term
| how do Drugs reach the CNS? |
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Definition
a) CROSS THE CEREBRAL CAPILLARIES (i.e from plasma to the interstitial fluid)
b) CROSS THE CHOROID PLEXUS (i.e from plasma to the cerebrospinal fluid) |
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Term
| The blood-brain barrier limits the transfer of drug into the central nervous system because: |
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Definition
-BRAIN CAPILLARY CELLS and CHOROID PLEXUS CELLS are bound together by an OCCLUDING ZONULAE
-Several drugs are actively transported out of the cerebrospinal fluid and back into the blood by a P-glycoprotein |
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Term
| TRANSFER OF DRUGS ACROSS THE BLOOD-BRAIN BARRIER CARRIES WHAT REQUIREMENT? |
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Definition
| must be LIPID soluble (lipid diffusion used) |
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Term
| if a drug is not LIPID SOLUBLE, what method must be used to breach blood brain barrier? |
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Definition
| must be administered by INTRATHECAL INJECTION directly into the CSF |
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Term
| when is the BBB PERMEABILITY increased? |
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Definition
| INFANTS and NEWBORNS, sickness (meningitis) |
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Term
| is the PLACENTA typically permeable or impermeable to most drugs? is equilibration between mother and fetus generally fast or slow? |
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Definition
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Term
| Factors affecting placental transfer of drugs include: |
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Definition
-drug size
-physicochemical properties of the drug (lipophilic +)
-degree of protein binding (drugs highly protein bound cross the placenta slowly)
-placental blood flow
-stage of placental development (later=better)
-placental drug metabolism
-activity of the of P-glycoprotein that is present in placental vessels |
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