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15 Cards in this Set

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define drug distribution
process by which a drug reversibly leaves the bloodstream and enters the interstitium (ECF) and/or the cells of the tissues
in order to deliver the drug from plasma to the interstitium, what type of delivery is needed?
1. blood flow
2. capillary permeability
determined by capillary structure, and drug structure (hydrophobic)
3. degree of binding of the drug to plasma and tissue proteins - binding relatively nonselective as to chemical nature (plasma albumin)
4. relative hydrophobicity of the drug
define volume of distribution
a hypothetical volume of fluid itno which a drug is disseminated. Vd relates a concentration of drug measured in the blood to the total amount of drug in the body
what are the relative size of various distribution volumes in a 70kg individual
total body water (plasma, interstitial volume, intracellular volume) 42 L
-intracellular vol 28 L
-extracellular volume 14 L
-interstitial vol 10 L
-plasma vol 4 L
what type of curve would describe drug concentrations in serum (w/out elimination) after rapid injection of drug? then with elimination?
1.5 rapid drop to 1, and then steady. drop phase is the distribution phase. with elimination, the curve would continue downward, and would be called the elimination phase
explain the distribution of drug in water compartments in the body for
1. drug hi MW
2. drug lo MW, hydrophilic
3. drug lo MW, hydrophobic
4. during pregnancy
1. plasma compartment will bind to plasma proteins - distributes to vol of plasma 6% body weight, abotu 4L (ex. heparin).
2. can move through endothelial slits at capillary junctions. distribute to plasma water and interstitial lfuid, 20% body weight, or 14 L (ex. aminoglycoside antibiotics)
3. can move through interstitium at slit junctions, moves into intracellular fluid. volume 60% of body weight, or 42L (ex. ethanol)
4. fetus may tay up and inc Vd (ex. thiopental)
how do you determine Vd in the absence of elimination?
Vd (Litres) = total amount of drug in the body(D) / plasma concentration of the drug (C)
explain elimination process
when drug distributed through body, it will leave the body fluids by renal or biliary excretion oy by hepatic biotransformation. rate at which drug is eliminated is usu proportional to the conc of the drug. that is the rate for most drugs is first order and shows linear relationship with time if ln C is plotted versus time
calculation for desired plasma concentration
difference btw 2 values is the additional dosage needed Vd(C2-C1). where VdC1 is amount of drug initially in the body. VdC2 is amount of drug in the body needed to achieve the desired plasma conc. where C1 conc drug in plasma, & C2 is desired drug plasma level
what is the difference in drugs when bound/unbound to plasma proteins? char of most common plasma protein?
when bound (usu. albumin) drugs are pharmacologically inactive. when free unbound drug can: act on target sites in the issues, elicit a biological response, be available to the processes of elimination.
hypoalbuminemia may alter level of free drug. with albumin, binding capacity is reversible, low capacity if 1 drug molec/albumin. high capacity if # drug molec/1 albumin molec. affinity - strongest for anionic drugs (weak acids) and hydrophobic drugs. most hydrophilic drugs and neutral drugs do not bind to albumin.
what are the 2 classes of high affinity drugs which compete for albumin? what happens when administered simultaneously?
1. class I drugs - dose is still less than available binding sites. most drug molecules are bound to albumin, and the concentration of free drug is low.
2. class II drugs - dose is greater than the available binding sites. most albumin molec contain a bound drug, and the conc of free drug is significant. administration of both simultaneously results in displacement of class I drugs with class II drugs.
what controls the displacement of drugs from albumin?
drug displacement from albumin depends on both Vd and therapeutic index of drug.
what is the relationship of a large Vd to drug displacement, half-life, and duration of drug action?
If Vd is large, the drug displaced from the albumin ends up in the periphery, so free drug conc in plasma is not sig changed. Any factor that that inc the Vd can lead to an inc in the half-life and extend the duration of action of the drug.
what is the relationship of drug displacement to Vd?
if the Vd is small, the newly displaced drug does not move into tissues as much, and the inc in free drug in the plasma is more profound.
what is the relationship of drug displacement with the therapeutic index?
If the TI of drug is small, the inc in drug conc may have sig clinical consequences.