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64 Cards in this Set

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Which drugs are more likely to be bound by plasma proteins (acidic, basic or neutral)?
Primarily acid and netural, HOWEVER: some basic drugs can bind to 1) ∂1-acid glycoprotein, which is an acute phase reactant protein AND 2) lipoproteins
T/F binding to plasma proteins is usually specific.
False, while it can be it's usually not.
T/F the t-1/2 of plasma protein binding is long.
false, binding and release is very short
Is binding to plasma proteins is rarely reversible?
No, it is ALWAYS reversible… lasting miliseconds
How do plasma proteins influence the rate of movement of drug across the membrane? (2) what effect does protein binding have on drug (distribution, clearance and half-life)?
(1) concentration gradients are based on only the free drug not bound. (2) distribution=slower… clearance=slower… half-life=longer
What is the exit of drug from the plasma dependent upon? Active transport or concentration gradient.
concentration gradient
At SATURATION, do changes in plasma binding proteins levels alter the amount of FREE drug in the plasma?
no (NOTE free drug is what has the biological effect)
At SATURATION, do changes in plasma binding protein levels alter the amount of TOTAL drug in the plasma?
yes (NOTE changes in the plasma protein level can make you think you need to adjust the dose, but you don't if the concentration of FREE drug is unchanged)
What can cause changes in plasma ∂-glycoprotein levels (which sequester basic drugs)?
age, pregnancy and some disease states.
What is the half-life of a drug related to?
the amount of plasma protein binding
Stop Here
Do you have to adjust the dose of a drug if there is more plasma protein binding?
No, you only change dosage if free drug levels change
What can cause the plasma albumin levels to change?
age, pregnancy and disease, among other things.
Besides absorption, what other two things do plasma proteins influence?
1. Hepatic or other organ extraction of drugs… 2. Solubilizes some drugs for that are often poorly soluble in water
Is active transport effected by the concentration of plasma proteins?
no, since it's not concentration related
a) What offsets the displacement of drugs plasma proteins in terms of drug effect duration? b) What is the danger in displacement of drug from plasma protens
a) displacement increase the amount of free drug, but it also increase the amount of drug available for metabolism and excretion. b) increasing dosage based on lower plasma concentrations… since once the plasma proteins are saturated, the amount of unbound drug will increase disproportionally to the increase in dose.
a) What can decrease albumin? b) What can decrease the amount of ∂1-acid glycoprotein (basic drug binding protein)?
a) many things… b) aging, oral contraceptives, and pregnancy
Which type of drug binding (basic or acid) is decreased by uremia?
acidic drugs, because they are the ones bound to plasma protein and are the ones displaced by the urea
What is the average volume in liters of the following? A) total body water. B) extracellular water. C) whole blood? D) plasma. E. intracellular water.
A) total body water = 42 L (60%)… B) Extracellular water = 14 L (20%)… C) Whole Blood = 6 L … D) Plasma = 3 L… Intracellular water = 28 L
a) Give the equation for determining the volume of distribution (Vd)… b) when is Vd measured?
a) Vd = Dose ÷ [plasma] (@equilibrium)… b) after a single dose @ equlibrium
What is indicated by Vd = plasma volume?
most of the drug is bound to plasma proteins
What is the clinical importance of knowing the Vd?
its value lies in calculating dose
How do you calculate dose for a IV (100% bioavailability)?
Rearrange Vd equation: dose = Vd X [desired plasma]
How do you calculate dose for drugs with less than 100% bioavailability? (give equation)
Dose = (Vd X [desired plasma]) ÷ F… where F= fraction absorbed into systemic circulation: BA
What can alter Vd?
age, sex, disease, changes in skeltal muscle, fat mass, plasma protein synthesis, fat/muscle ratio, and hydration. etc…
a) What is Total Body Clearance? b) Show equation for determining total Clearance.
a) Total Cl: fluid volume (Vd) cleared per unit time… b) Total Cl = K(elim) X Vd, where K(elim) is the elimination constant
(1) What is the equation for determining half-life?… (2) What is the relationship between t-1/2 and total body clearance (ClT)?… (3) While the Total body clearance Clt can be used to determine how rapidly a drug is eliminated from the whole body, what does it assume?
(1) T1/2= (0.693 X Vd) ÷ Total body Cl… (2) it is inversely proportional… (3) Total body clearance (Clt) assumes the body were one compartment
The change in which organ functions can alter clearance and therby the half-life of a drug? What else can alter the clearance and half-life of a drug?
Kidney, liver, lungs… aging too… can change the clearance and half-life of a drug
What effect does increased clearance have on length of half-life?
increased clearance --> decreased half-life
Which organ is the major factor in non-metabolized drug clearance?… (2) Which organ reflects metabolism?
(1) Non metabolized: kidney… (renal clearance CL-R)… (2) metabolism: Liver (which is due to liver enzymes, as well as, billiary excretion)
How do you calculate hapatic clearance?
hepatic Cl = (drug in bile + metabolite in hepatic venous blood) ÷ [plasma]
How do you determine hepatic clearance in humans?
Cl-hepatic = (drug in bile + metabolite in hepatic venus blood) ÷ plasma concentration… however it can also be calculated like this: Hepatic Cl = Total Cl - renal clearance (Cl-R)
When would a log scale plot of half-life be a straight line?
it would be a straight line when elimination follows first order kinetics and the drug occupies only one compartment
What is the difference between ∂ and ß half-life and which is presumed when discussing half-life?
a) ∂-half-lfe = distribution… ß-half-life is elimination… b) elimination
When would a drug's half-life in the plasma not correlate with the drugs action? (4 reasons)
1. Metabolite is an active form of the drug… 2. Drug activates a nuclear steroid receptor… 3. Drug binds irreversibly to receptor… 4. Drug is an ultra-short acting barbituate
Is elimination half-life route of administration and dose dependent? Why?
not usually, elimination half-life is dervied from a first order rxn, where the plasma concentration does not saturate the rate-limiting step… thus it's calculated after during elimination (ß-t-1/2)and not during distribution
Give the equation for calculating the elimination rate constant k(elim)
K(elim) = 0.693÷ t1/2
Give the equation for t-1/2
t-1/2 =0.693÷K(elim) = 0.693 x Vd ÷ Cl
In which order rxn is the t-1/2 constant? Zero order or first order?
first order, where elimination is not constant
What order rxn is seen when the rate limiting step is saturated? b) Give 3 examples of the above-order metabolized drugs
a) zero order… b) aspirin (when given @ high dose for RA exhibits zero), ethanol (almost always zero order) and phenytoin (plasma disappearance of therapeutic level is zero order… thus it has a narrow therapeutic index and shows difficulty calculating dose.)
What is the time needed to reach the steady state of a drug dependent upon?
half-life (NOT dose, nor dosing rate)
What is the final average steady state dependent upon? Is the plateau effect also dependent on the factors steady state is?
Final average steady state is dependent upon dose and frequency of administration… (2) no, the plateau effect is independent of dose and frequency
What two factors are steady state levels dependent upon?
1. amount of drug absorbed/time and 2. Clearance
What two factors result in smaller fluctuation in plasma concentration?
1. Frequent doses… 2. Slower absorption
What percent of steady state is reached given these numbers of half-lives: 1, 2,3, and 4… what is this called?
1 t1/2= 50%… 2 t1/2= 75%… 3 t1/2= 87.5% … 4 t1/2= 93.75%… this is called the plateau effect
What is the difference between average steady state and plateau steady state?
a) The average steady state takes into account all plasma concentration including fluctuation from initial dose to plateau… b) Plateau is the steady state after multiple doses
As stated earlier, average steady state is dependent upon frequency of dose and absorption, what is plateau steady state dependent upon?
Half-life: For final average steady state: Total input and output... such that input = output at steady state, where the quantity cleared is equal to one dose
After drug withdraw, what is percentage of plasma level are reduced by the following half-lives? 1, 2, 3, and 4
same as above, except reduced: 1 t1/2= 50%… 2 t1/2= 75%… 3 t1/2= 87.5% … 4 t1/2= 93.75%
Give the equation for calculating a single does
Single dose = (Vd x desired plasma concentration) ÷ Bioavailability
Which is the following an example of, dose of dosage (dosing rate)? 3 mg tid
Dosage, where in this example dosage = 25 mg… tid is the dosing interval… (Note: Dose is an absolute quantity, in contrast to dosage, which is a quantity per unit time)
How do you calculate the dose, given the dosing rate?
dose = dosage (or dosing rate) X dosing interval
At steady state plateau, what is dosage equal to?
Dosage is the replacement of cleared drug… in = out
Show the equation for calculating maintenance dosage.
Dosage = (Clearance X plasma concentration) ÷ Bioavailability (fraction absorbed)
Show the equation used for calculating loading dose.
Loding dose = (Vd x desired plasma concentration) ÷ Bioavailability (fraction aborbed)
When would you want to use a modified loading dose?
When the time it take for steady state plateau is long, e.g., 14 hours and wating for 4 half lives to occur would take too long
which type of kinetics for a drug make dosing difficult? (zero or first order)… Why?
zero order are difficult to dose, because in zero order kinetics small changes in dose can cause a large change in plasma levels, whereas in first order kinetics when you double the dose you double the plasma levels
Why is it important to adjust dose for an obese person?
you have to consider whether or not the drug is lipophilic, for example, the drug does not enter fat then a large dose based on weight will lead to an overdose… thus for a drug with a low therapeutic index a small error could be serious.
When should one use a different Vd to calculate dose for an obese person? In these cases, what should one use to recalculate Vd?
when drugs do not enter body fat… (2) Ideal body weight (IBW)
When is body surface area an important consideration?
When the total body surface are is elevated relative to IBW, such as in the obese patient. In these cases you need to increase the dose.
When calculating dose for an obese person, what weight do you use? How do you find this weight for men and women?
Ideal body weight: IBW for men = 52 kg +1.9 x inches in height above 5')… IBW for women = 49 kg + 1.7 kg x (inches above 5')
Do you have to adjust loading dose of a drug for a person with impaired renal function?
No, Loading dose = (Vd x desired plasma conc.) ÷ F (Bioavailability)
Do you have to adjust maintenance dose in a person with impaired renal function?
Yes! Maintenance dose = (clearance X desired plasma conc.) ÷ bioavailability (F)
How do you calculate renal function? What is the equation?
Calculate renal function with creatinine clearance… Creatinine clearance = [(140-age) X (weight in Kg)] ÷ [72 X (Serum creatinine in mg/dL)]