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23 Cards in this Set

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what reflects enzyme affinity?
Km = [S] when V = 1/2 Vmax
(lower the Km, higher the affinity)
plot of 1/[S] (x-axis) vs 1/V (y-axis):

-y-intercept?
-x-intercept?
-slope?
y-intercept = 1/Vmax (larger --> smaller Vmax)
x-intercept = -1/K

slope = Km / Vmax

*note: x = 0 represents [substrate] = infinity (x = -1/[S]);
enzyme kinetic graph (y = 1/V; x = -1/[S]) - an enzyme has a higher affinity, which intercept is changed how?
x-intercept is more negative (lower Km, higher affinity)
enzyme kinetic graph (y = 1/V; x = -1/[S]) - an enzyme has a higher Vmax, which intercept is changed how?
y-intercept is smaller (higher Vmax)
enzyme kinetic graph (y = 1/V; x = -1/[S]) - a competitive inhibitor is introduced, what changes how?
slope inceases (Vmax/Km)
Vmax unchanged - Y intercept
Km increases (less affinity) - X intercept decreases
enzyme kinetic graph (y = 1/V; x = -1/[S]) - a noncompetitive inhibitor is introduced, what changes how?
slope increases (Vmax/Km)
Km is unchanged (same affinity) - X intercept
Vmax decreases - y-intercept increases
what is the effect on potency and efficacy of competitive inhibitors? noncompetitive?
competitive inhibitors - decrease potency (amount of drug needed for given effect; directly proportional to affinity)
noncompetitive inhibitors - decrease efficacy (max effect drug can produce)
what are high efficacy drugs?
efficacy = max effect drug can have

analgesics
antibiotics
antihistamines
decongestants
what are high potency drugs?
potency = amount of drug needed for given effect; directly proportional to affinity

chemotherapeutics
antihypertensives
antilipids
what is Vd? what dz processes can change a drugs Vd?
Vd = total amount of drug in body / plasma drug concentration

drugs that bind plasma protein can have Vd altered by liver & kidney dz (decreased protein --> increased Vd); may be decreased by dehydration

Low Vd (4-8L) - distributed in blood
Medium Vd - in extracellular space/body water
High Vd - in all tissues, lipophilic
how to calculate clearance?
CL = rate elimination / plasma concentration = Vd x Ke (elimination constant) = 0.7*Vd / t-half

**t-half is a property only 1st order elimation has
how to calculate t-half life? how many half lives to reach steady state?
t-half is a property of 1st order kinetics

t-half = 0.7*Vd / CL (clearance)

4-5 half lives to reach a steady state
how to calculate loading dose? maintenance dose?
Loading dose = Cp x Vd / F (bioavailability fraction)

Maintenance dose = Cp x CL / F
what drugs are eliminated by Zero order elimination?
PEA (round shaped, like 0)

Phenytoin
Ethanol
Aspirin (at high/toxic concentrations)
how to tx overdose of weak acids? weak bases?
weak acids - trapped when H+ dissociates so tx w/HCO3-

weak bases - trapped when it accepts an H+, so tx w/ammonium chloride
common weak acid overdoses? tx?
phenobarbital
methotrexate
aspirin

tx w/bicarb --> alkalinize to trap the weak acid in the urine
common weak base overdoses? tx?
amphetamines

tx w/ammonium chloride --> acidify to trap in urine
phase I vs phase II metabolism?
phase I --> slightly polar, water souble metabolites (often still active)
(reduction, oxidation, hydrolysis)

phase II = conjugation --> yields very polar, inactive metabolites (renally excreted)
(Glucuronidation, Acetylation, Sulfation)
do geriatric patients lose phase I or phase II metabolism first?
phase I
which phase (I or II) of metabolism yields renally excreted products? which yields still active products?
phase II - renally excreted
phase I - still active
cytochrome P450 catalyzes which phase (I or II) of drug metabolism?
phase I (reduction, oxidation, hydrolysis)
how is therapeutic index calculated? are higher or lower values safer?
TI = LD50 / ED50 (MEDIAN lethal & effective doses)

higher TI are safer
**make note, uses median, NOT mean
Sulfa drugs

-reaction?
-mneumonic & drugs
reaction: fever, UTI, pruritic rash, Stevens-Johnson syndrome, hemolytic anemia, thrombocytopenia, agranulocytosis, urtiaria
sx range from milde to life-threatening

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