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23 Cards in this Set
- Front
- Back
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what reflects enzyme affinity?
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Km = [S] when V = 1/2 Vmax
(lower the Km, higher the affinity) |
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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]); |
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enzyme kinetic graph (y = 1/V; x = -1/[S]) - an enzyme has a higher affinity, which intercept is changed how?
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x-intercept is more negative (lower Km, higher affinity)
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enzyme kinetic graph (y = 1/V; x = -1/[S]) - an enzyme has a higher Vmax, which intercept is changed how?
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y-intercept is smaller (higher Vmax)
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enzyme kinetic graph (y = 1/V; x = -1/[S]) - a competitive inhibitor is introduced, what changes how?
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slope inceases (Vmax/Km)
Vmax unchanged - Y intercept Km increases (less affinity) - X intercept decreases |
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enzyme kinetic graph (y = 1/V; x = -1/[S]) - a noncompetitive inhibitor is introduced, what changes how?
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slope increases (Vmax/Km)
Km is unchanged (same affinity) - X intercept Vmax decreases - y-intercept increases |
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what is the effect on potency and efficacy of competitive inhibitors? noncompetitive?
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competitive inhibitors - decrease potency (amount of drug needed for given effect; directly proportional to affinity)
noncompetitive inhibitors - decrease efficacy (max effect drug can produce) |
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what are high efficacy drugs?
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efficacy = max effect drug can have
analgesics antibiotics antihistamines decongestants |
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what are high potency drugs?
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potency = amount of drug needed for given effect; directly proportional to affinity
chemotherapeutics antihypertensives antilipids |
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what is Vd? what dz processes can change a drugs Vd?
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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 |
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how to calculate clearance?
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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 |
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how to calculate t-half life? how many half lives to reach steady state?
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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 |
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how to calculate loading dose? maintenance dose?
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Loading dose = Cp x Vd / F (bioavailability fraction)
Maintenance dose = Cp x CL / F |
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what drugs are eliminated by Zero order elimination?
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PEA (round shaped, like 0)
Phenytoin Ethanol Aspirin (at high/toxic concentrations) |
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how to tx overdose of weak acids? weak bases?
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weak acids - trapped when H+ dissociates so tx w/HCO3-
weak bases - trapped when it accepts an H+, so tx w/ammonium chloride |
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common weak acid overdoses? tx?
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phenobarbital
methotrexate aspirin tx w/bicarb --> alkalinize to trap the weak acid in the urine |
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common weak base overdoses? tx?
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amphetamines
tx w/ammonium chloride --> acidify to trap in urine |
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phase I vs phase II metabolism?
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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) |
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do geriatric patients lose phase I or phase II metabolism first?
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phase I
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which phase (I or II) of metabolism yields renally excreted products? which yields still active products?
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phase II - renally excreted
phase I - still active |
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cytochrome P450 catalyzes which phase (I or II) of drug metabolism?
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phase I (reduction, oxidation, hydrolysis)
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how is therapeutic index calculated? are higher or lower values safer?
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TI = LD50 / ED50 (MEDIAN lethal & effective doses)
higher TI are safer **make note, uses median, NOT mean |
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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 Popular FACTSSS Probenecid (gout) Furosemide Azetazolamide Celecoxib Thiazides Sulfonamide antibiotics Sulfasalazine (IBS, rheum arth) Sulfonylureas (diabetic drug) |
