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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 Popular FACTSSS Probenecid (gout) Furosemide Azetazolamide Celecoxib Thiazides Sulfonamide antibiotics Sulfasalazine (IBS, rheum arth) Sulfonylureas (diabetic drug)