general

Question 1

Km?

Answer 1

Km = [S] at 1/2 Vmax

Question 2

how is Km related to enzyme affinity for substrate?

Answer 2

inversely

Question 3

how is Vmax related to enzyme concentration?

Answer 3

directly proportional

Question 4

what does a sigmoid enzymatic curve mean?

Answer 4

cooperative kinetics (e.g. hemoglobin/O2 binding)

Question 5

what are the intercepts on the Lineweaver-Burk plot?

Answer 5

y intercept = 1/Vmax - as moves up, Vmax decreases

x intercept = 1/-Km - as moves closer to 0, Km increases (affinity decreases)

Question 6

how do reversible competitive inhibitors affect enzyme kinetics?

Answer 6

increase Km, Vmax unchanged
decrease potency

** can be overcome by increase in [S]

Question 7

how do irreversible competitive inhibitors affect enzyme kinetics?

Answer 7

decrease Vmax, Km unchanged
decrease efficacy

** cannot be overcome by increase in [S]

Question 8

how do noncompetitive inhibitors affect enzyme kinetics?

Answer 8

decrease Vmax, Km unchanged
decrease efficacy

** cannot be overcome by increase in [S]

Question 9

formula for Vd?

Answer 9

Vd = (amt of drug in body) / (plasma drug concentration)

Question 10

what drug types have low Vd?

Answer 10

large/charged molecules
bound to plasma proteins

–> confined to blood compartment

Question 11

what drug types have medium Vd?

Answer 11

small hydrophilic molecules

–> confined to ECF

Question 12

what drug types have high Vd?

Answer 12

small lipophilic molecules
especially those bound to tissue protein

–> distrib to all tissues, including fat

Question 13

formula for clearance?

Answer 13

CL = (rate of drug elim) / (plasma drug concentration)
CL = Vd * Ke 
Ke = elimination constant

Question 14

how many half lives does it take for a drug to reach steady state (with constant infusion)?

Answer 14

4-5
(takes 3.3 half lives to reach 90% steady state)

** independent of dosage or dose frequency

Question 15

formula for half life?

Answer 15

T1/2 = (0.693 * Vd) / CL

Question 16

formula for loading dose?

Answer 16

LD = (Cp * Vd) / F

Question 17

formula for maintenance dose?

Answer 17

MD = (Cp * CL * t) / F

t = time between doses

Question 18

which drugs exhibit zero order elimination?

Answer 18

PEA = zero-shaped
phenytoin
ethanol
aspirin

Question 19

which drugs are weak acids? what does this mean clinically?

Answer 19

phenobarb
MTX
aspirin
TCAs

** “trapped” in basic environment: OD can be tx’ed with bicarb

Question 20

which drugs are weak bases? what does this mean clinically?

Answer 20

amphetamines

** “trapped” in acidic environment: OD can be tx’ed with ammonium chloride

Question 21

phase I of drug metabolism?

Answer 21

CYP450: reduction, oxidation, hydrolysis
usually yields slightly polar water-soluble metabolites
products often still active

** lost first in geriatric pts

Question 22

phase II of drug metabolism?

Answer 22

conjugation: glucuronidation, acetylation, sulfation
yields very polar, inactive metabolites –> renal excretion

** slow acetylators: increased SEs from drugs

Question 23

efficacy vs potency?

Answer 23

efficacy = maximal effect produced by drug - Vmax
potency = amt of drug needed for given effect - EC50

Question 24

relationship bw diazepam and flumazenil?

Answer 24

diazepam = agonist
flumazenil = competitive antagonist
(GABA rcptr)

Question 25

relationship bw NE and phenoxybenzamine?

Answer 25

NE = agonist
phenozybenzamine = noncompetitive antagonis
(alpha rcptr)

Question 26

relationship bw morphine and buprenorphine?

Answer 26

morphine = full agonist
buprenorphine = partial agonist

Question 27

formula for therapeutic index?

Answer 27

TI = TD50 / ED50

higher TI = safer

** dig, lithium, theophylline, warfarin - LOW TI, less safe