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MAD Exam 2 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

pharmacokinetics

A

the discipline that describes the absorption, distribution, metabolism, and excretion of drugs
*how the body affects the drugs

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2
Q

criteria for getting a drug to work

A
  1. unbound and active form of drug has to bind to receptor
  2. usually, the drug gets to the receptor via the plasma
  3. usually, the concentration of the drug at the active site decreases over time
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3
Q

steady state serum level

A

serum concentration when the amount of drug going into the patient = amount going out of the patient
*must be continued dosing to acheive

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4
Q

loading dose

A

one-time dose to get to a therapeutic level quickly
*usually followed by smaller amounts of continued dose

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5
Q

volume of distribution - definition

A

THEORETICAL volume that the amount of drug administered would occupy (it it were uniformly distributed) to provide the same concentration as it currently is in the blood plasma

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6
Q

volume of distribution - equation

A

Vd = amount of drug in body / concentration

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7
Q

concentration =

A

amount / volume

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8
Q

what will INCREASE volume of distribution (Vd)

A

extensive binding and/or distribution to the TISSUES

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9
Q

what will DECREASE volume of distribution (Vd)

A

increased binding to SERUM proteins

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10
Q

clearance - definition

A

represents a volume of plasma from which the drug is eliminated per unit time (volume/time)

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11
Q

rate of elimination = ? (for a first order process)

A

rate of elim = clearance x concentration

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12
Q

clearance - equation (for a first order process)

A

clearance = Vd x Ke
*note - Ke is the elimination rate constant

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13
Q

zero-order elimination of a drug

A

a CONSTANT AMOUNT is eliminated over time, regardless of concentration
*ex = 1 mg is eliminated every hour
*linear plot

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14
Q

first-order elimination of a drug

A

a constant PROPORTION is eliminated over time
*amount eliminated decreases as concentration decreases
*ex = 20% is eliminated every hour
*logarithmic plot
*MOST drugs are first-order

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15
Q

half-life - definition

A

time required to decrease the amount of drug in the body by HALF

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16
Q

half-life - equation

A

half-life = (0.7 x Vd) / clearance

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17
Q

how many half lives does it take to achieve steady state

A

~5 half-lives for ANY DOSAGE CHANGE (starting or stopping drugs)

18
Q

are loading doses affected by changes in elimination

A

NO (but maintenance doses do)

19
Q

how can you decrease concentration variability when giving a drug

A

give the drug more frequently

20
Q

how does albumin affect volume of distribution

A

albumin is a serum protein, and many medications bind to it, SO:
*LOW serum albumin means more drug going into the tissues (HIGHER Vd)
*HIGH serum albumin means more drug staying in the plasma (LOWER Vd)

21
Q

routes of absorption (how drugs cross membranes)

A
  1. passive diffusion
  2. facilitated passive diffusion
  3. active transport
  4. pinocytosis (rarely)
22
Q

benefits of absorption of drug in small intestine

A

*largest surface area for drug absorption
*membranes more permeable than those in stomach

23
Q

bioavailability (f) - definition

A

fraction of unchanged drug reaching SYSTEMIC CIRCULATION following administration from any route

24
Q

bioavailability (f) for IV administration

A

= 1 (100% bioavailability)

25
Q

bioavailability (f) - equation

A

f = AUCoral / AUCiv

26
Q

loading dose- equation, including bioavailability

A

= (concentration x Vd) / f

27
Q

maintenance dose - equation, including bioavailability

A

= (concentration x clearance) / f
*note - concentration is the TARGET concentration

28
Q

first pass metabolism

A

the fraction of drug lost in absorption due to metabolism in the gut wall and liver

29
Q

what is the main goal of drug metabolism

A

make the compound easier to excrete (by making it more water-soluble)

30
Q

phase I reactions of metabolism in the liver

A

introduce or unmask a functional group (-OH, -NH2, -SH) via oxidation, reduction, or hydrolysis

31
Q

phase II reactions of metabolism in the liver

A

conjugation with glucuronic acid, sulfuric acid, acetic acid, or an amino acid to make a polar compound

32
Q

what is the most important phase I enzyme system

A

cytochrome P450 (CYP-450)

33
Q

cytochrome P450 interactions

A
  1. substrate
  2. inhibitor
  3. inducer
34
Q

cytochrome P450 - substrates

A

drugs that are a substrate of a CYP enzyme are metabolized via this pathway

35
Q

cytochrome P450 - inhibitor

A

drugs that inhibit a CYP enzyme DECREASE the metabolism of active medications for that enzyme
*increase the concentration of active drug (compared to what you would normally see)

36
Q

cytochrome P450 - inducer

A

drugs that INDUCE CYP enzymes increase the metabolism of active medications that are substrates for that enzyme
*decrease the concentration of active drug (compared to what you would normally see)

37
Q

drugs that INDUCE CYP450

A

rifampin
phenobarbitol
carbamazepine
phenytoin

38
Q

drugs that INHIBIT CYP450 (“magic rack”)

A

macrolides
amiodarone
grapefruit juice
INH
cimetidine
ritonavir
acute alcohol
ciprofloxacin
ketoconazole

39
Q

common substrates of CYP450

A

warfarin
phenytoin
oral contraceptives

40
Q

pharmacogenetics

A

the effects of a SINGLE genetic marker

41
Q

pharmacogenomics

A

the COLLECTIVE influence of variability across the genome to modulate an individual’s drug response profile

42
Q

what is the principle organ for excretion of drugs

A

KIDNEYS (for water-soluble substances)
-involves filtration, secretion, and reabsorption

MAD Exam 2 (37 decks)

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