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ICPP > ICPP 10 Pharmacokinetics > Flashcards

ICPP 10 Pharmacokinetics Flashcards

1
Q

How to calculate oral availability

A

F = Fa x Fg x Fh

Fa - fraction of dose absorbed
Fg - fraction of drug passing through gut wall w/o metabolism
Fh - fraction of drug passing through liver w/o metabolism

Is a fraction or percentage

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2
Q

What are the four main processes in drug therapy?
What do each of these mean?

A
  • Absorption: site of administration > bloodstream
  • Distribution: bloodstream > body tissues
  • Metabolism: drug is chemically modified
  • Excretion: drug is eliminated from body
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3
Q

What processes allow drugs to enter?

A

Absorption
Distribution

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4
Q

What processes allow drugs to exit?

A

Metabolism
Excretion

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5
Q

What is enteral drug administration?

A

Delivery into internal environment of body - GI tract

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6
Q

What is parenteral drug administration?

A

Delivery via all routes that are not in GI tract

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7
Q

difference between pharmacodynamics and pharmacokinetics

A

pharmacodynamics - what the drug does to the body
pharmacokinetics - what the body does to the drug

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8
Q

what are the 4 main process of drug therapy?

A
  • pharmaceutical - is the drug getting into the patient?
  • pharmacokinetics - is the drug getting to its target site?
  • pharmacodynamics - is the drugs producing the required pharmacological effect?
  • therapeutic - is the pharmacological effect being translated into a therapeutic effect?
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9
Q

what are the types of drug administration

A

paraentral - intrathecal, intramuscular, transdermal, inhalation, intravenous, subcutaenous
enteral - rectal, oral, sublingual

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10
Q

how are drugs absorbed?

A

drug mixes with chyme + enters small intestine

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11
Q

where does most drug absorption occur?

A

small intestine

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12
Q

why is there little drug absorption in the stomach

A

thick layer of mucosa layer

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13
Q

what process facilitates drug absorption?

A
  • passive diffusion
  • facilitated diffusion
  • primary/secondary active transport
  • pinocytosis
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14
Q

what drug absorption is via passive diffusion?

A

lipophilic drugs e.g. steroids
weak acids/bases

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15
Q

what drug absorption is via facilitated diffusion?
outline the process

A
  • molecules with net ionic charge
  • based on electrochemical gradients through solute carrier transporters - OATs (-) or OCTs (+)
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16
Q

what mechanisms do solute carrier transporters enable drug transport by?

A

facilitated diffusion
secondary active transport

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17
Q

describe drug absorption by secondary active transport

A
  • via solute carrier transporters
  • electrochemical gradient needed
  • no ATP
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18
Q

physicochemical factors affecting drug absorption

A
  • surface area (GI length)
  • drug lipophilicity (pKa)
  • density of SLC expression in GI
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19
Q

physiological factors affecting drug absorption

A
  • blood flow - increases after meal
  • GI mobility - decreases after meal
  • food
  • pH - low pH can destroy some drugs
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20
Q

what factors affect drug absorption in terms of first pass metabolism by GI and liver?

A

gut lumen - enzymes can denature drugs
gut wall/liver - some drugs can metabolised by cytochrome p450s and conjugating enzymes (phase I + II enzymes)

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21
Q

what in the gut wall/liver affects drug absorption?

A

cytochrome p450s + conjugating enzymes
metabolised some drugs

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22
Q

what is bioavailability?

A

the fraction of the drug which gets to a specific body compartment

23
Q

what is the most common reference compartment for bioavailability?

A

CVS - circulation

24
Q

what is the bioavailability reference for CVS compartment and why?

A

IV bolus = 100%
no physical/metabolic barriers to overcome

25
Q

how to calculate bioavailability

A

amount reaching systemic circulation orally/total of SAME drug given IV

AUCoral/AUCiv

26
Q

outline the first stage of drug distribution

A

bulk flow
diffusion

27
Q

what factors affect drug distribution?

A

drug molecule hydrophilicity:
- lipophilic drugs move freely across cell membrane
- hydrophilic drugs need EC gradient
drug binding to plasma and/or tissue proteins

28
Q

describe drug binding to plasma and/or tissue proteins

A
  • only free drug molecules can bind to target sites
  • binding to plasma/tissue decreases the free drug available for binding
29
Q

what is Vd?

A

apparent volume of distribution

30
Q

how to calculate Vd

A

Vd = drug dose/[plasma drug] at time 0
in litres

31
Q

what do smaller and larger Vd values indicate?

A

Smaller - less penetration of interstitial/intercellular fluid compartment
Larger - more penetration of interstitial/intercellular fluid compartment

32
Q

what factors affect Vd?

A
  • changes in regional blood flow
  • pregnancy
  • paediatrics/neonates
  • geriatrics
  • cancer patients
33
Q

what is drug elimination?
where does it occur mainly

A

metabolism - liver
excretion - kidneys

34
Q

outline hepatic drug metabolism

A

via phase I + II enzymes (cytochrome p450s and cytosolic enzymes)
cytochrome P450 - generalists > metabolise wide range of molecules
cytosolic enzymes - generalists but faster kinetics

35
Q

what is action of phase I and II enzymes

A

metabolism drugs
increase ionic charge > enhances renal elimination

36
Q

what factors affect drug metabolism?

A
  • age
  • sex
  • general health/disease
  • other drugs which induce or inhibit CYP450s
37
Q

What does HRH stand for?

A

Hepatic
Renal
Heart diseases

38
Q

what effect can grapefruit juice have on drug metabolism?

A

inhibits CYP450 > less drug is metabolised

39
Q

What are the three processes in renal excretion

A
  • glomerular filtration
  • active (proximal) tubular secretion
  • passive (distal) tubular reabsorption
40
Q

describe drugs in glomerular filtration

A

unbound drugs enter glomerulus via Bowman’s capsule for filtration - 20% of renal blood flow

41
Q

describe drugs in proximal tubular secretion

A
  • remaining 80% of blood via peritublar capillaries
  • charged + polar molecules actively transported back by OATs or OCTS
42
Q

what is clearance?

A

the volume (Vd) of plasma that is completely cleared of the drug per unit time (ml/min)

rate of elimination of drug from body

43
Q

what is drug half life (t1/2)?

A

time it takes for drugs plasma conc to decrease by half

44
Q

what is the relationship between half life, Vd and clearance?

A

t1/2 is dependent on Vd and CL
- if CL increases + Vd stays the same > t1/2 decreases
- if CL stays the same + Vd increases > t1/2 increases

45
Q

what happens if the DCT is acidic?

A

weak acids pronate > become neutral charge > reabsobed

46
Q

what happens if DCT is basic?

A

weak bases lose protons > become neutral charge > reabsorbed

47
Q

what effect does acidic vs alkaline urine have on weak acids?

A

Acidic - increase absorption
Alkaline - decreases absorption

48
Q

what effect does acidic vs alkaline urine have on weak acids?

A

acidic - decreases absorption
alkaline - increases absorption

49
Q

what is linear elimination kinetics

A

rate of elimination is proportional to plasma drug conc. per unit time

50
Q

what happens when the elimination process becomes saturated?

A

rate limited
becomes zero order kinetics

51
Q

what are zero order kinetics?

A
  • drugs near therapeutic dose with saturation kinetics
  • elimination is constant
52
Q

what is the clinical importance of zero order kinetics?

A

small dose changes can:
- produce large increase in drug plasma conc.
- lead to serious toxicity

53
Q

Outline phase I reactions of metabolism

A

Introduce more polar groups on drug e.g. OH or NH2 by:
- oxidation
- hydrolysis
.
Carried out by cytochrome P450s

54
Q

What do OATs and OCTs transport?

A
  • OATs: deprotonated weak acids A-
  • OCTs: protonated weak bases BH+

ICPP (18 decks)

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