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ICPP 10 Pharmacokinetics Flashcards

(54 cards)

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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?

Study These Flashcards
A

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

23
Q

what is the most common reference compartment for bioavailability?

Study These Flashcards
A

CVS - circulation

24
Q

what is the bioavailability reference for CVS compartment and why?

Study These Flashcards
A

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

25
how to calculate bioavailability
amount reaching systemic circulation orally/total of SAME drug given IV AUCoral/AUCiv
26
outline the first stage of drug distribution
**bulk flow** **diffusion**
27
what factors affect drug distribution?
**drug molecule hydrophilicity**: - lipophilic drugs move freely across cell membrane - hydrophilic drugs need EC gradient **drug binding to plasma and/or tissue proteins**
28
describe drug binding to plasma and/or tissue proteins
- only free drug molecules can bind to target sites - binding to plasma/tissue decreases the free drug available for binding
29
what is Vd?
apparent volume of distribution
30
how to calculate Vd
Vd = drug dose/[plasma drug] at time 0 in litres
31
what do smaller and larger Vd values indicate?
**Smaller** - less penetration of interstitial/intercellular fluid compartment **Larger** - more penetration of interstitial/intercellular fluid compartment
32
what factors affect Vd?
- changes in regional blood flow - pregnancy - paediatrics/neonates - geriatrics - cancer patients
33
what is drug elimination? where does it occur mainly
**metabolism** - liver **excretion** - kidneys
34
outline hepatic drug metabolism
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
what is action of phase I and II enzymes
metabolism drugs increase ionic charge > enhances renal elimination
36
what factors affect drug metabolism?
- age - sex - general health/disease - other drugs which induce or inhibit CYP450s
37
What does HRH stand for?
Hepatic Renal Heart diseases
38
what effect can grapefruit juice have on drug metabolism?
inhibits CYP450 > less drug is metabolised
39
What are the three processes in renal excretion
- glomerular filtration - active (proximal) tubular secretion - passive (distal) tubular reabsorption
40
describe drugs in glomerular filtration
unbound drugs enter glomerulus via Bowman's capsule for filtration - 20% of renal blood flow
41
describe drugs in proximal tubular secretion
- remaining 80% of blood via peritublar capillaries - charged + polar molecules actively transported back by OATs or OCTS
42
what is clearance?
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
what is drug half life (t1/2)?
time it takes for drugs plasma conc to decrease by half
44
what is the relationship between half life, Vd and clearance?
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
what happens if the DCT is acidic?
weak acids pronate > become neutral charge > reabsobed
46
what happens if DCT is basic?
weak bases lose protons > become neutral charge > reabsorbed
47
what effect does acidic vs alkaline urine have on weak acids?
**Acidic** - increase absorption **Alkaline** - decreases absorption
48
what effect does acidic vs alkaline urine have on weak acids?
**acidic** - decreases absorption **alkaline** - increases absorption
49
what is linear elimination kinetics
rate of elimination is proportional to plasma drug conc. per unit time
50
what happens when the elimination process becomes saturated?
rate limited becomes zero order kinetics
51
what are zero order kinetics?
- drugs near therapeutic dose with saturation kinetics - elimination is constant
52
what is the clinical importance of zero order kinetics?
small dose changes can: - produce large increase in drug plasma conc. - lead to serious toxicity
53
Outline phase I reactions of metabolism
Introduce more polar groups on drug *e.g. OH or NH2* by: - oxidation - hydrolysis . Carried out by cytochrome P450s
54
What do OATs and OCTs transport?
- **OATs**: deprotonated weak acids A- - **OCTs**: protonated weak bases BH+

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