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Integrated physiology > A.D.M.E > Flashcards

A.D.M.E Flashcards

1
Q

what is pharmacokinetics

A

the study and characterisation of drug absorption, distribution, metabolism and excretion

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2
Q

what is pharmacodynamics

A

what the body does to the drug as opposed to what the drug does to the body

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3
Q

what does knowledge of pharmacokinetic properties of a particular drug tell us

A

what dose to give, how often to give it, how to change the dose in certain medical conditions, how some drug interactions occur

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4
Q

what is absorption

A

the movement of a drug from the site of administration to the bloodstream

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5
Q

3 mechanisms by which drugs may cross membranes

A

passive diffusion, facilitated diffusion, active transport

passive diffusion most common

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6
Q

distribution

A

process of reversible transfer of the drug from the bloodstream to other areas of the body. if the drug does not return to the blood, it has been eliminated.

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7
Q

what is the rate and extent of distribution determined by

A
  • how well perfused the organs/tissues are
  • binding of the drug to plasma proteins and tissue components
  • permeability of tissue membranes to the drug
  • ion trapping
  • P-glycoproteins (efflux mechanism)
  • pKa
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8
Q

volume of distribution

A

convenient method of describing how well a drug is removed from the plasma and distributed to the tissues. however, it doesn’t provide any specific info about where the drug is concentrated in a particular organ.
a large Vd implies wide distribution, or extensive tissue binding, or both. conversely, ionised drugs that are trapped un plasma will have small Vd

definition; amount of fluid that would be required to contain the drug in the body at the same concentration as in the blood or plasma.

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9
Q

bioavailability

A

the proportion if a dose that reaches the systemic circulation in a chemically unaltered form

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10
Q

elimination half life

A

t1/2
the time required to reduce the plasma concentration to one half of its initial value
can be used to estimate for how long a drug should be stopped if a patient has toxic drug levels

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11
Q

clearance

A

Cl; volume of plasma in the vascular compartment cleared of drug per unit time by the process of metabolism and excretion

drug can be cleared by renal excretion or by metabolism or both

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12
Q

drug metabolism

A

drugs are detoxified by a set of xenobiotic-metabolising enzymes;
-cytochrome P450 oxidases, primarily found in the liver

enzymatic action may also convert prodrugs (inactive) to active state
availability of these enzymes is more than sufficient to efficiently metabolise most drugs

exceptions
small number of drugs where concentrations seen in real life use are high enough o saturate the eliminating enzymes e.g. phenytoin, salicylates and ethanol

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13
Q

excretion

A

elimination of the molecule in its unchanged form, mainly via kidney.

1) glomerular filtration
2) tubular secretion/reabsorption

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14
Q

drug interactions

A

occur when the effect of the drug is modified by presence of another agent

modifying agents- other drugs, diet, smoking, alcohol
most drug interactions involve changes to the absorption, distribution, metabolism or excretion of drugs

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15
Q

pharmacokinetic vs pharmacodynamic interactions

A

pharmacokinetic; amount of drug in blood is altered

pharmacodynamic; amount of drug in blood remains the same, but its effect is altered

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16
Q

drug absorption interactions

A

one drug make the absorption of another drug;
faster or slower, less or more complete

mechanisms;
pH, gastric emptying and intestinal motility, physiochemical interactions

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17
Q

drug distribution interactions

A

displacement e.g. drug A and B both compete to bind to the same plasma protein

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18
Q

drug metabolism interactions

A

one drug changes the rate of metabolism of another drug
induction; A increases the rate of metabolism of B, blood concentrations of B fall below normal therapeutic levels. B becomes ineffective

inhibition; A reduces the rate of metabolism of B, blood concentrations increase above that which is safe, B becomes toxic

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19
Q

drug excretion interactions

A

Drug A increases or reduces the excretion of drug B

blood levels of B fall below or rise above normal therapeutic range
becomes either ineffective or toxic

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20
Q

absorption requirements for passive diffusion

A

water solubility- almost all drugs are sufficiently water soluble to undergo passive diffusion
lipid solubility- some do lack necessary lipid solubility . in practise, diffusion depends mainly on lipid solubility

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21
Q

efficient molecules of passive diffusion

A

hydrocarbons, anaesthetics, alcohols, lipids, most drugs

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22
Q

inefficient drugs for passive diffusion

A

carbohydrates, proteins. ionised molecules

23
Q

facilitated diffusion

A

selective gateway allows entry of one group of molecules, but excludes all others

24
Q

active transport

A

structurally selective, energy requiring, can operate against concentration gradient

25
Q

patient characteristics which could effect distribution

A

oedema, dehydration, obesity, pregnancy - dose needs to be modified accordingly

26
Q

what compartments can drugs distribute into

A

plasma, interstitial fluid, intracellular fluid

27
Q

incomplete oral bioavailability

A
  1. failure of disintegration or dissolution
  2. chemical, enzymatic or bacterial attack
  3. failure of absorption and p-gp efflux
  4. first pass metabolism in gut wall or liver
28
Q

phases of metabolism

A

phase 1- functionalisation
chemical change-addition of a new functional group
most frequently oxidation, but also reduction
renders the drug more conductive to phase 2

phase 2- conjugation
conjugative or synthetic addition off a polar molecule
drug becomes water soluble and amenable to renal excretion

29
Q

cytochrome P450

A

phase 1 oxidative reactions typically involve a cytochrome P450 monooxygenase (CYP)
nomenclature based on nucleic acid and amino acid homology

(nomenclature is genetically based; no functional implication)

CYPs have family, sub family and specific gene e.g. CYP2D6

30
Q

first pass metabolism in the gut wall

A

intestinal epithelium is rich in drug metabolising enzymes (CYPs, mainly CYP3A4)

CYP450 activity in intestinal epithelium relative to liver
duodenum 50%
jejunum 30%
ileum 10%
colon 25
31
Q

kidneys and excretion

A

excretion irreversibly removes drugs or metabolites from the body
the kidneys are the principal organ of excretion, but the liver, GI tract and lungs also may play important roles

excretion by the kidney;1. glomerular filtration - glomerular structure, size constraints, protein binding 
2. tubular reabsorption/secretion 
acidification/alkalisation 
active transport, competitive/saturable
organic acids/bases
protein binding
32
Q

biliary excretion

A

bile formed in large volumes in the liver->most of the water reabsorbed->concentrated bile stored in the gall bladder->bile excreted into the upper small intestine

33
Q

drug interactions-changes in pH

A

stomach-pH is variable
antacids pH^, alcohols and some foods cause acidic secretion pH to decrease

small and large intestine
pH always near neutral
no significant changes seen

34
Q

gastric emptying and intestinal motility

A

drug absorption from small intestine is much more efficient than from the stomach, however if drug A alters rate of gastric emptying
- rate of absorption of drug B also altered

35
Q

physio chemical interactions

A

two drugs bind together within GI contents and then neither is absorbed. e.g. polyvalent cations, cholestyramine, charcoal

36
Q

CYP450

A

gradual onset and offset;
onset–accumulation of inducing agent and increase in enzyme production
offset- elimination of inducing agent and decay of enzymes. result in reduction of plasma concentration of substrate drugs

37
Q

withdrawal of inducer

A

patient taking barbiturates and warfarin, barbiturates cause induction-warfarin clearance increased]warfarin dose titrated above normal dose, blood levels now normal
barbiturate suddenly withdrawn and replaced by valproate
warfarin clearance falls- blood levels rise above normal- patient dies

38
Q

beneficial use of induction

A

new born infants have poorly developed hepatic metabolic enzymes
conjugate bilirubin inefficiently-some become jaundiced
small doses of barbiturates can be used to induce the liver enzymes and clear the bilirubin

39
Q

inhibition

A

not just opposite of induction:
induction- additional CYP450 in the liver
inhibition-no reduction in quantity of CYP450 -existing CYP450 made less effective
probably most significant of all interactions-potentially fatal

40
Q

fruit juices

A

grapefruit juice contains antioxidants that inhibit CYP3A4 in the gut wall and liver. leads to increased blood levels of terfenadine and some calcium channel blockers

cranberry juice contains various antioxidants including flavonoids which are known to inhibit CYP450- warfarin levels may rise significantly

41
Q

drug excretion interactions

A

mechanism of urinary excretion ; dimple filtration, active secretion (have limited capacity)
mechanism for active secretion; acids, bases,, saturation of mechanisms by one of the competing drugs -other is secreted less efficiently

42
Q

most important physio-chemical properties

A

solubility in water, solubility in lipids, electrical charge, size

43
Q

physiological factors

A

nature of barriers/membrane
blood supply
site of action
rate of removal

44
Q

patient factors

A

age, size/weight, gender. pregnancy, medical condition, ethnicity

45
Q

benefits of drugs by passing the liver

A

will not get metabolised by liver (many drugs get therapeutically altered while being metabolised by the liver)

ways you can do this is by giving the drug rectally

46
Q

factors effecting bioavailability

A

formulation, physio-chemical properties, physiological factors, patient factors

47
Q

what is the therapeutic index

A

ratio of the minimum toxic concentration to the median effective concentration

48
Q

how to calculate Vd

A

Vd (L)=dose (gr)/C (gr/L)

or C=dose/Vd

49
Q

blood brain barrier

A 
specialist cells (glial and endothelial) separate the blood vessels from the cerebrospinal fluid (CSF)
exact nature varies depending on location 
provides additional protection to CNS while regulating transport of essential; molecules ad maintaining a stable environment (homeostasis)
50
Q

how would weight gain effect Vd

A

increase in fat (e.g.), depending on drugs solubility, the above may contribute to an increase in Vd, which in tur will require increasing the dose to maintain drug concentration within effective range

51
Q

excreting organs in the body

A

kidneys, skin, lungs liver

52
Q

what may direct a molecule towards excretion by kidney rather than liver

A

polar molecules get readily filtrated out by the kidney. amphiphilic drugs are more likely to get excreted by the liver into the bile,

53
Q

how do CYPs differ from one another

A

substrate, substrate affinity and enzymatic activity

genetic makeup

Integrated physiology (8 decks)

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