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Pharmacology > quantitative pharm > Flashcards

quantitative pharm Flashcards

1
Q

what is the criteria for a clinically significant pharmocdynamic interaction?

A

drug B must have a narrow therapeutic window?

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2
Q

what is the criteria for a clinically significant pharmcokinetic interaction?

A

drug B must have a steep-dose response curve

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3
Q

how can haemodynamic effects control drug metabolism?

A

a drug like propanolol decreases cardiac output, this reduces blood flow through the liver, this would slow the metabolism of drugs reaching the liver via first bypass metabolism (e.g. lidocaine)

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4
Q

what is a type A reaction?

A

this is a reaction which is dose related

it can be predicted purely on the pharmacological effects of a drug.

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5
Q

give examples of a type A interactions?

A

verampil and constipation
NSAIDS and dyspepsia
Beta blockers and asthma

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6
Q

what is a type B reaction>

A

those are unpredictable immune responses, and they cause the highest mortality

e.g. penicillin and analphylaxis
statins and rhabdomylosis
agranulocytosis and carbimazole
sulfa drugs or anti-convulsants and Steven Johonson’s syndrome

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7
Q

what it a type C reaction?

A

this is dose related but over time, due to drug accumulation

e.g. steroids and catarcts

NSAIDs and intersistial nephritis

Benzodiazpaenes and dependance

anthracyclines and cardiomypathy

linezolid and optic neuropathy (drug used to treat MRSa)

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8
Q

what is the equation for partition coefficient

A

concentration in organic solvent/ concentration in aqeous phase

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9
Q

how does partition coefficient relate to absorption?

A

there is a direct correlation, the higher lipid solubility and rate of absorption

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10
Q

what does partition co-efficient refer to?

A

the lipid solubility of a substance

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11
Q

what is pKA of a drug?

A

this is the pH at which there is equal amounts of ionised and non-ionised forms of a drug

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12
Q

what is the acid dissociation constant?

A

ka = (H+ * A-)/HA

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13
Q

what type of pKA will a strong acid have?

A

low pKA q

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14
Q

what type of pKA will a weak base have?

A

a low pKA

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15
Q

what is first pass metabolism?

A

when a drug absorbed from the GI tract, reaches the liver via the portal vein and undergoes biotransformation before reaching the general circulation

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16
Q

how can we avoid first pass metabolism?

A

drug is not given orally, instead drug is give sublingually or rectally to bypass the GI tract

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17
Q

what are the merits of rectal administration?

A
  • bypasses first pass metabolism
  • useful in children
  • can be used for certain irritants
  • good if patient unable to take medication (e.g. unconscious or vomitting)
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18
Q

what are the merits of oral administration?

A

lipid solubility and ionisation (Weak acids well absorbed from the stomach

the intestines has a massive surface area due to its microvilli and this increases its rate of absorption

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19
Q

how will damage to the intestines effect rate of absorption?

A

it will reduce the rate of absorption, because microvilli are lost, the microvilli surface area aids in increasing the rate of absorption

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20
Q

how does the rate of gastric emptying effect absorption

A

the faster the gastric emptying the faster the absorption, because absorption is faster in the intestines rather than the stomach

metoclopramide - which increases rate of gastric emptying - increases drug absorption
opiates- which decrease the rate of gastric emptying reduce drug absorption (because they the drug reach the small intestines

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21
Q

what does bulk effect have on gut absorption?

A

reduces drug absorption becauses reduces drug concentration and impairs access to mucosa

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22
Q

how does splanchinc flow affect the rate of absorption from the gut?

A

this has no affect on drug absorption

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23
Q

what are the two necessary considerations important for tablets?

A

disintegration time:
- this is the time taken for the tablet to break down into little pieces

dissolution rate:
- this is the rate at which the drug dissolves (which is influenced by particle size and crystal form)

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24
Q

what are the two necessary considerations important for tablets?

A

disintegration time:
- this is the time taken for the tablet to break down into little pieces

dissolution rate:
- this is the rate at which the drug dissolves (which is influenced by particle size and crystal form)

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25
Q

what is the purpose of the binder in a tablet

A

makes the tablet cohesive and holds it together

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26
Q

what is the purpose of a surfactant in a tablet?

A

aids wetting and dissolution of drug

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27
Q

what is the purpose of a disintegrate?

A

this allows rapid breakdown of tablet after swalloing

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28
Q

what is the purpose of the filler

A

makes the drug large enough to handle and compress

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29
Q

roughly what percentage does the active drug form in a tablet?

A

25%

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30
Q

what is bioavailability? and how can we measure it?

A

is measurement of the rate and extent of a therapeutically active drug that reaches the systematic circulation
can be quantified as the area under the curve of plasma concentration over time

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31
Q

what is meant by bioequivalence?

A

is if two drugs administered in the same molar dosages have the same bioavailability after administration having the similar effects (Efficacy and safety)

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32
Q

what are the merits of paraenteral administration?

A

this is literally any route which does not utilise the GI tract

  • when rapid action is required
  • when the drugs penetrate the mucosa with difficulty
  • when drugs are destroyed in the stomach/gut
  • irritants
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33
Q

why is absorption from the lungs good?

A

because the lungs have a massive surface area, they have a rich blood supply and thin membranes

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34
Q

what determines absorption from the lungs?

A

particle size determines absorption from the lungs:

  • small particles likely to deposit in alveoli
  • whilst larger particles likely to deposit in extra thoracic region
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35
Q

in transdermal administration, what determines the rate of absorption?

A

the lipid permeability of the drug, because the skin can provide a barrier

36
Q

what determines the rate and extent of absorption from the eye?

A

the time the drug remains in the cul-de-sac and perconeal tear film

37
Q

how are low-molecular weight, soluble drugs distributed in the body?

A

they’re equally distributed throughout the body water

38
Q

what is non-uniform distribution of drug determined by?

A

lipid/water solubility of the drug and its ability to pass through the membrane

39
Q

what is the volume of distribution?

A

the volume a drug would occupy if it is evenly distributed through that volume at the concentration measured in the plasma

40
Q

what values of VD do drugs that specifically accumulate in certain tissues have?

A

they have large VD

because recall VD= dose given/plasma concentration

41
Q

what is first order kinetics?

A

this is when the rate of drug absorption or excretion is proportional to the concentration of drug at the site of administration or in the plasma

occurs in non-saturatable processes

42
Q

what is first order kinetics?

A

this is when the rate of drug absorption or excretion is proportional to the concentration of drug at the site of administration or in the plasma

occurs in non-saturatable processes

43
Q

what is first order elimination?

A

this is when the drug because it is eliminated exponentially, when the second drug dosage is given, it reaches a higher plasma concentration than first dosage (cumulation effect). however there is a limit to drug accumulation

44
Q

what is zero order elimination?

A

this is the amount of drug excreted is independent to the drug concentration, this usually occurs in saturable mechanisms. in this cause no plateau with dosage is reached, and drug accumulation can occur indefinitely

45
Q

what is the equation for zero order excretion?

A

Cp= -Kel * t + Co

  • Kel can be calculated from the gradient of a graph
46
Q

how does plasma protein binding effect activity of a drug?

A

plasma protein bound drug is inactive

47
Q

how does plasma protein binding affect absorption?

A

maybe enhanced by the sink effect

48
Q

how does plasma protein binding effect drug distribution?

A

the drug will be distributed according to how this binding protein is distributed

49
Q

how does plasma protein binding affect storage?

A

essentially plasma binding proteins act as a storage for the drug

50
Q

how does plasma binding protein affect elimination?

A

no globular filtration of bound drug, does not affect tubular secretion

51
Q

what limits the rate of distribution of a polar drug?

A

membrane permeability

52
Q

what limits the rate of distribution for a less polar drug?

A

blood perfusion

53
Q

how are drugs with low molecular weights excreted?

A

assuming they are not bound to protein, they’re filtered at the glomerulus, the concentration of drug in the filtrate is equal to the concentration of drug in the plasma

54
Q

how are drugs with low molecular weights excreted?

A

assuming they are not bound to protein, they’re filtered at the glomerulus, the concentration of drug in the filtrate is equal to the concentration of drug in the plasma

55
Q

what is drug clearance?

A

this is the volume of drug cleared from plasma per unit time

  1. first assumption is that the body is a single compartment
  2. that the drug is cleared using first order kinetics
56
Q

what is the equation for rate of clearance

A

CT= Vd * Kel

57
Q

what influences reabsorption at the glomerulus?

A

the lipid solubility and the degree of ionisation of the drug (which is affected by the urine pH)

58
Q

what are the effects of acidic urinary pH

A

causes the reabsorption of acidic drug and excretion of basic drugs

59
Q

what are the affects of an alkaline urinary pH

A

causes reabsorption of alkaline drug and excretion of acidic pH

60
Q

how do we alkalise urine?

A

POTASSIUM CITRATE and sodium bicarbonate

61
Q

how do we acidify urine?

A

NH4CL and ascorbic acid

62
Q

how do we increase salicylate excretion?

A

forced alkaline diuresis

63
Q

how does kidney disease affect drug elimination?

A

kidney disease reduces excretion rate, by reducing renal clearance

64
Q

how is kidney function usually measured?

A

this is measured via GFR (creatinine clearance), and we’d adjust our dosages accordingly

65
Q

what is biotransformation?

A

this is the termination of pharmacological activity by inducing more polar substances with reduced lipid solubility. this increases their excretion. although the biotransformation of some drugs can lead to toxic metabolites or their metabolites can be equally as active or more active (e.g. if the drug is designed as a pro-drug)

66
Q

where does biotransformation occur?

A

in the smooth endoplasmic reticulum, of the liver because it contains the p450 cytochrome system (Responsible for oxidation)

67
Q

what are the two steps involved in biotransformation?

A

functionalisation and conjugation

68
Q

what happens to larger compounds?

A

those are preferentially excreted in bile. so they enter the enter-hepatic circulation.

they’re transferred from blood to bile via active transport
in the liver they become conjugated, the conjugate can
1. be excreted in faeces
2. deconjugated by bacterial enzymes

deconjugated drugs re-enters circulation and then transferred to bile and becomes re-conjugated- and this is the enterohepatic circulation, where the drug becomes maintained in the enteric pool:

this increases the half life of the drug and its associated hepatoxicity

69
Q

what is Gray baby syndrome?

A

this is a rare but severe side effect to the intravenous injection of chloramphenicol in infants. because the infant’s metabolism is not fully develop, they can not conjugate the drug, and this leads to the build up of toxic metabolites (glucarodination)

70
Q

how does dosage requirement in elderly differ?

A

dosage requirement is significantly less because of reduced renal clearance, as renal clearance is reduced as part of the normal ageing process

because of reduced clearance and metabolism it also means that drugs have a much narrower therapeutic index

71
Q

what are the two uses of Probenecid?

A

used in gout: this is because it prevents the tubular reabsorption of uric acid, and therefore, increases it excretion. (blocks an organic anionic transporter)

used in penicillin: this drug blocks the tubular secretion of penicillin and this increases its concentration

72
Q

which drug does acetylator status effect?

A

isoniazid, this drug is metabolised by acetylation. two forms of the enzyme can do this reaction - hence two different half lives for the drug can exist (thus a bimodal distribution) of half life

73
Q

which drug does atypical plasma cholinesterase effect?

A

suxamethonium (again a bimodal distribution of half life)

74
Q

which drugs does renal clearance have the most affect on their half lives?

A

on drugs which are excreted unchanged (those are usll

75
Q

which drugs does renal clearance have the most affect on their half lives?

A

on drugs which are excreted unchanged (those are usually hydrophilic polar substance)

76
Q

what happens with repeated use of b2 agonists in the treatment of asthma?

A

the B2 receptors become down regulated

77
Q

what happens in the repeated use of thyroxin?

A

beta receptors in the heart increase

78
Q

what is receptor densensitation, and when does it occur?

A

this occurs with repeated administration of an agonist, it is also known as agonist induced receptor deactivation

  • this is seen with nicotine
79
Q

what does can ibuprofen and NSAIDs cause?

A

GI tract haemorrhage, increased BP and renal impairment

80
Q

what can digoxin cause?

A

dysrhythmias

81
Q

what levothyroxine cause?

A

coronary artery disease

82
Q

what can prednisone cause and other GCs?

A

peptic ulcer disease

83
Q

what can verampil and dilitizaem cause?

A

congestive heart failure

84
Q

what disease can propanolol and other B adrenergic antagonists cause?

A

congestive heart failure and COPD

85
Q

what disease can propanolol and other B adrenergic antagonists cause?

A

congestive heart failure and COPD

86
Q

what is the biggest cause in the variation in required dosages?

A

drug metabolism

Pharmacology (17 decks)

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