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principles of disease > Drug Absorption > Flashcards

Drug Absorption Flashcards

Discuss the physico-chemical factors that affect the transfer of drugs across cell membranes. Discuss the factors that affect absorption of a drug from the GI tract Discuss the medical importance of first pass metabolism. Discuss the benefits of intravenous, topical and inhaled medication.

1
Q

Pharmaceutical process

A

Get the drug into the patient

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2
Q

Get the drug to the site of action

A

Pharmacokinetic process

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3
Q

Produce the correct pharmacological effect

A

Pharmacodynamic process

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4
Q

Produce the correct therapeutic effect

A

Therapeutic process

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5
Q

the 4 basic factors to determine drug pharmacokinetics.

A

Absorption
Distribution
Metabolism
Elimination

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6
Q

how can drugs be administered

A

oral, IV, subcutaneous (insulin injection), intramuscular, rectal, inhalation, nasal, transdermal

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7
Q

what is Absorption is defined as

A

the process of movement of unchanged drug from the site of administration to the systemic circulation.

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8
Q

what is therapeutic response related to

A

plasma concentration of a drug

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9
Q

what is Tmax

A

the time of peak concentration

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10
Q

Cmax

A

the peak concentration

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11
Q

what is AUC

A

Area under the curve - relates to the amount of drug that actually gets into the systemic tsystem

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12
Q

higher Tmax

A

the earlier the conc. peaks

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13
Q

what happens when dose is increased

A

not affect time to peak conc. - however the Cmax is increased

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14
Q

what is the name of the active range of a drug?

A

the therapeutic range

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15
Q

what happens above/below the the therapeutic range

A

above - toxicity

below - no pharmacological action

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16
Q

what is the therapeutic index

A

a measure of the range at which a drug is safe and active.

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17
Q

bioavailability

A

the proportion of a drug or other substance which enters the circulation when introduced into the body and so is able to have an active effect

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18
Q

what is the Henderson-Hasselbalch

A

The relationship between the local pH and the degree of ionisation

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19
Q

what is the ability of a drug to diffuse across a lipid barrier

A

lipid-water partition coefficient

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20
Q

how quickly will a highly lipid soluble drug diffuse across a membrane

A

rapidly diffuse

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21
Q

will a non lipid soluble drug be absorbed

A

no

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22
Q

how much is absorbed via inhalation

what is it better for

A

5-10%

volatile agents

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23
Q

how would a drug pass across a lipid barrier

A

be lipid soluble

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24
Q

what are the main drivers of drug filtration

A

the hydrostatic and osmotic pressure across the membrane

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25
Q

what GI factors effect adsorption

A

motility - speed to reach absorption site (area of bowel)
food - can enhance or impair absorption
illness - especially pain reduces absorption rate

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26
Q

what is first pass metabolism

A

its when some of the drug is metabolised before it reaches the systemic circulation (ADME becomes AMDME)

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27
Q

what are some of the benefits of sublingual (under tongue)

A

by passes first pass metabolism

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28
Q

what are the benefits of rectal medicine

A

use drugs that irritate stomach

absorption tends to be slow bypass first pass metabolism

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29
Q

what is transdermal

A

a patch on skin
controlled release
avoids first pass metabolism

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30
Q

what is the difference between a topical and IV drug administration

A

iv is more direct, less drug is needed to get same effect, absorption is more rapid higher Tmax

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31
Q

what should the unionised form of drugs do

A

pass across a membrane until it reaches equilibrium

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32
Q

a drug with high lipid solubility will

A

will rapidly diffuse across a cell membrane.

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33
Q

what is motility

hoe dose it effect GI absorption

A

Speed of gastric absorption will affect speed at which drug reaches site of absorption - small intestine

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34
Q

how dose food effect GI absorption

A

Can enhance or impair rate of absorption.

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35
Q

how does illness effect GI absorption

A

Migraine reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs.

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36
Q

what factors affect tissue distribution

A 
Plasma protein binding
Tissue perfusion
Membrane characteristics
Transport mechanisms
Diseases and other drugs
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37
Q

how does plasma protein effect distribution

A

the more drug that binds to protein the less that is biologically INACTIVE

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38
Q

what can bioavailability be effected by

A 
Renal failure
Hypoalbuminaemia
Pregnancy
OTHER DRUGS
Saturability of binding
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39
Q

why is it important

A

if bioavalibility is low (high drug binding)

then a small change in drug binding can have a FUCKING HUGE change in free drug (toxicity?)

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40
Q

what is Vd

A

volume of distribution

volume of plasma that would be necessary to account for the total amount of drug in a patient’s body

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41
Q

what happens as Vd increases

A

the ability of the drug to diffuse into and through membranes.

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42
Q

if a drug could penetrate any membrane the Vd would be…

A

42L - volume of fluid in human

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43
Q

what is clearance (cl)

A

the theoretical volume from which a drug is completely removed

MEASURE OF ELIMINATION

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44
Q

what is half life

A

the time taken for the drug conc. to decline by half

45
Q

what doses half life depend on

A

Vd and Cl

0.7xVd/Cl

46
Q

if a half life increases so will

A

toxicity

47
Q

what is steady state conc.

A

the concentration that sits in the therapeutic range after chronic administration

48
Q

what dose drug elimination determine

what is it made up of

A

the length of drug action

metabolism
excretion

49
Q

what are the primary organs for drug excretion

A

the kidneys

50
Q

what are the 3 principles of excretion

A

glomerular filtration
passive tubular
reabsorption

51
Q

what is glomerular filtration

A

is how much liquid and waste are passing through the kidneys

52
Q

passive tubular excretion

what can this lead to

A

eliminating protein bound cationic and anionic drugs

is In high conc. so can lead to reabsorption

53
Q

what is biliary secretion

A

liver - secreted in to the bile

some reabsorbed - entero-hepatic circulation

54
Q

what dose metabolism in the liver lead to

A

conjugation of the drug which means its not reabsorbed

liver damage may reduce this = toxicity

55
Q

what is drug metabolism

A

the biochemical modification of pharmaceutical substances by living organisms (ENZYMES)

56
Q

what dose metabolism do

A

turn lipid soluble and non-polar substances

POLAR AND WATER SOLUBLE for excretion

57
Q

where dose metabolism occur

A

LIVER, lining of the gut, the kidneys and the lungs.

58
Q

what drugs might be activated after metabolism

A

PRODRUGS

first past metabolism

59
Q

what are the two phases of metabolism

A

phase 1 (POLARITY) = drug becomes activated or inactivated

phase 2 (WATER SOLUBILITY) = forms conjugation products

60
Q

what are the phase 1 reactions

what is their goal

A

oxidation
reduction
hydrolysis

to increase the polarity of a substance

61
Q

what is cytochrome P-450

A

enzymes are the most important super family of metabolising enzymes.

62
Q

what is drug specificity determined by

A

the isoform of the cytochrome P-450

63
Q

what is a isoform

A

a protein formed from a gene just (different splicing)

64
Q

what is CYP3A4

A

enzyme in human liver

diazepam, methadone

65
Q

what is CYP2D6

A

responsible for the metabolism of some antidepressants

Reduced or absent expression is found in 5-10% of the population (immune)

66
Q

what is CYP1A2

A

induced by smoking and is important in the metabolism of theophylline.

67
Q

what is conjugation

A

increases the water solubility and enhances excretion of the metabolised compound.

68
Q

what does conjugation attach

A

glucuronic acid, glutathione, sulphate or acetate

69
Q

what is another name for phase 2

A

GLUCURONIDATION

70
Q

what factors effect metabolism

A 
Other drugs/herbals/natural substances
Genetics
Hepatic blood flow
Liver disease
Age
Sex
Ethnicity
Pregnancy
71
Q

what happens if a enzyme is endued

A

Increased metabolism of drugs metabolised by that enzyme

Resulting in decreased drug effect

72
Q

what causes enzyme induction

A

othe compounds

other drugs

73
Q

what happens when enzymes are inhibited

A

often lead to toxicity

may be irreversible

74
Q

what drugs cause enzyme inhibition

A

common food, drugs
HERBAL MEDICINES

erythromycin
clarithromycin

75
Q

what is the importance of pharmacogenetics

A

inter-individual differences in gene expression are common

therefore

metabolising enzymes are often expressed in multiple forms

76
Q

what is the expression of multiple metabolising drugs called

A

Genetic Polymorphisms

77
Q

how dose age effect metabolism

A

in the young and old

renal function might be deficient

78
Q

how does sex effect metabolism

A

Responsiveness to certain drugs is different for men and women

Pregnancy – induction of certain drug metabolizing enzymes occurs in second and third trimester

79
Q

what do monoclonal antibodies do

A

delivery of a toxin, cytokine or other active drug

80
Q

what is a suspension

what is it good for

A

drug particles in a liquid phase

make a small volume

drugs that are unpalatable - in a sugary syrup

can go in a nasal gastric tube

81
Q

what 3 factors determine dosage regimes

A

dose
frequency
timing

(administering technique?)

82
Q

what is the classification of ADR onset

A

acute
sub-acute
latent

83
Q

what is the classification of ADRs

A 
type A - augmented
tB - bizarre 
tC - chronic
tD - delayed 
tE - end of treatment 
tF - failure of treatment
84
Q

what are predisposing factors of ADRs

A 
age 
sex
race/genetic polymorphism
inter-current disease
multiple drug therapy's
85
Q

what are type A reactions

A

entirely predictable dose dependent

pharmacological action

Easily reversible

86
Q

what are examples of type A reactions

A

bradycardia - beta-blockers

hypoglycaemia - insulin

87
Q

what are the two types of TYPE A ADRs

A

Augmentation of the primary effect

Secondary effect

88
Q

how are ADRs reported

A

yellow card app

89
Q

what is reported

A

ADRs affecting Black Triangle Drugs

All significant or unusual adverse drug reactions

90
Q

what is the secondary effect

A

an effect that is not on the target area but still makes sense due to the pharmacology of the drug

dry mouth with tricyclic antidepressants

91
Q

what are the two common reasons for Type A ADRs

when do they occur

A

Pharmacokinetic variation
Pharmacodynamic variation

as a result of disease

92
Q

what is teratogenicity

A

abnormal foetus malformations due to in utero exposure

ALL DRUGS AVOIDED DURING PREGNANCY

93
Q

what are the important factors in type B ADRs

A

more common with macromolecules

patient has history of asthma , eczema

94
Q

how is a drug allergy/ hypersensitivity reaction formed

A

The first dose acts as the antigen
Body produces the antibody
Subsequent antigen-antibody reaction

95
Q

what type of effect is teratogenicity

A

a delayed effect - long time after treatment

96
Q

what are some teratogenic agents

A

Cytotoxins
Vitamin A
Anti-thyroid drugs
Steroids

97
Q

what are some long term effects of ADRs

what type is this

A

Semi-predictable

Steroid induced osteoporosis

Opiate dependence

TYPE C

98
Q

when do Type C ADRs occur

A

is related to the duration of treatment as well as the dose

99
Q

what are some examples drugs most likely to be involved

A

Warfarin
Erythromicin
Clarithromicin
Cyclosporin

100
Q

what type of interactions can occur

A 
drug on drug
herbal
food
drink
pharmacogenetics
101
Q

The Drug whose Activity is effected by such an Interaction is called the..

A

object drug

102
Q

The agent which precipitates a drug-drug interaction is referred to as the

A

the Precipitant

103
Q

what are some examples of good drug interactions

A

treatment of hypertension

treatment of Parkinsonism

104
Q

drug - dug interactions effect how many people

A

3-30% in hospital

9.2-70% in GP

105
Q

what traits do drugs that are most likely to be involved in drug-drug interactions

A

All these drugs are potent with a narrow therapeutic index

small change in blood levels can induce profound toxicity

106
Q

what is a drug-drug interaction

A

interaction is defined as the modification of a drugs effect by prior or concomitant administration of another substance

107
Q

what are some predisposing conditions

A 
no. of medications
old
young 
very ill
chronic conditions
108
Q

what chronic conditions could cause drug-drug interactions

A 
liver disease
renal impairment
diabetes mellitus
epilepsy
asthma
109
Q

what is the importance of therapeutic drug monitoring

A

to make sure that potent drugs with narrow therapeutic windows don’t become highly toxic

principles of disease (18 decks)

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