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Year 2 > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Define absorption

A

Process of transfer from the site of administration into the general or systemic circulation

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2
Q

Name the routes of medicinal administration

A
  1. Oral
  2. IV
  3. Intra Arterial
  4. Intramuscular
  5. Subcutaneous
  6. Inhalational
  7. Topical
  8. Sublingual
  9. Rectal
  10. Intrathecal
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3
Q

What must all drugs do when delivered into the body

A

Cross at least one membrane in its passage from site of administration to the general circulation (including intracellular sites)

Exception of IV or IA

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4
Q

Four different ways substances can move across the plasma membrane

A
  1. Passive diffusion
  2. Diffusion through pores or ion channels
  3. Carrier mediated processes
  4. Pinocytosis
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5
Q

What property do drugs need to have in order to move passively across the plasma membrane

A

Lipid solubility to cross phospholipid bilayer

Rate of diffusion is proportional to concentration gradient, area and permeability of membrane and inversely proportional to thickness

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6
Q

What property do drugs need to have to move down ion channels

A

Be very small water-soluble molecules

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7
Q

What substance do carrier proteins need to move substances into a cell and why

A

ATP

Substances moved against their concentration gradient

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8
Q

What are carrier proteins also called

A

ATP-binding cassette

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9
Q

How many carrier proteins (ABCs) do we have

A

49

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10
Q

What is so special about P-gp

A

An ABC that removes a wide range of drugs from cytoplasm to extracellular side

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11
Q

What drug inhibits P-gp

A

Verapamil to increase conc. of anti-cancer drugs in the cytoplasm,

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12
Q

How do substances move down carrier proteins passively

A

facilitated diffusion

or co-transport to move it against a conc. gradient

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13
Q

How many SLCs (solute carriers) are there

A

300

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14
Q

Where is OAT1 found

A

Kidney

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15
Q

Role of OAT1

A

Secretes Penicillin and Uric acid

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16
Q

What drug blocks the action of OAT 1

A

Probenecid so uric acid is excreted

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17
Q

What drugs tend to be taken up by cells via pinocytosis

A

Amphotericin into the liposome

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18
Q

What is the basic property for most drugs

A

Ionisation as they can be either weak acids or bases

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19
Q

What property do ionised drugs have

A

Water-soluble

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20
Q

What property do non-ionised drugs have

A

Lipid soluble

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21
Q

What is the PKa of a drug

A

pH at which half of the substance is ionised and half is unionised

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22
Q

Where are weak acids best absorbed

A

Stomach

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23
Q

Where are weak bases best absorbed

A

Intestines

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24
Q

pH in urine vs plasma and what is the consequence of an aspirin overdose because of this

A

Lower in urine than plasma

Aspirin overdose is a weak acid so will be largely un-ionised and reabsorbed into plasma

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25
Q

How do we prevent aspirin overdose

A

Alkalinise urine with IV bicarbonate to reduce reabsorption of aspirin + elimination

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26
Q

Easiest delivery of drugs

A

Oral route

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27
Q

Why is the oral route efficient

A

Large SA and high blood flow of small intestines gives rapid and complete absorption of oral drugs

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28
Q

What is the major determinant of drug absorption

A

Drug structure

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29
Q

What properties do drugs need to have to maximise absorption

A
  1. Drugs need to be lipid-soluble to be absorbed from gut
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30
Q

What is the problem with highly polarised drugs

A

Only partially absorbed and most passes into faeces (Olsalazine)
Drug must disintegrate and dissolve to be absorbed rapidly

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31
Q

When is Olsalazine given

A

Colonic IBD

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32
Q

Problem with drugs that are faced with low pH of the stomach

A

They may be unstable

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33
Q

How do we overcome drugs that may become unstable at low pH levels

A

They are formulated to dissolve slowly or have a coating resistant to the acidity of the stomach (enteric coating)

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34
Q

How can gastric emptying be delayed

A

Food, drugs or trauma

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35
Q

How can gastric emptying be faster

A

Gastric surgery

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36
Q

What four major barriers do drugs have to pass to reach circulation

A

Intestinal Lumen
Intestinal Wall
Liver
Lungs

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37
Q

What three bonds can be spilt in the stomach

A

Peptide
Ester
Glycosidic Bonds

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38
Q

Role of colonic bacteria in drug metabolism

A

Hydrolysis and reduction of drugs

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39
Q

What is a special property of the upper intestinal walls

A

Rich in cellular enzymes

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40
Q

Name a cellular enzyme in the upper intestinal wall

A

MAO (Mono Amine Oxidases)

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41
Q

How can drug absorption be limited in the intestines

A

Luminal membrane of enterocytes contains P-gp which moves drugs back out into the intestinal lumen

42
Q

How does extensive bowel surgery affect drug absorption

A

Poor oral absorption as little surface left

43
Q

What circulation do drugs absorbed from the intestines move down and to where

A

Splanchnic circulation to the liver

44
Q

How do we avoid hepatic drug metabolism

A

Deliver drug to region of gut not drained by splanchnic

45
Q

How long does IV, Interosseous take until effect

A

30-60 seconds

46
Q

How long does inhalation and endotracheal drug delivery take for it to have an effect

A

2-3 minutes

47
Q

How long does it take for sublingual drug delivery to take effect

A

3-5 minutes

48
Q

How long does it take for intramuscular drug delivery to take effect

A

10-20 minutes

49
Q

How long does it take for subcutaneous drug delivery to take effect

A

15-30 minutes

50
Q

How long does it take for rectal delivery to take effect

A

5-30 minutes

51
Q

How long does it take for drugs to take effect by indigestion

A

30-90 minutes

52
Q

Why do we need potent, non-irritant drugs to move across human epidermis

A

Effective barrier to water-soluble compounds which can limit rate of absorption of lipid soluble drugs

53
Q

How do we deliver drugs transcutaneously

A

Using transdermal patches

54
Q

When is intradermal and subcutaneous drug delivery used

A

Used for local effect (local anaesthetic) or contraceptives

55
Q

Why are intradermal and subcutaneous drug deliveries effective

A

Avoids barrier of stratum corneum

56
Q

How is intradermal and subcutaneous drug delivery limited

A

Blood flow

57
Q

What two factors effect intramuscular drug delivery

A

Blood flow

Water solubility

58
Q

How are intramuscular drugs delivered

A

Depot injection

Incorporate lipophilic formulation which releases drugs over days

59
Q

Disadvantage of intranasal drugs

A

Low level of proteases and drug metabolising enzymes

60
Q

Advantage of intranasal drugs

A

Good SA

61
Q

Benefits of inhalation drugs

A

Large SA

Blood flow

62
Q

Limitations of inhalation drugs

A

Risk of toxicity to alveoli

Delivery of non-volatile drugs

63
Q

What drugs are used inhalation ally

A

Volatiles
General Anaesthetics
Locally acting drugs

64
Q

Why are asthma drugs non-effective inhalation-wise

A

Only 5% delivered to small airways

Non-volatile

65
Q

Describe the equilibrium shifts with IV drug injections

A
  1. High initial plasma conc.
  2. Rapid perfusion of drug into tissue
  3. Drug perfusion slows
  4. Plasma conc. decreases
  5. Conc. in highly perfused tissues decrease
66
Q

Where does reversible protein binding occur

A

To albumin

67
Q

Why is protein binding needed

A

Lowers free conc. of drug and releases bound drug when plasma conc. decreases

68
Q

How is albumin-bound drug released

A

Redistribution

Elimination

69
Q

What is the consequence of irreversible binding of drugs to plasma proteins

A

Basically eliminated as they can’t enter circulation

70
Q

What property of drugs allow ease of movement from blood to brain

A

Lipid-soluble

71
Q

What drugs struggle to moves across BBB

A

Water-soluble

72
Q

How do mechanisms prevent too high a conc. of drugs in the brain

A

Efflux transporters being present

73
Q

How are drugs removed from the brain other than efflux transporters

A

Diffusion into plasma via Active Transport in CSF

74
Q

What drug property is important in pregnancy

A

Lipid-soluble, SMALL drugs that can readily move across the placenta

LARGE molecules don’t cross the placenta

75
Q

What is the issue with drugs moving through placenta

A

Blood flow through it is slow so slow equilibration with foetus

76
Q

What drug will not pass the placenta

A

Heparin

77
Q

Why are drugs not easily metabolised by foetus

A

Low levels of drug metabolising enzymes so rely on maternal elimination

78
Q

How do opiates given to the mother during labour effect the newborn

A

Persist in them as they have to eliminate them (causes sleepy baby)

79
Q

Define metabolism

A

Transformation of drug molecule into a different molecule

80
Q

Define excretion

A

Molecule is expelled in liquid, solid or gaseous waste

81
Q

What happens during metabolism of drugs

A

Drugs converted to water-soluble products and removed in urine

82
Q

What would be the consequence is lipid-soluble drugs remain lipid soluble

A

Reabsorbed

83
Q

What is phase I drug metabolism

A

Transformation of drug to more polar metabolite by exposing or adding a functional group (-OH, NH2)

Oxidation and reduction reactions by CYP450

84
Q

Where are CYP450 found

A

SER

85
Q

Which CYPs are involved in drug metabolism

A

CYP1-4

86
Q

What two environmental factors induce P450 enzymes

A

Smoking

Alcohol

87
Q

What drugs/foods inhibit P450

A

Grapefruit

Cimetidine

88
Q

differences in CYPs

A

They metabolise at different rates

89
Q

Where else can drugs be metabolised

A

Plasma, lung or gut

90
Q

What enzyme metabolises Ethanol and in which phase

A

Alcohol dehydrogenase - phase I

91
Q

What enzymes inactivates noradrenaline

A

Monoamine Oxidase

92
Q

What enzyme inactivated 6-nercaptopurine

A

Xanthine

93
Q

What are phase II reactions

A

Involves formation of a covalent bond between drug or its phase I metabolite and endogenous substrate

94
Q

Property of products form phase II reactions

A

Less active

95
Q

Where do phase II reactions take place

A

Cytoplasm
Mitochondrial
Microsomal

96
Q

Difference between products of phase I and phase II reactions

A

Phase I - Active or inactive

Phase II - Inactive. water soluble

97
Q

What type of drugs are excreted in fluids

A

Low molecular weight polar compounds

98
Q

What drugs are excreted in solids

A

High MWT compounds excreted in bile

99
Q

What drugs are excreted in gases

A

Volatiles

100
Q

Formula for total excretion

A

Glomerular filtration + tubular secretion - reabsorption

101
Q

Describe faecal excretion of drugs

A

high weight molecules taken up by HEPATOCYTES
Into BILE
Drugs reabsorbed and re-enter hepatic portal vein

Year 2 (155 decks)

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