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Year One - Principles of Disease > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What do pharmaceutical processes involve?

A

Getting the drug to the patient

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2
Q

What do pharmacokinetic processes involve?

A

Getting the drug to the site of action

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3
Q

What do pharmacodynamic processes involve?

A

Producing the correct pharmacological effect

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4
Q

What do therapeutic processes involve?

A

Producing the correct therapeutic effect

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5
Q

What are the four basic gator that determine drug pharmacokinetics?

A

Absorption

Distribution

Metabolism

Elimination

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6
Q

What is absorption?

A

Process of movement of unchanged drug from the site of administration to the systemic circulation

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7
Q

What are the seven routes of absorption?

A

Oral

Subcutaneous

Intramuscular

Sublingual

Rectal

Inhalation

Transdermal

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8
Q

What does oral absorption involve?

A

Taking a drug orally so that it can pass through the intestinal tissue and into the circulatory system

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9
Q

What does subcutaneous absorption involve? Why is this method advantageous? Why is this method disadvantageous?

A

Injecting the drug into the tissue layer between the skin and muscle

Only requires a small volume of the drug. It avoids first pass metabolism

Some drugs are not well absorbed with this route - those that are insoluble in water

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10
Q

What does intramuscular absorption involve? Why is this method advantageous? Why is this method disadvantageous?

A

Injecting the drug into muscle

Fast, due to the great blood supply in muscle. Only requires a small volume of the drug. It avoids first pass metabolism

Some drugs are not well absorbed with this route - those that are insoluble in water

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11
Q

What does sublingual absorption involve? Why is this method advantageous? Why is this method disadvantageous?

A

Administering drugs via the mouth

Avoids first pass metabolism as they will directly enter circulation

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12
Q

What does rectal absorption involve? Why is this method advantageous? Why is this method disadvantageous?

A

Uses the rectum as a route of administration

Avoids first pass metabolism

Absorption is slow

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13
Q

What does inhalation absorption involve? Why is this method advantageous?

A

Inhaling and breathing in the medication. Suited to volatile drugs.

Relatively rapid. Small amount of the drug is needed to have a huge effect . Less side effects

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14
Q

What does transdermal absorption involve? Why is this method advantageous? Why is this method disadvantageous?

A

Delivers a drug into systemic circulation across the skin

Avoids first pass metabolism. Controlled release

Few substances well-absorbed

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15
Q

Why is intravenous not required as an absorption?

A

Straight into blood stream

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16
Q

What is Tmax?

A

Time to peak concentration.

The more the rapid the rate of absorption, the smaller the Tmax value.

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17
Q

What is Cmax?

A

The peak concentration.

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18
Q

What effect does increasing dose of a drug have on Cmax and Tmax?

A

Increasing the dose does not affect the time at which peak concentration is reached but does increase the peak concentration

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19
Q

What is AUC?

A

The area under the drug concentration-time curve, which represents the amount of drug which reaches the systemic circulation

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20
Q

What is the therapeutic range?

A

The range of concentration in which the drug is active

Below this range, there will be insufficient or no pharmacological action.

Above this range, toxicity will occur

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21
Q

What is bioavailability of a drug?

A

The amount of drug which is available for action

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22
Q

How can a drug have 100% bioavailability?

A

If it is given intravenously

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23
Q

What affects a drugs ability to pass through physiological barriers?

A

Particle size

Lipid solubility

pH

Ionisation

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24
Q

How does particle size affect a drugs ability to pass through physiological barriers?

A

Small particle size tend to diffuse more rapidly across cell membranes than those that are large

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25
Q

How does ionisation affect a drugs ability to pass through physiological barriers?

A

Those that don’t ionise in aqueous environments tend to diffuse more rapidly across cell membranes than those that do

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26
Q

How does pH affect a drugs ability to pass through physiological barriers?

A

Most drugs are weak acids or bases, which means that their degree of ionisation depends on the pH of the environment

Both ionised and un-ionised forms will be present, with the ionised form of the drug being unable to pass across the membrane and the un-ionised form being able to pass across the membrane until equilibrium is reached and an equal concentration is on either side of the membrane.

An acidic drug will be more concentrated in the compartment with a high pH and a basic drug will be more concentrated in the compartment with a low pH.

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27
Q

How does lipid solubility affect a drugs ability to pass through physiological barriers?

A

Those that are lipid soluble diffuse more rapidly across cell membranes than those that are lipophobic

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28
Q

What is the lipid-water partition coefficient?

A

Measures a drugs ability to diffuse across a lipid barrier.

This is the ratio of the amount of drug which dissolves In the lipid and water phase when they are in contact

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29
Q

What are the four ways drugs can move across the cell membrane?

A

Passive diffusion

Active diffusion

Facilitated diffusion

Filtration

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30
Q

What is passive diffusion?

A

Method of diffusion that occurs along the concentration gradient, from a high to low concentration.

Requires no energy or carrier

Non-selective method that depends on lipid solubility and the degree of ionisation

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31
Q

What is active diffusion?

A

Method of diffusion that occurs against the concentration gradient

Requires a carrier and energy

Specific method that usually transports ions. To undergo active transport, drugs must resemble the naturally occurring compounds

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32
Q

What is facilitated diffusion?

A

Method of diffusion that occurs along the concentration gradient, from a high to low concentration.

Requires a carrier but no energy. The carrier is structurally specific to the molecule that they transport across the membrane

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33
Q

What is filtration?

A

Normally occurs through channels in the cell membrane

Transports molecules of a low molecule size and weight

Driving force of passage is the hydrostatic or the osmotic pressure differences across the membrane

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34
Q

What gastrointestinal factors effect absorption?

A

Gut motility - speed of gastric absorption will affect the speed at which the drug reaches the site of absorption

Food - enhance or impair rate of absorption

Illness - disease that affects GI system or liver function

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35
Q

What factors affect absorption?

A

Formulation

Ability to pass through physiological barriers

Gastrointestinal factors

First pass metabolism

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36
Q

What is first pass metabolism? What does it depend upon?

A

The concentration of a drug is greatly reduced before it reaches the systemic circulation, as the drug is already metabolised.

Acid and enzymes in the gut and liver

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37
Q

What is distribution?

A

Occur after a drug has been absorbed, where the drug is distributed to the tissues.

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38
Q

When is a drug active?

A

When a drug leaves the bloodstream and enter the intercellular spaces.

When it is unbound from the proteins in the plasma.

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39
Q

Is distribution reversible?

A

Yes, drugs can diffuse from the intercellular spaces back to the bloodstream

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40
Q

What do drugs bind to in order to enter tissues?

A

Proteins in the plasma

Example - albumin or alpha1-glycoprotein

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41
Q

When is a drug inactive?

A

When in the bloodstream and bound to a plasma protein

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42
Q

What change the amount of drug bound to the plasma protein?

A

Renal failure

Hypalbuminaemia

Pregnancy

Other drugs

Saturability of binding

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43
Q

If a drug is 96% protein bound, what percentage of the drug is free and available for action?

A

4%

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44
Q

If the amount of unbound drug changes from 4% to 6%, then how much will the level of free drugs have increased by?

A

50%

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45
Q

What is the volume of distribution (Vd)?

A

The volume of plasma that would be necessary to account for the total amount of drug in a patient’s body, if the drug were present throughout the body at the same concentration as found in the plasma

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46
Q

What is the units for the Vd?

A

Litres per kg

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47
Q

What does a greater Vd value mean?

A

The drug has a greater ability of diffusing into and through membranes

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48
Q

What should the Vd value be/

A

42L

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49
Q

What should the Vd value if the drug stays in the extracellular fluid and cannot penetrate cells?

A

12L

50
Q

What should the Vd value be If the drug is highly protein bound?

A

3L

51
Q

What is clearance?

A

Defined as the theoretical volume from which a drug is completely removed of a period of time.

Measure of elimination

52
Q

What is the units of clearance?

A

ml/min

53
Q

What does renal clearance depend upon?

A

Concentration and urine flow rate

54
Q

What does hepatic clearance depend upon?

A

Metabolism and billiard excretion

55
Q

What is the half-life (t1/2)?

A

The time taken for the drug concentration in the blood to decline to half of the current value

56
Q

What is half life dependent upon?

A

The volume of distribution

Rate of clearance

57
Q

What happens if the half-life is prolonged? Why?

A

Toxicity of drug will increase.

Reduced clearance of the drug and large volume distribution.

58
Q

How do we achieve a steady state concentration of a drug?

A

A loading dose, which is an initial higher dose to a drug which may be given at the beginning of a course before dropping down to a lower maintenance dose.

59
Q

What is drug elimination?

A

The removal of an active drug and metabolites from the body

Determines the length of action of the drug

60
Q

What is drug elimination dependent upon?

A

Body metabolism (occurs in liver)

Drug excretion (occurs in kidney)

61
Q

What is drug excretion dependent upon?

A

Glomerular filtration

Passive tubular reabsorption

Active tubular reabsorption

62
Q

What is glomerular filtration?

A

Process whereby a clear fluid is produced from the blood perfusing the glomerulus at the beginning of each nephron

All unbound drugs will be filtered at the glomerulus as long as their molecular size, charge or shape are not excessively large.

63
Q

What is active tubular secretion?

A

When drugs are actively secreted into the proximal tube, within the nephron in the kidneys.

The molecules secreted are acidic and basic compounds as well as protein bound drugs

64
Q

What is passive tubular secretion?

A

As the filtrate moves from the proximal tubule, any drugs present is concentrated.

Passive diffusion along the concentration gradient allow the drug to move back through the tubule into circulation.

Only un-ionised drugs are reabsorbed.

Affected by renal failure

65
Q

Apart from the kidneys, what else is involved in excretion?

A

The biliary system

Drugs may be passively or actively secreted not the bile. Many drugs are then reabsorbed from the bile into the circulation. This is called enter-hepatic circulation. It continues until the drugs is metabolised in the liver or excreted by the kidneys.

66
Q

What can metabolism of a drug in the liver lead to?

A

Conjugation of the drug, which means that is cannot be reabsorbed from the intestine

67
Q

What is drug metabolism?

A

The biochemical modification of pharmaceutical substances by living organisms usually through the action of enzymes

Converts lipid soluble, non-polar compounds to lipid soluble, polar compounds so that they can be excreted - as only polar compounds can undergo excretion.

68
Q

Where does metabolism take place?

A

Liver, Gi tract, kidneys and lungs - but mainly liver

69
Q

What is the purpose of metabolism?

A

To increase water solubility of drugs to aid excretion

Deactivate compounds

70
Q

What are prodrugs?

A

Drugs which are activated by metabolism.

The inactive form of prodrugs is absorbed into the bloodstream and during metabolism it is converted into tis active form

71
Q

What is phase I of metabolism?

A

Converts drug into a more reactive species

Takes place through three reactions; oxidation, reduction and hydrolysis. These reactions result in the polar groups of drug molecules being exposed or introduced, thus increasing the polarity of the compound and providing an active site for phase II metabolism

72
Q

What enzymes are involved in phase I of metabolism?

A

Cytochrome P-450 enzymes

73
Q

What is the CYP3A4 enzyme?

A

Enzyme in the liver and gut, metabolises a wide range of drugs

Responsible for the pre-systemic metabolism of several drugs, which is when the drug is metabolised before it reaches the systemic circulation

74
Q

What is the CYP2D6 enzyme?

A

Metabolises anti-depressents, antipsychotics and the conversion of codeine to morphine.

75
Q

What is the CYP1A2 enzyme?

A

Enzyme induced by smoking and is important in the metabolism of theopylline

Therefore, smokers require a higher dose of theophylline a as they excrete it much quicker

76
Q

What is phase II of metabolism?

A

Involves conjugation of the drug, which increases the water solubility of the drug and therefore its excretion.

Usually inactivates the drug

77
Q

What factors affect metabolism?

A

Other drugs

Genetics

Hepatic blood flow

Liver disease

Age

Sex

Ethnicity

Pregnancy

Enzyme Induction

Enzyme Inhibition

78
Q

How can genetics affect metabolism rates?

A

An individual may inherit a set of genes that slow or increase metabolism rates.

Gene mutations can also occur that result in deficiencies or absence of a particular metabolising enzyme, which can increase drug toxicity or enhanced metabolism

79
Q

How does age affect metabolism rates?

A

Drug metabolising enzymes are often found deficient or reduced in the foetus or premature infant. Renal function is also deficient, which means that drug and metabolites can rapidly build up to toxic levels as excretion isn’t occurring as regularly.

80
Q

How does race affect metabolism rates?

A

Racial differences in the genetic expression of cytochrome P-450 isoforms

81
Q

How does pregnancy affect metabolism rates?

A

A female’s enzyme activity increases which means that they metabolise medicines more rapidly.

Hormonal changes can also effect drug metabolism

82
Q

What is enzyme induction?

A

Increased synthesis and activity of a drug.

83
Q

How can enzyme induction affect drug metabolism?

A

Increased synthesis and activity of a metabolising-drug, which decreases the drug effect

84
Q

How can enzyme inhibitor affect drug metabolism?

A

Decreased activity of drugs, which increases the drug effect

85
Q

Name the four ways that drugs can be delivered

A

Oral

Injection

Transdermal

Carrier based

86
Q

What are carried based drug delivery systems?

A

A drug carrier is any substrates used in the process of drug delivery

They are used to improve bioavailability, effectiveness and safety of drugs

87
Q

Name two common drug carriers

A

Monoclonal antibodies

Liposomes

88
Q

What is the rate limiting step of tablets ?

A

Dissoloution, break down of the tablets

89
Q

Why are some tablets coated?

A

In order to delay disintegration of the tablet until it reaches the small intestine

Prevent it from being broken down in the stomach by acid.

Allows the stomach to be protected from the drug

90
Q

What are modified release tablets?

A

Prolong the release of the drug as they are related at a slower rate and contain more of the active drug

Allow the drugs to be maintained within the threapetuic range

Need for frequent dosing reduced, patients are more compliant with taking medication

91
Q

What are the advantages of prodrugs?

A

Prolongation of duration of action

Avoidance of degradation in the gut

92
Q

What are suspensions?

A

Dispersions of drug particles in a liquid phase

93
Q

What are the two types of subcutaneous injections?

A

Dermojets - mass inoculation

Pellet implantations - drug implanted under skin as a solid pellet to provide uniform systemic effects

94
Q

What are suppositories?

A

Small objects that you put in the rectum, once inside it melts and releases the drug

95
Q

What are adverse drug reactions?

A

Any response to a drug which is unintended

96
Q

What are acute ADRs?

A

When bronchiconstriction occurs within 60 minutes of the drug administration

97
Q

What are sub-acute ADRs?

A

When a rash and serum sickness occurs within 24 hrs of drug delivery

98
Q

What are latent ADRs?

A

When eczematous eruptions occur after two days of drug delivery

99
Q

What are mild ADRs?

A

When the ADR is bothersome but requires no change in therapy

100
Q

What are moderate ADRs?

A

When the ADR results in a change in therapy, additional treatment and hospitalisation

101
Q

What are severe ADRs?

A

When an ADR becomes life-threatening

102
Q

What are type A ADRs?

A

When ADR is due to a high dose and the response is normal but augmented

Reactions are reversible as we can reduce or stop drug delivery

Not life-threatening

103
Q

What are the two types of type A ADRs?

A

Augmentation of the primary effect

Augmentation of the secondary effect

104
Q

What are type B ADRs?

A

When ADR reaction is bizarre.

They cause serious illness or death

Unrelated to dose

Cannot be reversed

Can be caused be genetics or drug allergies

105
Q

What are type C ADRs?

A

When ADR is related to the duration of treatment and dose.

106
Q

What are type D ADRs?

A

When ADR occur a long time after treatment.

These effects include teratogenesis or carcinogenic

107
Q

What is teratogenesis?

A

Process by which congenital malformations are produced in an embryo or foetus.

Caused by mothers treated with the drug isotretinonin during the first trimester of pregnancy

Drug is therefore avoided during pregnancy

108
Q

What are type E ADRs?

A

When ADR occurs when a drug treatment is stopped suddenly following long term use.

To prevent these reactions, we can ease the dose of the drug over a long period of time

Can cause death

109
Q

What are type F ADRs?

A

When ADR is due to a failure of therapy or drug interactions.

They are dose related

110
Q

What makes individuals more susceptible to ADRs?

A

Age - children and elderly more susceptible

Multiple medications - leads to more drug interactions

Multiple co-morbid conditions - patient on more drugs

Inappropriate prescribing

Genetics

Sex - more common in females

111
Q

Where can we report ADRs?

A

Yellow card scheme

112
Q

What is a drug interaction?

A

When the pharmacological effect of two or more drugs given together is not just a direct function of their individual effects

113
Q

What is an object drug?

A

A drug whose activity is affected by a drug interaction

114
Q

What is a precipitant?

A

The agent which precipitates a drug interaction

115
Q

What drugs are susceptible to interactions?

A

Those with a narrow therapeutic index, which means that a small change in blood levels can induce profound toxicity

Therefore, we monitor these drugs

116
Q

What patients are susceptible to drug interactions?

A

Those who take a high number of medications

Elderly and young

Those who are undergoing complicated procedures and have multiple prescribing conditions

Those with chronic conditions

117
Q

What are pharmacodynamic drug interactions?

A

When the pharmacodynamic actions of a drug are changed due to the presence of another drug either acting directly on the same receptor or indirectly on different receptors

118
Q

What effects can pharmacodynamic drug interactions have?

A

Antagonistic - effect of two drugs is actually less than the sum of the effect of the two drugs taken separately

Additive - effect of two drugs is the same as the sum of the effect of the two drugs taken separately

Synergistic - effect of two drugs is actually less than the sum of the effect of the two drugs taken separately. This is because the two drugs have the same pharmacological effect and are acting on the same receptor at the same time

119
Q

What are pharmacokinetic drug interactions?

A

Due to one drug altering the ADME of another drug.

A - absorption can be altered by the formation of insoluble complexes, altered pH, altered bacterial flora or altered GI motility.

D - distribution can be altered by protein-protein displacement or protein-binding displacement.

M - metabolism altered when drugs inhibition’s the cytochrome system or induce the cytochrome system

E - excretion altered by changes in GFR and tubular secretion

120
Q

What is protein-binding displacement?

A

Occurs when there is a reduction in the extent of plasma protein binding of a drug caused by the presence of another drug.

Results in increased bioavailability of the displaced drug, which is now pharmacologically active.

Two main proteins - albumin and alpha1-glycoprotein.

121
Q

How do we deal with a drug interaction?

A

Alter dose timing

Alter dose

Monitor drug level

Year One - Principles of Disease (15 decks)

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