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Formulations (3rd Year) > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

Describe the process of drugs being taken orally to entering the bloodstream.

A

Disintegration, dissolution, small intestine, liver, bloodstream.

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2
Q

What does the symbol ‘ka’ denote?

A

The absorption rate constant.

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3
Q

What is the symbol used to show the absorption rate constant?

A

Ka.

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4
Q

What does the term ‘F’ denote?

A

Oral Bioavailability.

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5
Q

What symbol is used to show oral bioavailability?

A

F.

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6
Q

What route of administration excludes the absorption step?

A

Intravenous.

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7
Q

What routes of administration include the absorption step?

A

Oral, topical, SC, IM, inhalation.

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8
Q

What is the ideal molecular weight for absorption?

A

<500.

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9
Q

How can pH affect drug absorption?

A

Changes in pH in the intestines and the blood change the ionization states of drugs in each area. Ionized drugs have a harder time passing from the intestines to the blood. Non-ionized drugs can pass from the intestines to the blood easier. Hence, ionized drugs have a slower absorption rate.

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10
Q

What are the pH of the stomach and intestinal fluids?

A

1.2.

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11
Q

What is the pH of the blood?

A

7.4.

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12
Q

How does a weakly acidic drug exist in the intestinal fluid and the blood respectively?

A

It will exist in its unionized form in the intestinal fluid. It will exist in the ionized form in the blood.

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13
Q

How does a weakly basic drug exist in the intestinal fluid and the blood respectively?

A

It will exist in its ionized form in the intestinal fluid. It will exist in its unionized form in the blood.

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14
Q

How does salt formation affect the absorption of drugs?

A

Salt formation can increase the solubility of weakly soluble drugs. Increased solubility leads to increased absorption.

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15
Q

How is lipophilicity measured?

A

LogP.

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16
Q

How does lipophilicity affect drug absorption?

A

The greater the lipophilicity of the drug, the greater the absorption of the drug. This is because the barrier for absorption is also lipophilic.

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17
Q

List the 4 drug absorption pathways.

A

Paracellular, transcellular, cerrier mediated, endocytosis.

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18
Q

Describe the paracellular drug absorption pathway.

A

Drug molecules pass through gaps between cells. Molecules must be of a small molecular weight.

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19
Q

Describe the transcellular drug absorption pathway.

A

A passive process where the drug passes from one side of the cell to the other. Drug molecule must be lipophilic.

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20
Q

Describe the carrier-mediated drug absorption pathway.

A

The drug molecule is transported by active carrier proteins that require ATP.

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21
Q

Describe the endocytosis drug absorption pathway.

A

Drug molecules are taken up in vesicles to be passed across the cell.

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22
Q

Is the blood flow in the brain, liver, kidneys, and heart fast or slow?

A

Fast.

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23
Q

Is the blood flow in the bones, muscles, and skin fast or slow?

A

Slow.

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24
Q

What is the volume of distribution?

A

The theoretical volume which helps you to convert the dose of drug into its systematic plasma concentration.

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25
Q

What symbol is used to denote the volume of distribution?

A

Vd.

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26
Q

What does the symbol ‘Vd’ denote?

A

The volume of distribution.

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27
Q

If the volume of distribution is high, what does this mean?

A

That the drug is concentrated in the tissues.

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28
Q

If the volume of distribution is low, what does this mean?

A

That the drug is concentrated in the blood.

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29
Q

What are the two main plasma proteins involved in drug binding?

A

Albumin and alpha-1 acidic glycoprotein.

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30
Q

What drugs do albumin bind?

A

Acidic and neutral drugs.

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31
Q

What drugs do alpha-1 acidic glycoprotein bind?

A

Basic drugs.

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32
Q

How does high protein binding affect the distribution of drugs?

A

Highly protein bound drugs will take a longer time to reach their intended site of action. They will also have a longer action.

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33
Q

Where does drug metabolism typically occur?

A

The liver.

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34
Q

Name the group of enzymes that are responsible for drug metabolism.

A

Cytochrome P450.

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35
Q

What is believed to be the reason humans (and other organisms) have evolved cytochrome P450 enzymes?

A

To defend the body from ingested toxins.

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36
Q

What percentage of drugs on the market are metabolised by Cytochrome P450 enzymes?

A

60%.

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37
Q

What does a high metabolism and excretion mean for the dosage regimen of the drug?

A

More doses must be given daily.

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38
Q

What does a low metabolism and excretion mean for the dosage regimen of the drug?

A

Fewer doses can be given per day.

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39
Q

Through what means can drugs be excreted from the body?

A

Urine (kidneys), faeces (liver, small intestine), sweat, tears, hair, lungs.

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40
Q

Excretion through which route is the primary route used when a breathalyzer test is administered?

A

The lungs.

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41
Q

Define clearance.

A

The volume of blood or fluid from which drug is completely removed per unit time.

42
Q

What two clearance measurements is total clearance (CL Total) made up of?

A

CL hepatic and CL renal.

43
Q

Clinically, how can information on blood concentrations be gained?

A

By sampling blood levels over time.

44
Q

If one had no capacity for drug clearance, what would be the outcome?

A

Build up of drug and metabolites, leading to toxicity and death.

45
Q

What can concentration vs time graphs show us?

A

How long absorption takes, how long distribution takes, how effective elimination is, how long is the duration of action, is the drug toxic (MTC), how can one maintain the duration of action.

46
Q

What is an IV bolus dose?

A

An IV bolus dose is a direct injection of a full dose of drug into systematic circulation.

47
Q

What is the bioavailability of an IV bolus dose?

A

100%.

48
Q

What order kinetics does the pharmacokinetics of an IV bolus dose follow?

A

First order.

49
Q

On a concentration vs time graph for an IV bolus dose, what does the intercept represent?

A

The starting dose.

50
Q

On a concentration vs time graph for an IV bolus dose, what does the gradient of the line represent?

A

The rate of elimination.

51
Q

Once the gradient and intercept of a concentration vs time graph are established, what other parameters can be determined?

A

Half-life, clearance, the volume of distribution.

52
Q

What does a shorter half-life suggest?

A

The drug has a faster clearance.

53
Q

Define an IV infusion.

A

The slow pushing of a drug into the blood over a set time.

54
Q

Why are IV infusions prefered over an IV bolus dose?

A

They are more appropriate when repeated doses are required or when the drug concentration must be kept constant. IV infusions are used in a hospital to maintain a constant level of therapy in an individual. IV infusions can also be stopped if there are adverse drug reactions with fewer negative results compared to an IV bolus dose.

55
Q

Define steady state.

A

The balance between the infusion of drug in and the clearance f drug out. Maintaining a plasma concentration.

56
Q

How long, in half-lives, does it take for steady state to be reached for a drug?

A

4 to 5 half-lives.

57
Q

A drug with a long half-life will take an unacceptably long time to reach steady state concentration. In many clinical settings, we require a rapid clinical onset. How can this be achieved?

A

By starting the patient with a loading dose to artificially reach steady state concentration.

58
Q

What is the same as when an IV infusion is stopped?

A

Giving an IV bolus dose.

59
Q

What does the area under the curve (AUC) represent?

A

The residency of the drug in the body and is used to calculate the bioavailability (F). It is also very useful in calculating the clearance of the drug.

60
Q

How can the area under the curve (AUC) be calculated?

A

AUC = dose/clearance.

61
Q

Within what margins should the bioavailability of generic drug be, compared to the innovator?

A

within 10-15%.

62
Q

How does the volume of distribution differ for an overweight patient?

A

Their volume of distribution will be higher.

63
Q

How does the volume of distribution differ for an underweight patient?

A

Their volume of distribution will be lower.

64
Q

How can the dosage regimen be changed to provide an adequate therapeutic effect for an overweight patient? Why is this necessary?

A

The dose must be increased. This is because the volume of distribution is greater so more drug is needed to reach the target area.

65
Q

How can the dosage regimen be changed to provide an adequate therapeutic effect for an underweight patient? Why is this necessary?

A

The dose must be decreased. This is because the volume of distribution is lower so less drug is needed to reach the target area.

66
Q

Using different formulations can affect the shape of the concentration vs time graph. If all other parameters are maintained the same, what portion of the concentration vs time graph will change when the formulation is changed?

A

The rate of change of the ascending limb.

67
Q

In terms of pharmacokinetics, what can diseases of the liver and kidneys change?

A

The rate of elimination of the drug.

68
Q

What does a reduction in the production of plasma proteins do to the metabolism?

A

The extent of metabolism is increased.

69
Q

How is the metabolism of drugs affected by a reduction in blood flow to the liver?

A

The metabolism is reduced as less drug is brought to be acted upon by the enzymes.

70
Q

As well as the liver, where else are CYP450 enzymes found hence drug metabolism also occurs?

A

The small intestine.

71
Q

How many main groups are CYP450 enzymes split into? How many sub-classes are there?

A
  1. Split into classes A-E.
72
Q

CYP2D6 makes up 2% of all CYP450 enzymes however metabolises what percentage of drugs? Especially what type of drug?

A

25% of all drugs, especially basic drugs.

73
Q

What drugs show non-linear kinetics?

A

Phenytoin and carbamazepine.

74
Q

What can inhibitory drug-drug interactions lead to?

A

Reduced metabolism, increased plasma concentration, AUC increases, elimination rate increases, increased Cmax.

75
Q

Define clearance.

A

The rate at which the liver eliminates drugs from the body.

76
Q

What is the maximum liver blood flow?

A

1500ml/min.

77
Q

How is hepatic clearance (CL H) calculated?

A

CL H = hepatic blood flow (Q) x Extraction ratio (E)

78
Q

What effect does an age-related reduction in cardiac output have on drug metabolism?

A

Reduced liver blood flow leading to reduced metabolism.

79
Q

What effect does age-related reduced hepatic function have on drug metabolism?

A

Reduced enzymes leading to reduced metabolism.

80
Q

Describe cirrhosis.

A

Permanent loss of liver cells. Different levels of cirrhosis lead to different levels of dose adjustment.

81
Q

Describe hepatitis.

A

Inflammation of the liver. If mild it is nothing significant. If it is major it will require dose adjustments.

82
Q

What 5 laboratory tests are used to generate the Child-Pugh score for liver function?

A

Serum albumin, total bilirubin, prothrombin time, ascites, hepatic encephalopathy.

83
Q

When are genetic differences in drug metabolism often first seen?

A

When the drug enters the market and has been subjected to the wider population.

84
Q

Metabolism of which drugs are affected by polymorphisms in the enzyme CYP2B6?

A

Doxorubicin, Nicotine.

85
Q

Metabolism of which drugs are affected by polymorphisms in the enzyme CYP2C9?

A

Warfarin, doxorubicin.

86
Q

Metabolism of which drugs are affected by polymorphisms in the enzyme CYP2C19?

A

Benzodiazepines, PPIs.

87
Q

Metabolism of which drugs are affected by polymorphisms in the enzyme CYP2D6?

A

Beta-blockers, anti-depressants, codeine.

88
Q

Metabolism of which drugs are affected by polymorphisms in the enzyme CYP3A4?

A

Erythromycin, HIV protease inhibitors.

89
Q

How is a person with two normal alleles for a specific CYP enzyme described? Describe their metabolism?

A

They are described as an extensive metaboliser. Their metabolism is normal.

90
Q

How is a person with one normal allele for a specific CYP enzyme described? Describe their metabolism?

A

They are described as an intermediate metabolizer. Their metabolism is decreased.

91
Q

How is a person with two poorly functioning alleles for a specific CYP enzyme described? Describe their metabolism?

A

They are described as a poor metaboliser. Their metabolism is close to none.

92
Q

How is a person with one normal and one overactive allele for a specific CYP enzyme described? Describe their metabolism?

A

They are described as an ultrarapid metaboliser. Their metabolism is increased.

93
Q

SNPs in which CYP enzyme are less prominent in Chinese/Japanese subjects compared to Caucasian subjects?

A

CYP2D6.

94
Q

SNPs in which CYP enzyme are more prominent in Chinese/Japenese subjects compared to Caucasian subjects?

A

CYP2C19.

95
Q

How many SNPs have been found for the CYP that metabolises Warfarin; CYP2C9? How many reduce metabolism?

A

3 SNPs. 2 reduce metabolism.

96
Q

What is the prevalence of CYP2C9 SNPs in Caucasians?

A

8-15%.

97
Q

What is the prevalence of CYP2C9 SNPs in Chinese populations?

A

80%.

98
Q

How many SNPs have been found for the CYP enzyme that metabolises Clopidogrel; CYP2C19?

A

3.

99
Q

As well as drugs, what other products can interact with drugs?

A

Food (milk, grapefruit), Herbals (SJW), Lifestyle (smoking, drinking).

100
Q

Patients of which groups are more susceptible to drug interactions?

A

Pregnant women, geriatric patients, patients suffering from renal or hepatic failure.

101
Q

Describe beneficial drug interactions.

A

Interactions that can potentiate the actions of one or more drugs. They can also be beneficial antagonistically.

102
Q

What can undesirable drug interactions lead to?

A

Toxicity and loss of efficacy.

Formulations (3rd Year) (2 decks)

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