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MEDI 202 - Genes To Community > Pharmacology > Flashcards

Pharmacology Flashcards

1
Q

What is pharmacokinetics?

A

What the body does to the drug

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2
Q

What is pharmacodynamics?

A

What the drug does to the body

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3
Q

What is the pathway of the drug?

A

Drug at the site of administration
Absorption
Distribution
Metabolism
Elimination

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4
Q

What are the routes of drug administration?

A

Intravascular (directly into the blood)
Extravascular (oral, sublingual, subcutaneous, intramuscular, rectal)
Other (inhalation, intranasal, topical, transdermal)

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5
Q

Which drugs act systematically?

A

Those given extravascularly

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6
Q

What are the advantages of giving drugs orally?

A

Easy, practical, reliable (most lily to be complied to by patients)

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7
Q

Why are most drugs absorbed in the small intestine?

A

Large surface area due to microvilli so easier absorption especially compared to stomach.

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8
Q

Where are oral drugs dissolved?

A

In the GI tract, by GI fluids, absorbed through epithelial lining and enters blood vessels

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9
Q

What happens if the time in the GI tract changes?

A

Any condition that changes the passage time of the drug in the GI tract will change the quantity of absorption

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10
Q

Which conditions change the quantity of absorption of oral drugs?

A

Diarrhea and vomiting will cause drugs to be excreted much faster, so absorption and the effect will be less.

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11
Q

What is the first-pass metabolism?

A

Some drugs may be extensively metabolised in the liver or in the intestinal mucosa before reaching the system circulation

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12
Q

What is the effect of first-pass metabolism?

A

Reduced concentration or activity of the drug

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13
Q

When a drug is absorbed in the GI tract where does it go to next?

A

Portal circulation

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14
Q

What is the sublingual method of administration usually for?

A

Usually anginatic conditions

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15
Q

What kind of drugs are taken sublingually?

A

Drugs that would be broken down by the acid of the stomach

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16
Q

What are the advantages of sublingual drugs?

A

Good absorption through capillary bed under tongue
Self-administered

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17
Q

Why do intravenous drugs have a rapid onset of action?

A

The drug is injected directly into the bloodstream, avoids GI tract and first-pass metabolism by liver

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18
Q

In which cases are intravenous drugs useful?

A

Emergencies or when patients are unconscious

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19
Q

What other administration also has a rapid onset of action? Why?

A

Inhalation Rapid delivery of drug across a large surface area of the mucous membrane of the respiratory tract and pulmonary epithelia

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20
Q

What drugs are given through inhalation?

A

Gases (aesthetics) or those dispersed in an aerosol (asthma drugs)

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21
Q

Why is the inhalation route effective?

A

Drug is delivered directly to site of action and system side effects are minimised

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22
Q

What are the advantages of rectal administration?

A

Partially bypasses the first-pass effect
Bypass destruction by stomach acid
Ideal if the drug causes vomiting

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23
Q

What are some membranes that drugs need to pass in order to reach their target?

A

Gastrointestinal mucosa (orally)
Lung mucose (inhalation)
Lymphatic or capillary walls
Cell membrane (intracellular targets)

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24
Q

How do most drugs pass across membranes?

A

Passive diffusion

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25
Q

What are some factors influencing absorption?

A

pH (unionized drugs pass more readily)
Blood flow
Total surface area
Contact time (if drug moves too fast, it cannot by absorbed)
Expression of P-glycoproteins

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26
Q

What are P-glycoproteins?

A

Transmembrane transporter protein, responsible for transporting molecules across membranes

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27
Q

What happens if there is a high expression of p-glycoproteins ?

A

Efflux pump

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28
Q

Which form of acidic drugs is unionised?

A

Protonated

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29
Q

Are protonated forms of basic drugs unionised or ionised?

A

Ionised

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30
Q

Which kind of molecules can diffuse across membrane, ionised or non?

A

Unionised, they are lipid soluble

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31
Q

Why can’t ionised molecules pass through the membrane?

A

Low lipid solubility

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32
Q

What is the Henderson - Hasselbalch equation?

A

pH = pKa + log10 (A- / HA)

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33
Q

What is the Henderson - Hasselbalch equation used for?

A

Determine the ratio of unionized to ionised
Determine degree of ionisation at specific pH

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34
Q

What does a lower pKa value indicate?

A

Stronger acid

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35
Q

If pH = pKa ?

A

pH = pKa then 50% ionised and 50% unionised

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36
Q

What happens if pH < pKa ?

A

Higher degree of ionisation for weak bases so weak acids will be absorbed more readily

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37
Q

What happens if pH > pKa?

A

Higher degree of ionisation for weak acids so weak bases would be absorbed more readily

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38
Q

What is bioavailability?

A

Extent to which administered drug reaches the system circulation intact

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39
Q

How to calculate bioavailability?

A

Compare plasma levels of drug after a particular route to levels achieved by intravenous administration of the same dose (which is 100%)

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40
Q

What are factors that are affecting bioavailability?

A

First passage elimination in the liver
Chemical stability and solubility of drug that determine extent of GI absorption

41
Q

What is bioequivalence?

A

If two drugs have comparable bioavailability and similar times to achieve peak blood concentrations.

42
Q

What is therapeutic equivalence?

A

Two drug formulations have the same dosage with the same active ingredient at the same strength and same route of administration

43
Q

What is distribution and when does it occur?

A

The process by which a drug reversibly leaves the bloodstream and enters the interstitial and the tissues. It occurs after absorption

44
Q

What are the phases of distribution?

A

Initial phase,
Delivery of drug,
Third phase

45
Q

What is the initial phase of distribution?

A

Well-perfused organs like the heart, liver, kidney, and brain receive most of the drug during the first few minutes after absorption.

46
Q

What is the second phase of distribution?

A

Delivery of drug to muscle, skin, fat, and tissues. This may take several minutes or hours before reaching steady state

47
Q

What is the third phase of distribution?

A

Drug slowly accumulates in some tissues, like fat tissue.

48
Q

What are some factors that affect drug distribution?

A

Membrane permeability
Blood flow
Plasma protein binding
pH
Capillary permeability

49
Q

What is volume of distribution?

A

The extend to which drug partitions between plasma and tissue compartments

50
Q

What does it mean is Vd is high?

A

Greater distribution to tissues

51
Q

What drugs have low Vd value?

A

Drugs that are highly bound to proteins (heparin)

52
Q

What is the equation for Volume distribution?

A

Vd = Dose/ C
C = drug concentration

53
Q

What is the effect if the drug binds to plasma proteins?

A

Slower transfer out of vascular compartment

54
Q

What are some properties of the unbound or free drug?

A

Cross membranes and undergoes distribution
Exerts pharmacological or toxicological effect
It can be eliminated from the body

55
Q

What happens when multiple drugs are taken together?

A

Drugs with greater affinity for binding can displace other drugs with lower affinity. It would also cause a rise in unbound form of drug which can change pharmaceutical effect.

56
Q

What is the elimination of a drug?

A

Irreversible removal of the drug from the body, metabolism and excretion

57
Q

What kind of drugs are metabolised?

A

Lipophilic

58
Q

What happens to the drug after metabolism?

A

Excretion, either major (urine and bile) or minor (saliva, sweat, milk, breath)

59
Q

How is the activity of the drug terminated?

A

By elimination

60
Q

What kind of drugs undergo renal excretion?

A

Small molecular weight drugs
Fully or nearly fully ionised at physiological pH
NOT protein bound

61
Q

What are the properties of most pharmacologically active molecules?

A

Lipophilic
Remain unionised or only partially ionised at physiological pH
Bound strongly to plasma proteins

62
Q

Where are lipophilic drugs eliminated?

A

In the liver

63
Q

Where are many drug metabolising enzymes found?

A

In the endoplasmic reticulum of the hepatocytes

64
Q

What happens to drugs absorbed from the GI tract?

A

Transported to the liver via portal vein

65
Q

How does the liver convert a lipophilic drug into hydrophilic water-soluble metabolites that can be excreted?

A

Biotransformation reactions by liver enzymes:
Phase I: create small polar groups in drugs via oxidation, reaction or hydrolysis reactions.

Phase II: conjugation, addition, of large polar groups such as glucuronic acid, glutathione or sulphate to small reactive groups

66
Q

What utilises phase I?

A

P450 system

67
Q

What s CYP450 and what is its function?

A

Heme-containing isozymes are located in most cells, mainly the liver and GI tract. Important for the metabolism of many endogenous compounds such as steroids and the biotransformation of exogenous substances such as drugs.

68
Q

When does phase II of metabolism take place?

A

If phase I metabolism still too lipophilic to be excreted by the kidneys.

69
Q

What happens if the substance is highly polar?

A

Rapidly excreted in urine and feces

70
Q

What are prodrugs?

A

chemicals that are converted into pharmacologically active substances by metabolic reactions

71
Q

What is an example of a prodrug?

A

Codeine is a prodrug of morphine

71
Q

What happens if active drugs are metabolised?

A

May lead to active metabolites that have longer duration of action

71
Q

What are inducers of metabolism?

A

Enhance the rate of CYP450 enzyme synthesis and or reduce enzyme degradation.

71
Q

What are the consequences of inducers of metabolism?

A

Enhance metabolism of other drugs too, may need to increase dose of affected drugs to exert desired effect

72
Q

What are inhibitors of metabolism?

A

Bind to CYP450 enzymes and therefore inhibit metabolism of other drugs

72
Q

What are the consequences of inhibitors of metabolism?

A

Reduced drug metabolism may require reduction of dose for affected drugs to avoid adverse drug reaction for effects.

73
Q

What happens to renal elimination if ionisation increases?

A

Ionised and nonionised forms are filtered, only ionised form is “trapped” in filtrate and excreted in urine

74
Q

How is nonionised form reabsorbed?

A

It passively is secreted (diffusion) in proximal tubules or distal tubules

75
Q

Which fraction of drug is filtered out by glomerulus?

A

Free, non-protein bound (unionised)

76
Q

What is the formula for excreted drug?

A

Excreted drug = Filtered + secreted - reabsorbed

77
Q

What happens if urine acidifies?

A

Increases ionisation of weakly basic drugs and increase their renal elimination

78
Q

What happens if urine alkalises?

A

Increases ionisation and elimination of weak acid drugs

79
Q

What is zero order elimination?

A

A constant amount of drug is eliminated every time
Rate is independent of drug concentration
Variable half-life

80
Q

What drugs undergo zero order elimination?

A

Ethanol, salicylates, phenytoin

80
Q

What is first order elimination?

A

A constant fraction of the drug is eliminated every time (i.e. 50%)
Rate is directly proportional to drug concentration in plasma
Constant half life

81
Q

What is the concept of clearance?

A

Volume of blood cleared of drug per unit of time

82
Q

Where does clearance mainly occur?

A

Liver and kidneys

83
Q

When is clearance constant?

A

First order kinetics

84
Q

In kidney when is clearance = GFR?

A

If there is no secretion, reabsorption, or protein binding of drug

85
Q

What is the equation for clearance?

A

CL = 0.693 x (Vd/half-life)

86
Q

Why is clearance important?

A

For determining the half life and calculating doses needed to maintain effective or therapeutic effect

87
Q

What is the elimination half-life?

A

The time for the drug concentration to reach half of its value

88
Q

What happens to the half-life if the clearance is high?

A

Shorter half-life

89
Q

What is half-life useful for?

A

Determining the time taken to reach the steady state plasma levels

90
Q

How long does it usually take to reach steady state?

A

4 to 5 half-lives

91
Q

What happens if you increase the drug infusion?

A

Concentration of drug in plasma increases but time it takes to reach steady stat is the same

92
Q

What is the goal of drug therapy?

A

Achieve and maintain concentrations within a therapeutic response while minimising toxicity and side effects

93
Q

What is the concept of a loading dose?

A

A single high dose of drug is given initially to obtain desired plasma steady state levels quickly. Followed by slower maintenance dose to maintain steady state

94
Q

What is the equation for loading dose?

A

Loading dose = (Vd) x (Desired steady state/bioavailability)

MEDI 202 - Genes To Community (23 decks)

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