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5 - Pharmacology > Pharmacokinetics and oharmacodynamics > Flashcards

Pharmacokinetics and oharmacodynamics Flashcards

1
Q

Define pharmacokinetics

A

Study of what the body does to the drug

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2
Q

Define pharmacodynamics

A

Study of what the drug does to the body

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3
Q

Define pharmacogenetics

A

The effects of genetic variability on the pharmacokintics or dynamics of a drug on an individual

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4
Q

What are the four main mechanisms involved in pharmacokinetics?

A

AbsorptionDistributionMetabolismElimination

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5
Q

Define systemic entry

A

Entry of a substance so that the whole body is affected

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6
Q

What can systemic entry of drugs be affected by?

A
  • GI motility- Splanchnic blood flow (blood flow to visceral organs)- Molecular size- pH levels- Presence of active transport systems
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7
Q

Define first pass metabolism

A

Any metabolism that occurs before the drug enters the systemic circulation.

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8
Q

Where can first pass metabolism occur?

A
  1. Liver and portal venous system2. Within the gut lumen (gastric acid, proteolytic enzymes)3. In the gut wall (P-glycoprotein efflux transports drugs back into the lumen from the intestinal enterocyte)
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9
Q

Define bioavailability

A

The amount of drug which enters the systemic circulation in an unchanged form, relative to that is administered via IV.

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10
Q

How can you calculate bioavailability?

A

Amount of drug reaching systemic circulation / total amount of the drug administered

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11
Q

What is bioavailability affected by?

A
  • Intestinal motility- Food (lipid-soluble or water-soluble)- Age- First-pass metabolism. - Vomiting/malabsorption- Drug formulation
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12
Q

Define drug distribution

A

The ability of a drug to “dissolve” in the body

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13
Q

What are the two main factors that affect the distribution of a drug?

A

LipophilicityProtein binding

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14
Q

How does lipophilicty affects a drug’s distribution?

A

The more lipophillic a drug is, the more likely it will mvoe from the blood to tissues with a higher lipid content

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15
Q

Describe where you mainly find lipid-insoluble drugs

A

Are mainly confined to the plasma and interstitial fluid

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16
Q

Describe where you would mostly find lipid soluble drugs

A

Are able to reach all the body compartments and will accumulate in fat

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17
Q

How does protein binding affect the distribution of a drug?

A

A drug must be in an unbound states in order for it to be able to interact with receptors.

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18
Q

Give some proteins that bind drugs and which kind of drugs d they bind to

A

Albumin - acidic drugsGlobulins - hormonesLipoproteins - basic drugsAcid glycoproteins - basic drugs

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19
Q

Define an object drug

A

The number of molecules administrated which are lower than the number of binding sites

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20
Q

Define a precipitant drug

A

The number of molecules administered are higher than the number of binding sites

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21
Q

Give an example of an object drug

A

Warfarin

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22
Q

Give some examples of precipitant drugs

A

PhenytoinAspirinSulphonamides

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23
Q

What effects do object and precipitant drugs have on each other?

A

Precipitant drugs will displace the binding of an object drug.

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24
Q

What can cause changes to protein binding?

A
  • hypoalbuminaemia- pregnancy- renal failure- displacement by other drugs
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25
Q

When can the displacement of other drugs be an issue?

A

Where there is:- high proteins binding- Low vol of distribution- a narrow therapeutic ratio

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26
Q

What compartments make up the extracellular fluid of the body?

A

PlasmaInterstitial fluidTranscellular fluidFat

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27
Q

Define the volume of distribution

A

A measure to see how well a drug distributes throughout the body systems

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28
Q

How do you measure the volume of distribution?

A

Total amount of drug in the body / concentration of the drug in the plasma

29
Q

When would you have a high volume of distribution?

A

When the drug is able to move through a large number of the bod compartments

30
Q

When would you have a low volume of distribution?

A

When the drug is confined to one body compartment and cannot travel to others.

31
Q

Give the Vd of a drug which is confined to the plasma

A

around 0.1l.kg-1 or less than 5 litres

32
Q

Give the Vd of a drug which is confined to the extracellular fluid

A

around 0.4l.kg-1 or less than 15 litres

33
Q

Give the Vd of a drug which is able to travel throughout the body compartments

A

greater than 1l.kg-1 or more than 15 litres

34
Q

What can tissue distribution be affected by?

A

Lipid solubilityProtein bindingDisease statesRegional blood flowSpecific receptor sites in tissuesDrug interactions

35
Q

Define drug metabolism

A

The enzymatic conversion of one chemical entity to another within the body. It is made up of two phases.

36
Q

Define Phase 1 reactions

A

Catabolic. Involves producing products which are chemically reactive. Allows for drugs to be conjugated.

37
Q

Define Phase 2 reactions

A

Anabolic and involve conjugation. This produces inactive products.

38
Q

Where do the phase 1 and phase 2 reactions occur?

A

In the liver

39
Q

Give some characteristics of phase 1 reactions

A

Are dependent on cytochrome P450 enzymes and NADPH

40
Q

What is happening when you calculate a volume of distribution which is greater tan the body weight of the patient?

A

Tissue binding is occurring- the drug is accumulating in the circulation- usually very lipophillic drugs which are binding to adipose tissue

41
Q

Give two characteristics of CYP450 and NADPH

A

Can be induced and inhibited. Often by other drugs of chemicals.

42
Q

Give some drugs that induce CYP450

A

PhenytoinCarbamezepineBarbituatesRifampicinAlcohol (chronic)Sulphonureas and St Johns WortPC BRAS

43
Q

Give some drugs the inhibit CYP450

A

Grapefruit juiceOmeprazoleDisulframErythromycinValroateIsonazidCimetidine ane CiprofloxacinEthanol (acutely)Sulphonamides

44
Q

What happens in phase 2 metabolism?

A

The reactive intermediate is conjugated with a polar molecule to form a water soluble complex by conjugation

45
Q

What are some common conjugates?

A

Glucoronic acidSulphonamidesGlutathione

46
Q

What is needed in order for phase 2 reactions to occur?

A

Specific enzymes and Uridine Diphosphate Glucuronic Acid (UDPGA)

47
Q

Why do drugs undergo phase 2 metabolism?

A

Makes them water soluble and less lipid soluble, so that the drug can be excreted by via the kidneys in the urine.

48
Q

Give some routes by which drugs can be excreted

A

KidneyLungBreast milkSweatTearsGenital secretionsBileSaliva

49
Q

What three components determine the rate of renal excretion of a drug?

A

GFRPassive tubular resorptionActive tubular secretion

50
Q

Define Clearance

A

Is a measure of both hepatic clearance and renal clearance

51
Q

What causes a decrease in renal clearance?

A

GFR which has the effect os increasing the half life of the drug

52
Q

By what mechanism are drugs transported into urine?

A

There are organic anion and cation transporters which are renal transporters to actively transport drugs from the plasma into the lumen of the nephron

53
Q

Where do you find organic anion and cation transporters?

A

In the proximal convoluted tubule and have parallels with CYP450s as they are able to transport a wide range of molecules

54
Q

What factors affect clearance?

A

Heart - affects blood flow to main elimination organsRenal Hepatic

55
Q

Define half life

A

The amount of time taken for a drug to reach half the concentration which it had been when measured.

56
Q

What factors affect half life?

A

HeartRenalHepatic

57
Q

How can you calculate half life?

A

(0.693 x Vd) / clearance

58
Q

Define 1st order kinetics

A

The rate of elimination if proportional to drug level. A constant fraction is eliminated in unit time and you are able to define a half life.

59
Q

What kind of curve do you get with 1st order kinetics?

A

Linear curve- against a logarithmic scale

60
Q

Define zero order kinetics

A

The rate of elimination is constant and you cannot define a half life. Drug monitoring is ESSENTIAL

61
Q

What type of curve do you get with zero order kinetics?

A

A straight line curve- the half life decreases with decreasing concentration

62
Q

What differences do you get the elimination kinetics with varying concetrations of that drug?

A

At therapetic levels - linear kinetics are seen as the CYPs and liver are able to deal with the drug effectively. At higher levels - elimination will become saturated and show zero order kinetics

63
Q

Give some drugs which show saturated kinetics on overdose

A

AspirinPhenytoinVerapamilFluoxetine

64
Q

Which drugs are more likely to result in toxicity?

A

Zero order drugsDrugs which have:- long half life- narrow therapeutic window- drugs likely to have drug:drug interactions

65
Q

Define therapeutic window

A

The concentration within which a drug has a therapeutic effect without giving unacceptable adverse effects

66
Q

Define steady state concentration

A

The concentration at which elimination and administration are equal and the drug concentration stays within set values

67
Q

How long does it take to reach a steady state?

A

4-5 half lives

68
Q

What occurs when you want to reach the steady state quickly?

A

You will give a loading does so that you are able to reach the steady state and therapeutic window quickly.

69
Q

Define Cmax

A

The maximum concentration of a drug

5 - Pharmacology (17 decks)

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