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Pharmacology > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is pharmacokinetics?

A

Effect of the body on drug delivery to site of action

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2
Q

4 key processes of pharmacokinetics?

A

Absorption,distribution,metabolism and excretion

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3
Q

What is absorption?

A

Processed that take place between site of administration and site of measurement

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4
Q

3 methods of drug absorption?

A

Membrane pores
Membrane diffusion
Carrier mediated

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5
Q

What can use membrane pores?

A

Drugs with low molecular weight or small ions

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6
Q

What drugs can diffuse through membranes?

A

Lipid soluble molecules

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7
Q

What can use carrier mediated

A

The drug must resemble natural ligand or substrare

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8
Q

What factors effect drug absorption?

A 
Lipid solubility 
Ionisation 
Formulation 
Gastrointestinal function 
First pass metabolism
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9
Q

How do you work out extent of ionisation?

A

Henderson hasselbach equation

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10
Q

What is Henderson hasselbach equation?

A

pH=pka+log [conjugate base]/[conjugate acid]

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11
Q

When do you get 50% ionisation?

A

When pH=pka

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12
Q

When are acids most ionised?

A

At high pH strong acid is below 3 ph

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13
Q

When are bases most ionised?

A

Low ph, ph higher than 10 for strong base

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14
Q

How does gastrointestinal function effect absorption?

A

gastric emptying effects time for absorption to occur

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15
Q

What is first pass metabolism?

A

Drugs administered orally absorbed in gastrointestinal tract then transported by portal vein to the liver where it’s metabolised

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16
Q

What is bioavailability?

A

Fraction of dose passing from site of administration into general circulation

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17
Q

What is the intravenous bioavailability?

A

1

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18
Q

Reasons for low bioavailability?

A

Tablet not fully dissolved
Decomposition on gut lumen
Due to first pass metabolism

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19
Q

How do you work out bioavailability?

A

Need 2 graphs one for intravenous and one for oral. Under the graph AUC area under curve is the total amount of drug absorbed. Then divide the he oral by the i.v.

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20
Q

Bioavailability equation?

A

F=AUC(oral)/

AUC(I.v)

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21
Q

Name routes of drug administration?

A

Oral,intravenous,subcutaneous,intramuscular,inhalation,transdermal and nasal

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22
Q

What is distribution in pharmacokinetics?

A

Rate/extent if parent drug entering tissue and it’s elimination afterwards

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23
Q

What is the blood brain barrier BBB?

A

Homeostatic mechanism allowing a constant CNS environment

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24
Q

How is BBB made?

A

It’s made of endothelial cells held together by tight junctions

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25
Q

How do you transport across BBB?

A

Many active transporters -in (nutrients) -out (waste)

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26
Q

What area of the brain has no BBB?

A

Area postrema

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27
Q

What is meant by the area postrema is an emetic centre?

A

It causes you to be sick (emesis)

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28
Q

Lipid soluble drug entry to the brain is…

A

Fast and high concentration

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29
Q

Water soluble drug entry to the brain is…

A

Struggles to enter and can’t get high concentrations

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30
Q

How is Parkinson’s disease caused?

A

Caused by reduced dopamine in the substantia nigra leading to reduction in dopaminergic activity in the nigrostratial pathway

31
Q

What is the problem with Parkinson’s treatment?

A

Dopamine can’t enter the brain due to being a polar molecule and the BBB

32
Q

How can you overcome the BBB with dopamine?

A

Produce a precursor to dopamine, it’s called levadopa

33
Q

How does levadopa work?

A

Levadopa enters the brain via amino acid transporters through the BBB due to extra amine group. Then dopa-decarboxylase converts levadopa to dopamine

34
Q

Problems with levadopa?

A

Dopa-decarboxylase is in the whole body so large doses are need leading to accumulation and side effects

35
Q

How do we prevent negative effects of levadopa?

A

Use drug carbidopa which inhibits dopa-decarboxylase but is opolar so can’t cross BBB so levadopa can only become dopamine in the brain

36
Q

What factors effect distribution of a drug?

A

Rate of diffusion
Plasma protein binding
Tissue composition

37
Q

What is elimination in pharmacokinetics?

A

Removal of drug from the body

38
Q

How is drug eliminated from the body?

A

Metabolism and excretion

39
Q

How does metabolism remove a drug from the body?

A

Drug is transformed into a new molecule

40
Q

How does excretion eliminate drug from the body?

A

Drug expelled in liquid solid or gaseous state

41
Q

What does metabolism do to lipid soluble molecules to help them be eliminated?

A

Converts them to water soluble as they are much more easy to eliminate than lipid soluble

42
Q

Phases of drug metabolism:

A

Phase 1: oxidation,reduction,hydrolysis to introduce new functional group
Phase 2: conjugation reaction (forms covalent bond to phase 1)

43
Q

Drug metabolism is a major source of patient to patient differences in magnitude and response. Why?

A

This can be due to age, gender ,ethnic origin and disease. Half life not affected due to not occupying all enzymes

44
Q

Phase 2 conjugation reactions?

A

Examples: glucuronidation, sulphation and acetylation

45
Q

How does glucuronidation work?

A

Glucuronic acid replace hydrogen on drug, producing a water soluble product. Done by UDP-glucuronyl transferase (UDPGT).

46
Q

What is sulphation?

A

Sulphate group replaces the H in a hydroxide group to give a water soluble product. Done by sulphotransferase

47
Q

What is acetylation?

A

A mechanism used to inactivate drugs but no increase in water solubility. N-acetyl transferase. Different ethnic backgrounds have different acetylation speeds.

48
Q

Drug metabolism consequences?

A

No activity
Can have similar effects
Different pharmacological effects
Toxicological action

49
Q

Effects of being elderly on metabolism?

A

Liver size and blood perfusion decreases with age. Reducing phase 1 metabolic reactions

50
Q

Effects of being young on metabolism of drugs?

A

Drug metabolising enzymes are immature in neonatal liver so first phase metabolism is low

51
Q

What is excretion of drugs?

A

Removal of drugs from the body

52
Q

What are Routes of excretion?

A

Lungs, kidneys and Bile

53
Q

What are the 3 types of renal excretion?

A

Glomerular filtration
Ph dependent reabsorption
Renal tubular secretion

54
Q

What is glomerular filtration?

A

Small molecules filtered through 7-8nm pores, protein bound drug not filtered but some dissociates when water is reabsorbed.

55
Q

How does Ph dependent reabsorption work?

A

Lipid soluble molecules reabsorbed until they are water soluble products. Due to urine being lower pH than the plasma so the drug concentrates in fluid that make its most ionised

56
Q

How does renal tubular secretion work?

A

Active processes strip drugs from protein binding sites- many drug conjugated are substrates for active secretion

57
Q

What is biliary excretion?

A

Excretion of drugs in bile and bile salts. Usually large and conjugated drugs are eliminated.

58
Q

What is known as the extent of absorption?

A

Bioavailability

59
Q

What is apparent volume of drug?

A

Volume of plasma the dose is dissolved in ,an indication of extent of tissue uptake

60
Q

(Apparent volume of drug) V=

Two compartment distribution

A

Dose/y-intercept

61
Q

What is elimination rate?

A

Terminal rate of decrease in plasma concentration

62
Q

How do you work out elimination rate?

A

K=CL/v

63
Q

What is plasma clearance (cl)?

A

The volume of plasma cleared it a drug per a minute.

64
Q

Plasma clearance is very similar to blood perfusion. How much for liver,renal and glomerular?

A

Liver (1500ml/min)
Renal (650ml/min)
Glomerular (120-130ml/min)

65
Q

Plasma clearance= metabolic +renal clearances

A

Clearance

66
Q

Plasma clearance can be calculated from plasma concentration. How?

A

Cl=dose x F/ AUC

67
Q

How do you work out half life?

A

T1/2=0.693/k

68
Q

What is chronic administration?

A

Continuous intravenous infusion that maintains a constant concentration at site of action.

69
Q

What is the Css?

A

The point in which rate of input is at a steady and equal point with the rate of elimination

70
Q

How to work out the Css?

A

Css=rate of infusion/ clearance

71
Q

What is the loading dose?

A

The loading dose is a larger first dose.

72
Q

Why is the loading dose a larger dose?

A

To overcome the 5 1/2 half-lives it takes to reach Css as some drugs have to long half lives to be effective

73
Q

How to work out loading dose?

A

Ld=Css x V (I.v.)

Kd=Css x V/F (oral)

Pharmacology (4 decks)

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