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BIOM20002 - HSF > Lecture 35 - Pharmacokinetics 2 > Flashcards

Lecture 35 - Pharmacokinetics 2 Flashcards

1
Q

What type of drug is aspirin?

A

NSAID

Non-steroidal anti-inflammatory drug

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2
Q

Describe the function of aspirin in the body

A
  1. Binds covalently to COX –> inhibiting it

2. Prostoglandin synthesis halted

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3
Q

What are the effects of aspiring at the different doses?

A

50mg / day: blood thinner

350 mg / 4 hours: anti-inflammatory, analgesic

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4
Q

Describe the function of aspirin at low doses

A
  1. Acetylates COX in platelets

2. Platelets can no longer aggregate

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5
Q

What does COX normally do in platelets?

A

Makes a product that allows platelets to aggregate

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6
Q

Why can’t COX be replaced in platelets?

A

Platelets are proper cells, and they can’t make protein

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7
Q

All of an absorbed drug is subject to … on the way into the body

A

Hepatic metabolism

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8
Q

What does the liver do to drugs?

A

Inactivation
Activation
Increase solubility

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9
Q

What are the types of reactions performed by the liver on drugs?

A

Phase I:

  • modifying functional groups
  • CYPs: Cytochrome P450

Phase II:

  • conjugation (attachment of sugars)
  • increases water solubility
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10
Q

How are drugs excreted from the body?

A

Mainly kidney

Also can be secreted into bile

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11
Q

What is the functional unit of the kidney?

Describe its function

A

The nephron

Glomerulus
Bowman's capsule
PCT
Loop of Henle
DCT
Collecting Duct
Vasa recta
Afferent and efferent arterioles
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12
Q

Which processes are taking place in the nephron?

A

Filtration

Secretion

Reabsorption

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13
Q

Describe the generalised process of filtration

A

Most stuff in the glomerular blood is pushed out through the fenestrated capillaries into the Bowman’s capsule

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14
Q

Which structures maintain the integrity and function of the glomerular tuft?

A

Podocytes

  • Hold the membrane
  • Make it like a collander
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15
Q

What is the main driving force for filtration?

A

Pressure

High pressure in the glomerulus, low pressure in the Bowman’s capsule

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16
Q

How much blood is filtered per day?

A

180 L

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17
Q

What is normal blood volume in the body?

A

5 L

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18
Q

Which molecules are filtered out of the blood?

A

Ions
Sugar
Water
Amino acids

19
Q

What doesn’t get filtered?

A

Proteins

20
Q

What percentage of the blood is filtered?

A

15-20%

21
Q

Describe how structure relates to function in the PCT

A

Great SA: reabsorption

Mitochondria: active transport

22
Q

How is stuff secreted into the nascent urine

A

Through transporters:

OCT: organic cation transporter
OAT: organic anion transporter

23
Q

What is competition of secretion?

What is an example of this?

A

Penicillin and Probenecid

Two drugs might use the same transporter to be secreted into the nascent urine.

If both these drugs are present in the blood at the same time, they will compete for this receptor, and thus will have a longer half life in the body

24
Q

Which molecules are actively reabsorbed by the nephron?

A

Glucose

25
Q

Which molecules are passively reabsorbed by the kidney?

A

Lipid soluble molecules

26
Q

How is aspiring overdose treated?

A

Forced alkaline diuresis

Bicarb + water
Aspiring trapped in the urine, will not be reabsorbed, because it is now charged.

Lots of urine will be made

27
Q

Which processes in the kidney are saturable, which aren’t?

A

Filtration: non-saturable

Reabsorption:

  • acitve: saturable
  • passive: non-saturable

Secretion: saturable

28
Q

Filtration is non-saturable. What does this mean?

A

It means that the more of the drug in the blood, the greater the concentration in the urine

29
Q

What is bioavailability?

How is it calculated?

A

The amount of drug that makes it to the circulation

Bio. = in blood / administered

30
Q

What happens to drugs that aren’t very bioavailable?

A
  • Destroyed in the GIT
  • Insoluble
  • Hepatic first pass metabolism
31
Q

In what circumstances is a drug 100% bioavailable?

A

Intravenous injection

32
Q

What factors affect bioavailability?

A

I/ Absorption

  • transit time
  • emptying time

II/ Destruction

  • enzyme polymorphisms
  • disease
  • competition
  • enzyme inhibitors
33
Q

What happens to the size of the dose as bioavailability decreases?

A

Dose increases

34
Q

What is volume of distribution?

A

The theoretical amount of blood with the given concentration of the drug, required to have the same amount of the drug in the blood as the plasma

35
Q

How is Vd calculated?

A

Vd = amount in body / plasma concentration

In litres

36
Q

What does it mean if a drug has a very high volume of distribution?

A

It is being sequestered out of the blood into other body compartments

37
Q

What is the lowest theoretical Vd?

In what circumstances would this occur?

A

Around 5L

If all the drug was in the plasma
ie bound to a protein in the plasma

38
Q

What factors influence Vd?

A

Protein binding

Access to body compartments

Lipid solubility

39
Q

How is clearance calculated?

What is the unit?

A

Clearance = metabolism + excretion / plasma concentration

Litres / min

40
Q

How is half life calculated?

A

Vd x Clearance

Unit is 1/min

41
Q

What affects clearance?

A 
Liver function
Renal function
- Polymorphisms
- Disease
- Competition
- Enzyme inhibitors
42
Q

What is half life?

A

The time it take for drug plasma concentration to fall by half

43
Q

Drugs that obey first order pharmacokinetics have what sort of half life?

A

Fixed

44
Q

What affects half life?

A

Clearance

Vd

BIOM20002 - HSF (60 decks)

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