Drug distribution and excretion Flashcards Preview

Principles of disease JK > Drug distribution and excretion > Flashcards

Flashcards in Drug distribution and excretion Deck (25)
Loading flashcards...
1
Q

Distribution

A

Reversible transfer of a drug between the blood and the extra vascular fluids and tissues of the body eg muscle, fat, brain

2
Q

What 6 things effect tissue distribution?

A
Disease and other drugs
tissue perfusion
Membrane characteristics 
Plasma protein binding 
Elimination
Transport mechanism
3
Q

Membrane characteristics

A

Blood-brain barrier

Blood testes-ovary barrier, lipid soluble drug, active transport

4
Q

Plasma protein binding

A

Drug bound to albumin eg phenytoin

Binding is reversible and can be changed in response to renal failure, pregnancy etc.

5
Q

Is an unbound drug active or inactive

A

Active

6
Q

What 3 things effect the therapeutic range

A
  • Clearance
  • Volume of distribution
  • Half life
7
Q

Clearance (ml/min)

A

Theoretical volume of fluid from which a drug is completely removed over a period of time

8
Q

What is clearance dependent on?

A
  • Metabolism and biliary secretion

- Concentration and urine flow

9
Q

Volume of distribution (Vd)

A

Volume in which the amount of drug would be uniformly distributed to produce the observed blood concentration

10
Q

What does a greater Vd mean?

A

Greater ability to diffuse into/through membrane

11
Q

What should the Vd be?

A

42L

12
Q

Half life (t1/2)

A

Time taken for the drug concentration in the blood to decline to half of current value
Depends on Vd and clearance

13
Q

What does an increased half life mean?

A

Increased toxicity

14
Q

To have an effect what should a drugs concentration and half life be?

A
  • Steady concentration between therapeutic range

- 4-5 half lives before stabilisation

15
Q

Drug elimination

A

Removal of active drug and metabolites from body

Determines length of action

16
Q

What does drug elimination depend on?

A

Drug metabolism (liver) and excretion (kidneys)

17
Q

What are the primary organs for drug excretion?

A

Kidneys - renal failure cause toxicity

18
Q

How much does glomerular filtration filter a day?

A

190L of unbound drug

19
Q

Passive tubular reabsorption

A

Through tubule into circulation - distal tube and collecting duct - unionised eg weak acid

20
Q

Active tubular secretion

A

Secrete into proximal tube ( acid and alkali)

Protein bound cationic and anionic drug

21
Q

How much drug elimination does bilary secretion make up?

A

5-95%

22
Q

How much bile does the liver secret a day?

A

1L

23
Q

Describe biliary secretion

A

Drugs secreted into bile and reabsorbed in circulation -enterohepatic circulation
Occurs until drug metabolised in liver or excreted

24
Q

What does metabolism in liver lead to?

A

Conjugation of drug - not reabsorbed from intestine

25
Q

What does liver damage lead to?

A

Decreased conjugation and biliary secretion

Build up and reabsorption of drug = TOXICITY