Distribution Flashcards Preview

BMSC1212 Introduction to pharmacology > Distribution > Flashcards

Flashcards in Distribution Deck (27)
Loading flashcards...
1
Q

What is distribution?

A

The reversible movement of drugs from the systematic circulation to the cells and interstitial tissues

2
Q

What do highly porous capillaries allow?

A

Paracellular diffusion

3
Q

What does the penetration of drugs into cells depend on?

A

Molecular size, lipid solubility and degree of ionisation

4
Q

Why may lipid solubility be important to a drug?

A

Some drug receptors are situation within cells

5
Q

What is HMG CoA reductase

A

The enzyme inhibited by the statin group of drugs used to lower bloop lipids in the treatment of hyperlipidaemia

6
Q

Why can insulin not cross the plasma membrane?

A

Too large (large molecular mass)

7
Q

Why can atracurium not cross the plasma membrane?

A

Highly ionised

8
Q

What is perfusion?

A

Blood flow

9
Q

Where is onset of action slower?

A

Skin, fat and bone

10
Q

What is the distribution of hydrophilic and large molecular weight drugs rate-limited by?

A

The permeability of the blood-tissue boundary

11
Q

Why does anaesthetic thiopental have a very short duration of action?

A

Time-dependent redistribution into fat, depletion in the brain.

12
Q

What is redistribution

A

The transfer of a drug from the brain, back into the blood and then into peripheral organs

13
Q

How do polar drugs exit the blood brain barrier?

A

Carrier-mediated transport

14
Q

How do large hydrophilic drugs exit the blood brain barrier?

A

Fenestrations

15
Q

How can some drugs be pumped back into the lumen?

A

P-glycoprotein, situated on the luminal surface of the endothelial cell plasma membrane

16
Q

Why is the CNS surrounded by a barrier?

A

Make it difficult for hydrophilic substances to penetrate, tight junctions do not allow paracellular diffusion

17
Q

Give three examples of drugs which can penetrate the blood-brain barrier by carrier mediated transport

A
  1. Salicyclic acid
  2. Valproic acid
  3. L-DOPA
18
Q

How is L-DOPA transported into the brain?

A

By the L-system, transports large neutral amino acids

19
Q

What is required in the brain to treat Parkinson’s disease and why is this a problem?

A

Dopamine, cannot cross the blood brain barrier

20
Q

What converts L-DOPA to dopamine and why is this a problem?

A

DOPA decaroboxylase, converts L-DOPA in the periphery, reducing the amount able to cross the BBB

21
Q

What does carbidopa do?

A

Blocks DOPA decarboxylase, cannot cross the BBB, serves to increase peripheral L-DOPA levels and does not inhibit dopamine conversion in the brain.

22
Q

What is the placenta?

A

A structure that separates foetal and maternal blood

23
Q

How does the placenta behave?

A

Like a lipid membrane, acts as a metabolic barrier contains a variety of enzymes cyt p450s, dependent mono-oxygenases and monoamine oxidases to metabolise substrates.

24
Q

What can bound drugs not do?

A

Exit the blood system due to the high molecular mass of the protein-drug complex.

25
Q

What is the effect of aspirin on warfarin?

A

Increases the unbound concentration and enhances its pharmalogical effects

26
Q

What is a sequestered drug?

A

one which has accumulated to a concentration higher than in blood or plasma.

27
Q

What happens to highly lipid soluble drugs in adipose tissue?

A

Accumulates such that their concentration in this tissue is many times that in blood.