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P.O.D own flashcards > Drug distribution > Flashcards

Drug distribution Flashcards

1
Q

What must a drug do in the body to be active?

A

it must leave the blood stream and enter the inter or intracellular spaces

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2
Q

what does drug distribution mean?

A

the reversible transfer of a drug between the blood and the extra vascular fluids and tissues of the body (i.e fat, muscle and brain tissue)

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3
Q

Therapeutic range?

A

range over which they are active

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4
Q

drug elimination

A

the removal of active drug and metabolites from the body

determines length of action of the drug

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5
Q

what is bioavailability?

A

the proportion of a drug or other substance which reaches systemic circulation when introduced into the body and so is able to have an active effect

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6
Q

if 100mg of a drug are administered orally and 70mg of this drug are absorbed unchanged, the bioavailability is

A

0.7 or 70%

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7
Q

how is bio-availability determined?

A

comparing plasma levels of drug after a particular route of administration

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8
Q

factors that determine bio-availability

A
  • drug formulation
  • ability of drug to pass physiological barriers
  • gastrointestinal effects- nausea, vomiting, abdominal pain, constipation, diarrhea, and gastritis
  • first pass metabolism
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9
Q

Factors that determine drug distribution

A

chemical properties
plasma protein binding
clearance
half life

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10
Q

What is the distribution of drug between tissues dependent on?

A 
vascular permeability
blood flow
cardiac output
the ability of the drug to bind to tissue and plasma protein
its lipid solubility
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11
Q

What do chemical properties of a drug determine?

A

where it is distributed (volume of distribution) e.g lipid solubility or ionisation? in membrane etc?

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12
Q

plasma protein binding

A

many drugs bind to proteins in the plasma such as albumin or alpha1-glycoprotein
- only unbound drugs are biologically active

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13
Q

define the term clearance

A

the theoretical volume from which a drug is completely removed over a period of time.
- It is the measure of elimination.
ie volume of urine (drug moves into kidney- removed by urine- so the vol. of urine taken until drug is removed from the body)

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14
Q

What does renal clearance depend on?

A

concentration and urine flow rate

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15
Q

What does biliary excretion depend on ?

A

biliary excretion for hepatic clearance (liver)

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16
Q

Define half-life

A

time taken for the drug concentration in the blood to decline to half of the current value.

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17
Q

What does a long half life indicate

A

Drug doesn’t need to be taken very often

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18
Q

What does the half life depend on?

A

volume of distribution rate of clearance

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19
Q

Blood brain barrier

and drug distribution

A

prevents the brain uptake of most pharmaceuticals due to the epithelial-like tight junctions within the brain capillary endothelium.

20
Q

Blood-testes/ovary barrier and drug distribution

A

must be lipid soluble drugs or actively transported through membrane

21
Q

Which organ is central to renal drug excretion

A

kidneys are the primary organ for drug excretion

22
Q

What mechanisms are used in renal excretion?

A
  1. Glomerular filtration
  2. passive tubular reabsorption
  3. active tubular secretion
23
Q

Glomerular filtration

A

the first step in making urine
filter excess fluid and waste products out of the blood into the urine collecting tubules of the kidney

the glomerular flow rate is the rate of filtered fluid through the kidney

24
Q

Passive tubular re-absorption

A

solutes and water are removed from the tubular fluid and transported into the blood

25
Q

Active tubular secretion

A

transfer of materials from peri-tubular capillaries (tiny ones used for absorption) to the renal tubular lumen

26
Q

What can renal damage cause

A

drug toxicity- drug can’t be removed from the body so it accumulates

27
Q

lipid soluble drugs

A

have high vol. of distribution as they move to tissues around the body

  • can pass through membranes
  • ie to the heart, brain and liver
28
Q

Cannabis

A

highly lipid soluble

29
Q

plasma protein binding

A

many drugs bind to proteins in the plasma such as albumin or alpha1-glycoprotein

30
Q

An unbound drug is…

A
  • biologically active
  • more lipid soluble
  • can cross membrane more efficiently
31
Q

A bound drug…

A

is inactive- cannot be distributed around body- stays in blood stream

32
Q

how can the amount of bound drug be changed?

A 
renal failure 
hypoalbuminaemia ( level of albumin in the blood is abnormally low- protein in the blood)
pregnancy 
other drugs
saturability of binding
33
Q

Apparent vol of distribution

A

the vol of distribution is the vol of plasma that would be necessary to account for the total amount of drug in a patient’s body, if that drug were present throughout the body at the same concentration as found in the plasma. Litres per kg

so basically how big a volume you would need to observe the blood plasma concentration actually measured

if you gave a patient 1000mg then waited for equilibrium- drug to distribute around the body and for there to be a balance between unbound and bound drug
a blood test then said there was only 50mg per litre in the blood

1000/50 = 20 litres so 20 litres is needed to contain the 1000mg of drug at a conc of 50 mg/l in the plasma

34
Q

What does excretion by the kidney depend on?

A

glomerular filtration
passive tubular reabsorption
active tubular secretion

35
Q

active tubular secretion

A

Some drugs are actively secreted into the proximal (top) tubules of the kidneys. This is the main method of excretion for protein bound cationic and anionic drugs.

36
Q

passive tubular re-absorption

A

As the filtrate (This filtrate contains water, glucose, salts and urea) moves down the tubules of the kidneys, it becomes more concentrated, as do any drugs it carries.

Passive diffusion means that the body can reabsorb some of this drug. Only un-ionised drugs such as weak acids can be reabsorbed.

Can also be affected by renal failure.

37
Q

Glomerular Filtration

A

All unbound drugs are filtered at the glomerulus (small tuft of capillaries at end of kidney tubule) provided their size or charge aren’t excessively large. Anything that affects the filtration rate will affect the clearance rate of a drug.

38
Q

the higher the Vd means

A

greater the ability of the drug to diffuse into and through membranes ie be distributed around the body

39
Q

how can Vd be increased

A 
renal failure (fluid retention, more fluid for drug to be distributed to)
liver failure (altered body fluid and plasma protein binding)
40
Q

how can Vd be decreased

A

dehydration

41
Q

drugs with a high lipid solubility (non-polar drugs), low rates of ionization, or low plasma protein binding capabilities have…

A

higher volumes of distribution

42
Q

drugs which are more polar, more highly ionized or exhibit high plasma protein binding in the body’s environment

A

have lower volumes of distribution

43
Q

What is the theoretical Vd

A

42 litres of fluid in the body

44
Q

can you have a higher Vd than 42 litres?

A

yes just means the drug is highly distributed into tissue

45
Q

Biliary secretion

A

the liver secretes 1 litre of bile a day
drugs may be passively or actively secreted into the bile
many drugs are reabsorbed from the bile into the circulation- entero- hepatic circulation

46
Q

conjugation

A

metabolism in the liver often leads to conjugation of the drug- combination of drug and glucuronic or sulfuric acid
this conjugated drug is not reabsorbed from the intestine
damage to the liver may reduce the rate of conjucation and biliary secretion so allow the build up or reabsorption of the drug with resultant toxicity

P.O.D own flashcards (34 decks)

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