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Yr 1 - Pharmacology > Elimination > Flashcards

Elimination Flashcards

1
Q

When does elimination occur?

A

Once drug has been broken down into something more hydrophilic

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2
Q

What is elimination?

A

Removal of drug from body

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3
Q

How does blood flow to kidney affect excretion rate?

A

Influences rate of delivery of drug to kidney

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4
Q

What 3 stages does renal excretion involve?

A
  1. Glomerular filtration
  2. Tubular secretion
  3. Tubular reabsorption

The sum of these determines the net renal drug excretion

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5
Q

What will glomerular filtration remove?

A

Passive process - only removes small molecules (water soluble and unbound)

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6
Q

What is tubular secretion important for?

A

Active secretion of drugs into kidney tubule

Important for drugs that are highly plasma protein bound as these are not excreted effectively by glomerular filtration (not effected by degree to which drug is bound)

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7
Q

What happens during tubular reabsorption?

A

In renal tube, nonionised form of drug can diffuse across tubular membrane and re-enter plasma

As water is reabsorbed along renal tube –> tubular drug conc increases –> providing conc gradient favouring drug reabsorption

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8
Q

What is clearance?

A

Volume of blood/plasma cleared of drug per unit time

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9
Q

What does clearance indicate?

A

The volume of plasma from which drug is completely removed in a given time period

NOT the amount being removed

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10
Q

What is half-life?

A

Time taken for conc to deduce 50%

Assume at point of ingestion that there’s 100%

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11
Q

If drug undergoes 5 half-lives, what can you assume?

A

Less than 3% in system

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12
Q

What is half life increased by?

A
  1. Diminished renal plasma flow
  2. Addition of 2nd drug that displaces first from albumin
  3. Decreased extraction ratio (renal disease)
  4. Decreased metabolism (liver disease)
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13
Q

How can you evaluate renal function?

A

Looking at creatine

Estimation of creatine clearance - estimates clearance of drugs filtered at glomerulus

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14
Q

What is creatine?

A

Produced in skeletal muscle which is excreted through kidneys

It is neither passively reabsorbed nor actively secreted

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15
Q

What is eGFR?

A

Estimating Glomerular Filtration Rate

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16
Q

What is Cockcroft Gault Equation?

A

Estimated creatine clearance in mL/min

17
Q

What is eGFR in relation to?

A

Muscle mass not actual weight - rugby player with large muscle mass would appear to have poor creatine clearance

Not good indicator but can show renal impairment

18
Q

What is Cockcroft Gault equation good indicator of?

A

How well someone’s kidneys are functioning - important to use during renal dosing

19
Q

What does elimination via the liver depend on?

A

Blood flow to liver and activity of enzymes in liver

20
Q

What do liver enzymes alter the drug to form?

A

Metabolites which are inactive or equally or more active than parent drug

21
Q

To be efficiently excreted in urine, what must drug be?

A

Water soluble and not too tightly bound to proteins in bloodstream

22
Q

What is the glomerular filtration rate affected by?

A

Disease/age

23
Q

How does excretion differ in children and elderly?

A

Children –> reduce capacity due to immature kidneys

Adults –> reduction due to impaired glomerular filtration rate

24
Q

What is glomerular filtration?

A

Kidneys filter excess fluid and waste products out of the blood to form the glomerular filtrate

25
Q

What are the main products excreted in urine?

A
  • Metabolic waste products - e.g., urea and creatinine
  • Electrolytes (including sodium, potassium, calcium, chloride and bicarbonate)
  • Water
26
Q

What is glomerular filtration caused by?

A

The force of the difference between the outward and inward pressure (pressure gradient in the glomerulus)

27
Q

What is the outward pressure?

A

The force of the pressure exerted from the pressure of the blood vessel itself –> driving force that pushes filtrate out of capillaries

28
Q

What is the inward pressure?

A

Hydrostatic pressure of fluid within the urinary space

Pulling force exerted by albumins left in capillaries that tend to pull water back into circulatory system

29
Q

What is tubular reabsorption?

A

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

30
Q

What happens to reabsorbed solutes and water?

A

Returned to the bloodstream and not excreted as urine

31
Q

Describe passive diffusion during tubular reabsorption

A

Passing through plasma membranes of the kidney epithelial cells by concentration gradients

32
Q

Describe active transport during tubular reabsorption

A

Membrane-bound ATPase pumps (such as NA+/K+ ATPase pumps) with carrier proteins that carry substances across the plasma membranes of the kidney epithelial cells by consuming ATP.

33
Q

Describe cotransport during tubular reabsorption

A

This process is particularly important for the reabsorption of water. Water can follow other molecules that are actively transported, particularly glucose and sodium ions in the nephron

34
Q

How is water mainly reabsorbed?

A

By the cotransport of glucose and sodium.

35
Q

What is the Na+/K+ ATPase?

A

An ATPase pump that consumes ATP to facilitate the active transport of ions in the filtrate of the nephron

36
Q

What is tubular secretion?

A

Opposite process of reabsorption –> transfer of materials from peritubular capillaries to the renal tubular lumen

Urine is the substance leftover in the collecting duct following reabsorption and secretion

37
Q

What substances are secreted into the tubular fluid for removal from the body?

A 
Potassium ions (K+)
Hydrogen ions (H+)
Ammonium ions (NH4+)
Creatinine
Urea
Some hormones
Some drugs (e.g., penicillin)
38
Q

What is the tubular secretion of H+ and NH4+ involved in?

A

Blood pH regulation

39
Q

What type of process is pH regulation primarily?

A

A respiratory process, but tubular secretion assists

Yr 1 - Pharmacology (10 decks)

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