Pharmacokinetics- Excretion

Question 1

What PK interactions affect excretion?

Answer 1

• Drug excretion may be altered by pH in kidney tubule (e.g. alkalinising urine)

Question 2

Describe excretion through the lungs

Answer 2

• Volatile compound; gaseous general anaesthetics and alcohol
• Elimination dependent on extent of distribution to other organs, rate and depth of ventilation and air-blood partition

Question 3

Describe excretion through bile

Answer 3

• Large drugs and glucuronide conjugates
• Conjugation with glucuronide increases mol wt by 200Da
• Drugs eliminated in bile mixed with bile salts
• Elimination depends on bile release from gall bladder

Question 4

Describe excretion through kidney

Answer 4

• Everything thrown away
• Reabsorbed desired products
• Active expulsion of waste products

Question 5

What does glomerular filtration include?

Answer 5

• Passive filtration of 20% of plasma
• Large molecules not filtered
• Small molecules filtered including water, salts, nutrients, toxins, urea and xenobiotics

Question 6

Describe renal reabsorption and secretion

Answer 6

• Kidney tubule reabsorbs almost all wanted substances back into circulation, lipophilic drugs also reabsorbed- diffuse across tubule walls back into peri tubular capillaries
• Unwanted substances actively left in urine- hydrophilic drugs and metabolites of metabolites lipophilic drugs
• Some substances actively secreted by tubular transporters into tubules like drug metabolites conjugated with glucuronide