Aspirin - Metabolism and Elimination

Question 1

What type of compound is Aspirin?

What increases its excretion?

What reaction occurs with Aspirin?

Answer 1

• Weak acid
• Increased urine pH
• Proton donor; HAsp (unionised) ⟷ H+ + Asp-

Question 2

How is it absorbed?

How is it distributed?

How is it excreted?

Answer 2

• • Stomach is acidic; higher amount of unionised HAsp (lipid soluble)
  • Unionised HAsp crosses gastric mucosa into plasma
• • Plasma is slightly basic; unionised HAsp is quickly ionised to Asp-
  • Asp- can’t pass back into stomach due to Ion trapping
• • Glomerular filtration; Asp- is NOT bound to plasma protein
  • Passive diffusion; uses concentration gradients
  • Tubular secretion; uses specific anion transporters

Question 3

What occurs with Aspirin in Acidic urine?

What occurs with Aspirin in Basic urine?

How can you treat drug overdose by affecting urine pH?

Answer 3

• • Aspirin acts as a proton acceptor
  • Forms Unionised HAsp, which is reabsorbed into the blood
• • Aspirin acts as a proton donor
  • Forms Ionised Asp-, which is excreted
• BASIFY urine