Core17: Excretion of drugs

🚰 High-yield / 要点：Drug elimination occurs by excretion of unchanged drug or metabolism followed by excretion. Main route is the kidney.

Definition / 定義

• Elimination = removal of administered drug from the body.
• Two main forms:
  • Excretion of unchanged drug.
  • Biotransformation/metabolism followed by excretion.

Routes of excretion / 排泄経路

Route	Mechanism / examples	High-yield point
Kidney	Glomerular filtration, tubular secretion/reabsorption, passive diffusion	Main pharmacokinetic excretion route
Biliary / enterohepatic	Digitoxin, doxycycline, ethinylestradiol, NSAIDs	Can prolong drug action via recycling
Lung	Inhaled anesthetics	Important for volatile drugs
Saliva / sweat	Minor routes	Less relevant pharmacokinetically

Renal elimination / 腎排泄

• Glomerular filtration:
  • Filters free/unbound drug.
• Active tubular secretion / reabsorption:
  • Carrier-mediated.
  • Example: probenecid blocks penicillin secretion.
• Passive tubular diffusion:
  • pH-dependent.
  • Apolar / nonpolar compounds are reabsorbed.
  • Polar/ionized compounds remain in tubules and are excreted.

Urine alkalinization / 尿アルカリ化

• Forced alkaline diuresis increases elimination of acidic drugs.
• Used in intoxication with:
  • Salicylates
  • Barbiturates
• Mechanism: ionized acidic drugs are trapped in urine and reabsorbed less.

Remember / 覚え方

• Polar = pee out
• Nonpolar = reabsorbed
• Probenecid blocks penicillin secretion
• Alkaline urine clears weak acids