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Drug Excretion


By Kidney

               Penicillin         Diazepam
(Almost cleared completely in single transit)
Other drug lie with in Range
(Extremely slowly)

Fundamental Processes:

  1. Glomerular filtration
  2. Acute tubular secretion
  3. Passive diffusion across tubular epithelium

Glomerular Filtration:-

  1. ˂ 20000 kDa freely filtered exception Heparin (smaller but due to negative charge)
  2. Highly protein bound drug:- not filtered e.g, warfarin 98% bound to albumin

Tubular Secretion:-

  1. Mainstay of drug removal process
  2. Use active carrier process (Energy dependent)
  3. May remove drug completely from blood
  4. Clear the drugs which are protein bound

Carrier transport system

Organic acid (anionic)

Organic basic (cationic)

  • Probenecid
  • PAH,
  • Penicillin,
  • Furosemide
  • Amiloride
  • Dopamine, Histamine
  • Morphine, Pethidine
  • Quinine


*Substrate competition hence Probenecid retards the secretion of penicillin hence prolongs action.


Diffusion across renal tubule

-         Passive reabsorption of 99% of glomerular filtrate from tubules as isosmotic of plasma filter2-3 L of urine produced

  • Lipophillic drugs are almost reabsorbed
  • Highly polar drugs are not reabsorbed
  • Weak Ions: (May change their ionization based on using PH 6-8)

Weak acids

Weak bases

  • Barbiturates, Aspirin
  • Excreted on Alkalization of urine
  • Atropine, Strychnine, Morphine
  • Excreted on Acidification of urine


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