Pharm 101: Captopril

Class

ACE-inhibitor

Pharmacodynamics
  • ACE-I inhibit the Renin-Angiotensin-Aldosterone (RAA) system, and stimulate the Kallikrein-Kininogen (KK) system, by inhibiting peptidyl dipeptidase (angiotensin converting enzyme), an enzyme that:
    • Hydrolyses angiotensin I to angiotensin II
    • Inactivates bradykinin, a potent vasodilator
  • Angiotensin II is a potent vasoconstrictor and also leads to aldosterone secretion that causes Na and water retention
Pharmacokinetics
  • Bioavailability 65%
  • Half-life 2 hours
  • Renal excretion
Clinical uses
  • Hypertension
  • Chronic renal failure:
    • Diminish proteinuria and stabilise renal function (even in absence of lowering BP_
    • Recommended in diabetes even in absence of hypertension
  • CCF
  • Reduced mortality post-MI
Adverse effects
  • Marked first-dose hypotension, particularly in dehydrated patients
  • Acute kidney injury, especially with bilateral renal artery stenosis or solitary kidney
  • Hyperkalaemia, especially with K sparing diuretics, diabetes or CRF
  • Dry cough and angioedema (due to bradykinin and substance P)
  • Neutropenia or proteinuria if given in high doses to CRF patients
  • Minor toxic effects in 10% of patients:
    • Altered sense of taste
    • Allergic skin rash
    • Drug fever
Precautions/contraindications
  • Pregnancy:
    • First trimester: teratogenic
    • Second/third trimester: fetal hypotension, anuria and renal failure
  • Dose should be reduced in renal failure
  • Drug interactions:
    • Potassium supplements or potassium sparing diuretics, which can result in hyperkalaemia
    • NSAIDs can impair the hypotensive effects of ACE-I by blocking bradykinin-mediated vasodilation, which is at least partially prostaglandin mediated
    • Lithium –> lithium toxicity
    • General anaesthetics –> hypotension
    • Other diuretics/anti-hypertensives –> hypotension
Further Reading
Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS CCPU (RCE, Biliary, DVT, E-FAST, AAA) Rob is an Emergency Medicine Advanced Trainee based in Melbourne, Australia. He has special interests in medical education, ECG interpretation, and the use of diagnostic and procedural ultrasound in the undifferentiated and unwell patient.

Follow him on twitter: @rob_buttner | ECG Library |

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.