Outline the kinetic characteristics and the mode of action of digoxin.  (75% of marks)

List the cardiovascular effects of digoxin (25% of marks).

[Click here to toggle visibility of the answers]

College Answer

The Syllabus for the Primary examination describes an outline to be “Provide a summary of
the important points.” Thus candidates were expected to briefly mention the fundamental
pharmacokinetic characteristics (eg highly lipid soluble, well absorbed from small intestine,
oral bioavailability of 60 - 90%, protein binding of 20 - 30%, volume of distribution, half life,
etc) and mode of action. This was poorly done and candidates’ answers often lacked
structure.


The question outlines the distribution of marks, being 25% for listing cardiovascular effects.
Thus candidates were expected to broadly list the important cardiovascular effects relating to
mechanical (eg increase intensity of myocardial contraction, direct venous and arteriolar
constriction, etc) and electrical ( increase phase 4 slope & automaticity, hyperpolarization,
shortening of atrial action potentials, decrease AV conduction velocity and prolong AV
refractory period, increase PR & QT intervals, dose and baseline autonomic activity
dependent actions, etc).

Syllabus – C2c 2a, b
Reference: Basic and Clinical Pharmacology, Katzung. 9TH Ed. Chapter 13 page 206
Goodman & Gilman's The Pharmacological Basis of Therapeutics