Question 18

List the properties of the ideal inotrope (50% of marks). How does adrenaline compare with respect to these ideal properties? (50% of marks).

[Click here to toggle visibility of the answers]

College Answer

Inotropes are drugs that increase the force and velocity of myocardial contraction resulting 
in increased contractility and stroke volume and hence cardiac output.Good answers were 
those that adopted a systematic approach, such as providing a coherent list of ideal 
properties that included pharmaceutical, pharmacokinetic and pharmacodynamics 
characteristics, and then contrasted adrenaline against that list. The area less well covered 
was that of those aspects of adrenaline that made it less than an ideal inotrope, e.g. it 
increases myocardial oxygen consumption, causes tachyarrhythmias,tolerancemay 
develop, hyperglycaemia, lactic acid production, etc


Properties of an Ideal Inotrope, and

How Adrenaline Compares

Property Adrenaline
Cheap and widely available A box of 25 ampoules retails for $399.96
Long shelf life Shelf life of glass ampoules is 2 years, provided they are stored out of direct sunlight
Compatible with other infusions No, usually needs to run in its own lumen
Administered by a range of routes IV, IM, subcutaneous, nebulised, topical, as eye drops and directly into the ETT during an arrest.
Rapid onset and offset Onset of action within one circulation time; half life ~ 2-3 minutes; easily titratable
Cleared in a non-organ-dependent manner Adrenaline is rapidly metabolised by COMT and MAO
Inactive and inert metabolites Metabolic byproducts of adrenaline have no activity
Directly acting Adrenaline directly acts on adrenergic receptors
Lacks tolerance or tachyphylaxis No tolerance
Does not cause tachycardia Causes plenty of tachycardia
Demonstrates lusitropy Adrenaline is lusitropic, but this is often concealed by the tachycardia
Energy-neutral Significantly increases myocardial oxygen consumption
Safe in pregnancy Category C
Wide therapeutic index Significant complications occur with high doses, but these are 50-100 times larger than the low doses.


Elliott, Peter. "Characteristics of an ideal inotrope." Anaesthesia & Intensive Care Medicine 9.7 (2006): 326-330.