List the properties of the ideal inotrope (50% of marks). How does adrenaline compare with respect to these ideal properties? (50% of marks).
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
| Property | Adrenaline |
| Pharmaceutics | |
| 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 |
| Pharmacokinetics | |
| 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 |
| Pharmacodynamics | |
| 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 |
| Safety | |
| 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.