2018.2 SAQ 10 – positive inotropes

Outline the mechanisms of action of the drugs, with examples, which increase myocardial contractility.

BT_PO 1.52  Describe the mechanism of action of sympathomimetic … drugs used clinically
BT_PO 1.53  Describe the pharmacology and clinical application of adrenergic agonists
BT_PO 1.60  Describe the pharmacology of drugs used to manage acute or chronic cardiac failure, including: sympathomimetics, phosphodiesterase inhibitors, digoxin, ….

T / F  noradrenaline has no inotropic effect because it is a pure alpha-1 adrenergic agonist

T / F  adrenaline exerts a positive inotropic effect via beta-2 adrenergic receptors on the cardiac myocytes

T / F  milrinone is a phosphodiesterase inhibitor – it works by inhibiting the breakdown of phosphokinase A

T / F  glucagon is a positive inotrope – it works in this way by upregulating the numbers of adrenergic receptors

T / F  levosimendan works by ‘sensitising’ troponin C to the effect of calcium

T / F  digoxin’s positive inotropic effect stems from its inhibition of the Na/K-ATPase

BT_PO 1.60 : Digoxin

Describe the pharmacology of drugs used to manage acute or chronic cardiac failure, including: sympathomimetics, phosphodiesterase inhibitors, digoxin, diuretics, ACE inhibitors, nitrates and beta blockers

 

A guest post from an ex PEX chair :

Agatha Christie knew a lot about poisoning, probably as a result of working with a pathologist.  (https://bookshop.theguardian.com/catalog/product/view/id/323440/).  After reading this book, you would have to be brave to go into an English garden.
   
One of her garden poisons was foxglove, which made me think of digoxin.   As did the recent death of Miles Vaughan Williams, who classified anti arrhythmics.   So often we see digoxin toxicity in clinical practice.     An old drug, but one that continues to be used, and is loved by examiners because it allows for candidates to demonstrate  an understanding of many different facets of pharmacology.    

TRUE/FALSE  Digoxin is highly protein bound, hence the introduction of another highly protein bound drug is likely to precipitate toxicity

TRUE/FALSE  Digoxin is primarily excreted renally, and frequently patients who are prescribed digoxin may have borderline or impaired renal function which may precipitate toxicity

TRUE/FALSE  Overdosage of digoxin may be treated using Digibind (R)  which is an example of an immunoglobulin which binds to digoxin to cease its therapeutic effect

TRUE/FALSE  Hypokalaemia is frequently seen in digoxin toxicity, reflecting digoxin’s inhibition of the Na/Ca pump

TRUE/FALSE  The bioavailability of digoxin is reasonably high (approx 70%) allowing for oral loading doses to be only slightly slower in reaching therapeutic effects compared with intravenous loading doses