Sunday, February 22, 2015

Study group discussion: Drugs and conditions that enhance Digoxin toxicity and the mechanism behind it

I read some cool things today on the group!

Why is there an increased risk of toxicity with digoxin in hypokalemia, hypercalcemia and hypomagnesemia?

Potassium and digoxin compete for the binding site so if there will be less of potassium more of digoxin gets the chance to bind leading to toxicity. The NaKATPase is the binding site.

Digoxin toxicity is aggravated by increased calcium cause more calcium accumulates intracellulary. This leads to increased contraction.
Calcium intracellularly also increases the generation of ectopic foci within contractile cells.

Magnesium is used as treatment in the treatment of toxicity.
Magnesium is the cofactor for the Na-k pump. Less magnesium..less functioning of the pump. Hence aggaravated toxicity!

Here's an additional fun concept:
Drug of choice for supraventricular tachycardia?

Answer: Verapamil.

So if you have SVT in digoxin toxicity.. Would you give verapamil?

Answer: No.

Why not?

Don't know? Let me approach the explanation in a way which helps you think better - What is the mechanism of excretion for digoxin?

Answer: Renal excretion.
Digitoxin is via hepatic.
Here's a mnemonic on renal / liver excretion of Digoxin / Digitoxin:

So when digoxin enters the tubular cell, it is excreted into the lumen via p-gp receptors. Those are the same receptors responsible for multidrug resistant. In cases of anti-cancer agents and anti-malarials. You see, verapamil is one of the rare drugs that block p-gp. Hence, decreasing digoxin excretion, thus, precipitating it's toxicity.
*pgp refers to P Glycoprotein receptors

Verapamil for the same reason is used to reverse resistance to anticancer and anti-malarials. Pretty cool info, ain't it?

I just fell in love with the whole drama digoxin plays in your body :D
So what drug is used in SVT induced by digoxin then?

Answer: Beta blocker.

That's all for today!

I'm trying to edit the stugy group discussions in a more reader friendly format. Hope you like them!



  1. Really i have got to learn many new things which were never thought in such a simple way.


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