On Dig. toxicity

 Q: All of the following make chances of digoxin toxicity higher except?

A) hypokalemia 

B) hypomagnesemia 

C) hypercalcemia 

D) hypoxemia 

E) hyperthyroidism

Answer: E

Digoxin over the years is falling out of favor due to its narrow therapeutic index. Also, it can be affected by various electrolytes and underlying diseases particularly hypokalemia, hypomagnesemia, hypercalcemia, and hypothyroidism. In ICU, ventilated patients are prone to go into atrial fibrillation with the rapid ventricular rate (AF with RVR). Care should be taken while loading digoxin in such patients as hypoxemia increases the sensitivity of digoxin. Loading dose should be curtailed or guided by clinical response. 

Another issue is with digoxin's large volume of distribution. It gets widely distributed to skeletal and cardiac muscles as well as to lean tissues of the body. Patients with low muscle mass should have a limited loading dose. On the other hand, obese patients should not get a higher dose as dosing is based on body estimated lean weight and not on actual weight. Also, patients with renal insufficiency should get a conservative dose.

Answering the above MCQ - hypothyroidism reduces the volume of distribution and so the plasma clearance of digoxin and vice versa happens in hyperthyroidism (choice E).

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References:

1. MacLeod-Glover N, Mink M, Yarema M, Chuang R. Digoxin toxicity: Case for retiring its use in elderly patients?. Can Fam Physician. 2016;62(3):223-228. 

2. Should Digoxin Continue To Be Used for the Management of Atrial Fibrillation?. Can J Hosp Pharm. 2017;70(5):391-394. doi:10.4212/cjhp.v70i5.1701