As I talked before, another common drug that being asked frequently in MRCP is digoxin. This drug is commonly used in patient with atrial fibrillation for rate control. A lot of candidates misunderstand that digoxin can be used for cardioversion. You mustmember that digoxin is being used to control the rate of atrial fibrillation ( such as beta blocker ) and will never cardiovert AF back to sinus rhytm. Another indication for digoxin is in heart failure and no study so far proves that it improves patient's survival.
There are a few conditions that can enchance digoxin toxicity such as, ( common MRCP question!)
a) hypokalaemia- therefor in clinical practice, always check patient's K level before starting digoxin. The explanation behind this toxicity,I think you have to check your pharmacology book!
b) verapamil, beta blocker , quinidine and amiodarone- because all these drugs reduce renal digoxin clearance by competing for the active tubular secretory mechanism in the distal convoluted tubule.
c) elderly and renal failure patient- due to reduced excretion!
d) other electrolyte abnormality such as hypomagnesiamia and hypercalcaemia.
Questions:
1)A 67 year old man presents with sudden onset atrial fibrillation (ventricular rate of 150/minute). His serum creatinine concentration was 250 umol/L (70-110).
What is the main factor that determines the choice of loading dose of digoxin in this patient?
1 ) Absorption 2 ) Apparent volume of distribution 3 ) Lipid solubility 4 ) Plasma half-life 5 ) Renal clearance
ANSWER: 5
2)Serum digoxin concentrations are increased when given with...EXCEPT
A Amiodarone B Spirolactone C Cholestyramine D Quinine E Verapamil
ANSWER: C
3) A 72 year old man is admitted with fast atrial fibrillation but is receiving treatment with digoxin. An inadequate dose is suspected. A sample of blood is drawn six hours after the last dose of digoxin and a plasma concentration is requested.
Which of the following factors explains the six hour wait before measuring the digoxin concetration?
1 ) enterohepatic circulation 2 ) the rate of absorption 3 ) the rate of clearance
4 ) the rate of distribution 5 ) the rate of elimination
ANSWER: 4
4)A 65-year-old was advised to start oral digoxin at a dose of 250 µg daily. His physician explained that the full effect of this treatment would not be apparent for at least a week.
Which one of the following pharmacokinetic variables did the physician use to give this explanation?
1 ) bioavailablity 2 ) half-life 3 ) plasma protein binding 4 ) renal clearance 5 ) volume of distribution
ANSWER: 2
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