Pharmacodynamics question

Question

An 85-year-old, 60-kg woman with a serum creatinine of 1.8 mg/dL has atrial fibrillation. A decision has been made to use digoxin to control the rapid heart rate. The target concentration of digoxin for the treatment of atrial fibrillation is 2 ng/mL. Tablets of digoxin contain 62.5 micrograms and 250 micrograms (mcg). What maintenance dose would you recommend?

Answer 1

Your patient is average weight, with a mildly elevated creatinine, not unusual for her age. Digoxin comes in .125 and .250 mg tablets. Since the half life is 36 hours, you have to do this with caution. If there is no hemodynamic emergency about this, you would probably start with .125 mg daily, watch her heart rate over the next few days, and get a dig level in 5-7 days. You'll want to monitor her K as well. 2.0 is on the high range for a target for a-fib with rapid response.

In an emergent situation, hemodynamic instability, or for a patient with a normal creatinine, you might want to give an initial loading dose of .250 mg, or even consider slow IV admin.

With a 36 hr half-life, a dig level will not stabilize for about 5 half-lives, or a week or so. In the meantime, you can get a good idea of her dig level by observing her heart rate, EKG, and potassium level. Any bradycardia, EKG changes or low potassium may indicate toxicity.

I hope this wasn't too confusing and I hope I answered your question. In my experience, her dose is likely to be .125 daily. You could increase it or decrease it slightly by going up to 8 tablets or down to 6 tablets a week, due to the long half life. No doubt other physicians may have a slightly different answer for you.

Feel free to message me if you have any questions.