Pharmacokinetics: Digoxin Allie Punke

The Basics What is the Volume of Distribution? What body weight should we use? Why? How is it eliminated? What is therapeutic range? Do we need to worry about protein binding interactions?

The Basics—True or False Most of the drug stays in the central compartment. The drug concentration closely correlates with the effect of digoxin. Digoxin should not recommended for a patient who requires acute control of heart rate. Your patient, who exercises 4-5 times a week, develops atrial fibrillation. Digoxin would be a reasonable recommendation in this patient. For pharmacokinetics purpose, we can assume a one compartment model.

Application—Half Life A male patient (56 years, 70 kg, 5’10”, Scr=1.1) is admitted to the hospital for digoxin toxicity. The level was 4 ng/ml. How long will it take for the digoxin level to decrease to 1 ng/ml if no interventions are made?

Application--Toxicity What are some symptoms you would expect the previous patient to be experiencing?

Application--LD A female patient (98kg, 5’6”) is in the hospital and needs to be loaded with digoxin for rate control secondary to atrial fibrillation. If a goal level of 1 ng/ml is targeted, what IV loading dose do you recommend?

Application--LD A female patient (98kg, 5’6”) is in the hospital and needs to be loaded with digoxin for rate control of her atrial fibrillation. If a goal level of 1 ng/ml is targeted, what oral loading dose do you recommend? F=0.7.

Application--MD A male patient (75 kg, 5’11”, SCr=1.3, 78 years old) has been loaded for rate control of his atrial fibrillation. If a goal level of 1 ng/ml is targeted, what maintenance do you recommend? F=0.7. A week later, he comes for a follow-up visit. He reports he feels “better” and has less shortness of breath throughout the day. His last dose was last night at 9 pm. Should we draw a digoxin level today? If so, when do you recommend drawing it?

Application--SDC SDC are indicated in patients who:

Application--Steady State A patient (60kg, 6’1”, Scr=1.2, 59 years old) has been receiving mg of digoxin. Today, his SDC is 0.5. A goal of 1 ng/ml is targeted. What do you recommend regarding his digoxin dose? F=0.9

Application--SDC A patient was loaded with digoxin at The SDC (drawn at 0600) was 3. The medical resident asks for you recommendation on how to manage this patient’s digoxin dosing. He wants to know how much you would recommend lowering the digoxin dose?

Application

Name the drug interaction: Antacids Verapamil ACEI + NSAID + diuretic Rifampin Amiodarone Bile acid sequestrants Antibiotics

Summary--Equations to Know LD (To get a level around 1.4 ng/ml) IV = ____ micrograms/kg IBW Oral= _____ micrograms/kg IBW Separated into ___ to ____ doses Maintenance Dose Digoxin clearance Adjusting a dose AT steady state

Summary--Equations to Know Estimating half-life of digoxin

Summary Remember the key equations to calculate LD and MD. Recognize common drug interactions and the mechanism of how they occur (affecting F/CL) Be able to clinically interpret a SDC. Remember the 3 major organs affected by toxicity and the symptoms they produce. Only get a SDC if it is indicated.

Questions? Good luck!