Download 2-12-2016 PPT

Pharmacokinetics:
Digoxin
Allie Punke ([email protected])
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
0.125 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 1/17 @ 0230. The SDC
(drawn at 1/17 @ 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
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!