Digoxin Pharmacokinetics and Pharmacodynamics

Questions provided by Nicholas C. Schwier, Pharm.D.

Question 1. KXJ is a 54 year-old female with a past medical history of Type 2 Diabetes mellitus and Hypertension, who is admitted for paroxysmal atrial fibrillation. Your attending would like to start daily digoxin (orally: F = 0.7) as a tablet formulation and asks you for a dose recommendation for KXJ. Currently her heart rate is 123 bpm. KXJ's height is 75 inches, she weighs 128 lbs., and her serum creatinine has been 1.27 mg/dL for the last year.

Calculate a maintenance dose that will achieve a serum digoxin level of 1.04 ng/mL at steady state. Round to the nearest half tablet (0.125 mg/2).
Assume: Total ClDigoxin (mL/min)= (0.8 mL/kg/min)(wt in kg) + (CLcr(mL/min)

Question 2. A few weeks after you start KXJ on your calculated digoxin dose, she is started on a drug called rifampin and has a steady-state digoxin level drawn. The laboratory reports that the level is actually 0.915 ng/mL. Calculate a new maintenance dose, to the nearest half tablet (0.125 mg/2), that will achieve a serum digoxin level of 1.04 ng/mL at steady state.

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Some Equations:

IBW equation (male)
Equation 27.2.1 IBW for Male Patients

IBW equation (female)
Equation 27.2.2 IBW for Female Patients

Creatine Clearance C-G Equation
Equation 27.2.3 Creatinine Clearance (Cockcroft-Gault Equation)

Steady State Concentration Equation
Equation 27.2.4 Steady State Concentration

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