What should we know about digoxin PK to be able to interpret Mr. D.K.’s plasma digoxin levels?

Question

Mr. D.K. is a 67 y/o male admitted to the hospital on 3/23 because of CHF. He is on digoxin since last October and regularly takes the prescribed dose once daily. Plasma measurements of digoxin was ordered and the following digoxin levels were determined:

3/23                8:25 AM        1.2 ng/ml

3/24                 9:05 AM        0.4 ng/ml

What should we know about digoxin PK to be able to interpret Mr. D.K.’s plasma digoxin levels?

Answer 1

Digoxin clearance follows linear pharmacokinetics. Assuming that the digoxin level was drawn at the correct time and that the patient has stable renal function, the clearance should be predictable. For example, a patient is taking a maintenance dose of 0.25mg daily and the concentration results at 1.6 ng/mL. If the desired concentration is 0.8 ng/mL, then you would want to reduce the dose to 0.125mg (a 50% reduction) to achieve the desired concentration.