Clinical Significance

Digoxin is a potent cardiac glycoside used to treat atrial fibrillation with rapid ventricular response, and to treat congestive heart failure.  Test results are used to monitor levels of digoxin because the drug has a low therapeutic ratio (a small difference between therapeutic and tissue toxic levels), and because the symptoms of drug overdose may resemble the original condition for which the drug was prescribed.  Also, digoxin dosage may require adjustment when renal function is impaired or when drugs known to alter the pharmacokinetics of digoxin are co-administered.  Monitoring serum or plasma digoxin levels along with other clinical data can aid the physician in adjusting patient dosage to achieve optimal therapeutic effect while avoiding sub-therapeutic or toxic dosage levels. Toxic symptoms may occur at levels lower than critical limit.  Steady state is reached in 5 days.  Digoxin has an average half-life of 48 hours, is 25% protein bound, and is cleared by the kidneys.