Cimetidine: who studied the pharmacokinetics of oral digoxin in eight healthy volunteers, both with and without concurrent cimetidine. It was reported a 25% decrease in steady state serum digoxin concentrations when digoxin was given together with cimetidine. They concluded that cimetidine had no effect on the area under the plasma concentration versus time curve of digoxin.

Vasodilator drugs: Total renal clearance of digoxin was increased by 50% in 8 patients during administration of nitroprusside or hydralazine . It is not yet known whether long-term vasodilator therapy increases the dosage requirements for digoxin in patients with congestive heart failure. Because the glomerular filtration rate was unchanged and the estimated renal blood flow was increased, the mechanism of this alteration in digoxin renal clearance was thought to be an increase in tubular secretion of digoxin.

Conclusion :

The accumulated information regarding drug interactions with digoxin should contribute to greater safety in the use of the drug, provided that the physician maintains constant vigilance whenever any medication is added to or withdrawn from a therapeutic regimen that indudes digoxin. Although there has been a tremendous increase in our knowledge of the drug interactions, more investigation is needed to define the full scope and magnitude of these interactions with digitalis, particularly during steady state. Patients with heart disease may be treated concomitantly with anticholesterolemic drugs, diuretic drugs, calcium channel blocking agents, vasodilators and antimicrobials, some of which have been shown to interact with digoxin. We are also greatly in need of accurate and sensitive methods to reliably measure the inotropic and vagotonic effects of digitalis to assess the effects of these drug interactions.