Digoxin: serious drug interactions.

Digoxin has a narrow therapeutic margin and potentially life-threatening cardiac adverse effects. Gastrointestinal disorders, neuropsychological disorders and bradycardia are warning signs. Some drug combinations can aggravate the cardiac adverse effects of digoxin, or reduce its efficacy. We reviewed the literature, using the standard Prescrire methodology, in order to examine which drugs are involved in these interactions, and the mechanisms involved. Most relevant data are based on small pharmacokinetic studies or detailed case reports. The adverse effects of digoxin are potentiated by renal impairment, which may be pre-existing or due to nephrotoxic drugs such as nonsteroidal antiinflammatory drugs (NSAIDs), angiotensin-converting-enzyme (ACE) inhibitors, angiotensin II receptor antagonists and ciclosporin. Some coadministered drugs such as macrolides and cardiovascular drugs (especially amiodarone) can cause digoxin overdose through pharmacokinetic interactions. The mechanism most often implicated is inhibition of P-glycoprotein, of which digoxin is a substrate. Hypercalcaemia and hypokalaemia inducing drugs, heart-rate lowering drugs, and drugs that prolong the QT interval or slow cardiac conduction can potentiate the cardiac adverse effects of digoxin. Plasma concentration of digoxin is not affected. Several drugs, including sucralfate, acarbose, cytotoxic agents, and enzyme inducers, can reduce digoxin plasma concentrations. This effect is attributed to decreased gastrointestinal absorption or increased elimination of digoxin. In practice, patients treated with digoxin, and their caregivers, should be aware that digoxin has a narrow therapeutic margin and frequent and potentially severe adverse effects. Close clinical monitoring is necessary to detect early warning signs (bradycardia and gastrointestinal or neurological disorders). Digoxin assay alone is not always sufficient. Special care is required for patients with renal failure, the elderly and patients receiving potentially interacting drugs.