Serum
digoxin levels are increased by about 40% by
verapamil 160 mg daily, and by about 70% by
verapamil 240 mg daily.
Digoxin toxicity may develop if the dosage is not reduced. Deaths have occurred as a result of this interaction.
An initial 33 to 50% dosage reduction has been recommended for
digoxin. The interaction develops within 2 to 7 days, reaching a maximum within 14 days or so. Monitor
digoxin levels during this period.