Which medication, if prescribed, would likely increase the risk of side effects with digoxin therapy?

The medication that would likely increase the risk of side effects with digoxin therapy is verapamil. Verapamil is a calcium channel blocker that can significantly enhance the effects of digoxin by slowing down the heart rate and impacting the AV node conduction. This is particularly concerning because digoxin exerts its therapeutic actions by increasing the contractility of the heart and controlling heart rate, so the additive effects can lead to bradycardia or other cardiac complications.

When using digoxin, it is important to monitor the levels carefully, especially when a concurrent medication like verapamil is initiated, since it can lead to increased digoxin serum concentrations due to its effect on renal clearance and distribution. Consequently, there is a heightened risk of digoxin toxicity, which can manifest as gastrointestinal symptoms, visual disturbances, and severe cardiac arrhythmias.

In contrast, while furosemide, losartan, and hydrochlorothiazide are commonly used diuretics and antihypertensives, their interactions with digoxin primarily revolve around changes in electrolyte levels, which can influence digoxin's effectiveness but do not significantly elevate the risk of direct side effects from digoxin itself as verapamil does.