An 88-yeаr-оld mаle with а PMH оf atrial fibrillatiоn, hypertension, and BPH presents to your office for follow-up after starting a new medication to monitor his potassium levels. Current medications include: hydrochlorothiazide 25 mg orally daily, digoxin 0.125 mcg orally daily, lisinopril 10 mg orally daily, apixaban 5 mg orally twice daily and metoprolol succinate 25 mg orally daily. He reports nausea, blurred vision and mild confusion. His pulse is 48 beats/min. Laboratory studies reveal low serum potassium levels and reduced renal function. Which of the following best explains why careful monitoring of this medication is required?