Final answer:
A 70-year-old woman on furosemide is experiencing symptoms of hypokalemia due to increased urinary excretion of potassium, which is a side effect of her medication. The treatment could include potassium supplementation, potentially administered intravenously in severe cases.
Step-by-step explanation:
The symptoms experienced by the 70-year-old woman taking furosemide (loop diuretic) for congestive heart failure, such as weakness, fatigue, and leg cramping, combined with her low plasma potassium levels, suggest a condition called hypokalemia. Hypokalemia occurs due to the increased excretion of potassium in the urine, a side effect of taking loop diuretics. These drugs inhibit the reabsorption of sodium (Na+) and chloride (Cl-) ions in the ascending limb of the loop of Henle, which leads to increased urination and thus can deplete potassium levels, as potassium is also lost in urine. Patients with hypokalemia might require potassium supplementation, and in emergency cases, intravenous (IV) potassium (KCl) may be administered to rapidly increase potassium levels. Furthermore, loop diuretics are commonly prescribed to treat hypertension because they reduce fluid volume in the body, which helps lower blood pressure.