Review Question - QID 100601

Captopril is an ACE inhibitor; triamterene is a potassium-sparing diuretic. Both drugs can cause hyperkalemia.

ACE inhibitors can cause hyperkalemia by inhibiting aldosterone production. ACE inhibitors function to reduce blood pressure by stopping the conversion of angiotensin I to angiotensin II (a potent vasoconstrictor), thus impacting the renin-angiotensin-aldosterone axis. Aldosterone acts in the distal nephron to reabsorb sodium and excrete potassium. Inhibition of aldosterone, thus, results in increased Na+ excretion and K+ retention. ACE inhibitors most commonly cause hyperkalemia in renal insufficiency or in patients taking potassium-sparing diuretics (or potassium supplements).

In a letter to the editor of American Family Physician, Graves discusses some adverse effects of ACE inhibitors. Although rare, a potentially fatal complication of ACE inhibitor use is angioedema. This adverse effect is more common in African Americans, and anyone who takes this medication should be warned about this serious side-effect. Additionally, the use of NSAIDs while on an ACE inhibitor may also potentiate life-threatening hyperkalemia.

Parish et al. report on the adverse effects of ACE inhibitors. It has been shown that lower doses are effective in reducing the incidence of adverse reactions and ultimately result in improved patient tolerance. It was found that the most common adverse reactions of ACE inhibitors are cough and skin rash. Although hyperkalemia is still considered a frequent occurrence, when dietary potassium intake is appropriately regulated, hyperkalemia is seldom a serious problem.

Illustration A depicts an overview of the renin-angiotensin-aldosterone pathway. Illustration B depicts the mechanism of ACE inhibitors. Illustration C depicts the mechanism of triamterene (a potassium-sparing diuretic).

Incorrect Answers:
Answers 1,3-5: These answer choices would not be expected abnormalities of ACE inhibitor-potassium sparing diuretic combination therapy.