ARBs — Clinical Use & Key Differences

A patient switched from lisinopril to losartan because of a persistent dry cough — but the blood pressure goal stays the same. What changed pharmacologically, and what didn't?

Angiotensin II receptor blockers (ARBs — losartan, valsartan, irbesartan, candesartan) block angiotensin II at the AT1 receptor rather than preventing its formation. This distinction matters: ACE inhibitors block the enzyme that converts angiotensin I to II, which also causes bradykinin to accumulate. ARBs skip that enzyme entirely, so bradykinin does not build up — which is why the dry cough and angioedema risk seen with ACE inhibitors are significantly reduced (though a small residual angioedema risk remains, especially in patients with prior ACE inhibitor-induced angioedema). Indications overlap heavily with ACE inhibitors: hypertension, heart failure with reduced ejection fraction, diabetic nephropathy (particularly losartan and irbesartan for type 2 diabetic nephropathy), and post-MI left ventricular dysfunction. ARBs are first-line alternatives when an ACE inhibitor is not tolerated. They are NOT combined with ACE inhibitors — dual RAAS blockade increases hyperkalemia, hypotension, and renal failure risk without added benefit. Like ACE inhibitors, ARBs are absolutely contraindicated in pregnancy (Category X equivalent — fetal renal damage and death, especially second and third trimesters). Potassium and renal function monitoring still applies because the downstream effect on aldosterone suppression is the same.

Key Distinctions

Don't confuse the mechanism: ACE inhibitors block the enzyme (bradykinin accumulates → cough); ARBs block the receptor (no bradykinin effect → no cough). Students assume ARBs are "safer" overall — they still carry hyperkalemia and renal risks identical to ACE inhibitors. Never combine an ARB with an ACE inhibitor; this is a common NCLEX distractor framed as "adding" therapy for refractory hypertension.

Clinical Pearl

ARBs are the 'no-cough cousin' of ACE inhibitors — same family reunion (RAAS blockade), same pregnancy ban, same potassium watch, just a different seat at the table.