No, losartan is NOT an ACE inhibitor
Losartan is an angiotensin II receptor blocker (ARB), not an ACE inhibitor—these are two distinct drug classes that work at different points in the renin-angiotensin system. 1
Mechanism of Action Differences
ACE inhibitors block the angiotensin-converting enzyme (ACE), which prevents the conversion of angiotensin I to angiotensin II and also inhibits the breakdown of bradykinin. Examples include captopril, enalapril, lisinopril, and ramipril 2, 3.
Losartan (an ARB) works downstream by selectively blocking the AT1 receptor, preventing angiotensin II from binding to its receptor. Critically, losartan does NOT inhibit ACE and does not affect bradykinin metabolism 1. This fundamental difference explains why losartan causes significantly less cough than ACE inhibitors—the cough associated with ACE inhibitors is related to bradykinin accumulation 4, 1.
Clinical Positioning in Guidelines
Multiple major guidelines clearly distinguish these drug classes 2, 3, 5:
- ACE inhibitors remain first-line for heart failure with reduced ejection fraction (HFrEF) and are the preferred agents for renin-angiotensin system inhibition 3
- ARBs like losartan are recommended as alternatives for patients who cannot tolerate ACE inhibitors, particularly those who develop cough or angioedema 2, 3, 6
- Both drug classes are listed separately in treatment tables and have distinct dosing recommendations 2, 7
Key Clinical Distinctions
Cough incidence: Studies demonstrate losartan causes cough at rates similar to placebo (17-29%), while ACE inhibitors cause cough in 62-69% of patients with prior ACE inhibitor-induced cough 1. This makes ARBs the preferred choice when ACE inhibitor cough is intolerable 4.
Angioedema risk: While angioedema is much less frequent with ARBs than ACE inhibitors, cross-reactivity can occur. Extreme caution is advised when switching from an ACE inhibitor to an ARB in patients with prior angioedema 3, 6, 3.
Efficacy: In heart failure trials, losartan and other ARBs have demonstrated non-inferiority to ACE inhibitors for mortality and morbidity outcomes 8. However, ACE inhibitors maintain their position as first-choice therapy based on longer clinical experience and more extensive trial data 3.
The bottom line: Losartan belongs to a completely different drug class (ARBs) than ACE inhibitors, with a distinct mechanism of action, side effect profile, and clinical positioning in treatment algorithms.