Losartan vs Valsartan

## Overview

Losartan and valsartan are both angiotensin II receptor blockers (ARBs) that block AT1 receptors, providing effects similar to ACE inhibitors (lowering BP, reducing aldosterone, protecting kidneys) without causing dry cough. Key differences exist in prodrug status, uricosuric effect, and HF outcome data.

## Mechanism of Action

Both competitively block AT1 (type 1 angiotensin II) receptors, preventing angiotensin II from binding and causing vasoconstriction and aldosterone release. Unlike ACE inhibitors, ARBs do not inhibit bradykinin degradation, so they rarely cause cough.

## Pharmacokinetics

Losartan is a prodrug partially converted by CYP2C9 to its active carboxylic acid metabolite E-3174, which is 10–40× more potent and has a half-life of ~6–9 h. Losartan itself has a half-life of ~2 h. Valsartan is not a prodrug; it is active as administered, with half-life ~6 h, and is primarily eliminated in feces (hepatic excretion).

## Unique Losartan Properties

Losartan has a unique uricosuric effect (inhibits renal URAT1 transporter), reducing serum uric acid by ~10–15%. This property makes it the preferred ARB in patients with hypertension and gout or hyperuricemia. Valsartan does not share this property.

## Clinical Evidence

Valsartan has strong HFrEF evidence from Val-HeFT (reduced hospitalizations) and ValSARTAN (in post-MI HF). VALIANT directly compared valsartan to captopril post-MI. Losartan is supported by LIFE (reduces CV events vs. atenolol in hypertensive LVH) and RENAAL (renoprotection in diabetic nephropathy).

## Key Takeaways

- Losartan: prodrug (CYP2C9 to E-3174), uricosuric, preferred in gout/hyperuricemia
- Valsartan: direct-acting, better HFrEF data, no uricosuric effect
- Both well-tolerated; neither causes cough (unlike ACEi)