Losartan

is prescribed to treat:

• High blood pressure (hypertension) • Diabetic nephropathy (kidney disease in type 2 diabetics with high blood pressure) • Reduce the risk of stroke in patients with high blood pressure and left ventricular hypertrophy • Heart failure (sometimes used as alternative to ACE inhibitors) • Chronic kidney disease

It helps protect organs from damage caused by high blood pressure.

Losartan (Cozaar) is an angiotensin II receptor blocker used for high blood pressure, for kidney protection in diabetic nephropathy, and to reduce stroke risk in patients with hypertension and left ventricular hypertrophy. It was the first ARB brought to market, and it remains widely used because it delivers most of the benefit of an ACE inhibitor without the cough that drives roughly one in ten patients off that class.

Mechanism of Action

Losartan blocks the angiotensin II type 1 receptor directly, rather than blocking the enzyme that produces angiotensin II. The downstream consequences are similar to ACE inhibition — less arterial vasoconstriction, less aldosterone release, less sodium and water retention, and reduced pressure inside the glomerulus — but the route there differs in one clinically decisive way.

Because ARBs act at the receptor, they leave angiotensin-converting enzyme untouched, and therefore do not raise bradykinin. Bradykinin accumulation is what produces the ACE inhibitor cough and contributes to angioedema, so ARBs largely avoid both. Angioedema still occurs on ARBs, but far less often, which is why a patient who had angioedema on an ACE inhibitor is switched only with caution and explicit counselling rather than routinely.

Losartan has a second property unique in its class: it is mildly uricosuric, meaning it increases uric acid excretion and lowers serum uric acid. That makes it a rational antihypertensive choice in a patient who also has gout, particularly one whose gout was worsened by a thiazide diuretic. The effect is modest and does not substitute for urate-lowering therapy with allopurinol, but it is a genuine tiebreaker.

Losartan is a prodrug converted by CYP2C9 to a more potent active metabolite, and its parent-drug half-life is short. This is why losartan is sometimes dosed twice daily where other ARBs are comfortably once-daily, and why blood pressure control that fades before the next dose is worth checking for.

Clinical Use

Losartan is a first-line antihypertensive, the standard substitute when an ACE inhibitor causes cough, and a strong choice in chronic kidney disease with proteinuria, where reducing intraglomerular pressure slows progression. It is used in congestive heart failure when an ACE inhibitor is not tolerated, and in patients with left ventricular hypertrophy it reduced stroke more than atenolol in the LIFE trial.

As with ACE inhibitors, response is somewhat lower as monotherapy in Black patients and older adults, whose hypertension tends to be more volume-dependent. Combination with amlodipine or hydrochlorothiazide works well and is available as a single pill, which measurably improves adherence in a condition that produces no symptoms to remind patients why they are treating it.

Combining an ARB with an ACE inhibitor such as lisinopril is not recommended. Dual blockade of the same axis raises hyperkalemia and acute kidney injury without improving outcomes. The American Heart Association sets out how the classes compare, and the blood pressure numbers article explains the targets patients are being treated toward.

Monitoring and Follow-Up

Check creatinine, eGFR, and potassium before starting and again one to two weeks after initiation or a dose increase. As with ACE inhibitors, a creatinine rise of up to roughly 30 percent that then plateaus is expected and reflects the intended reduction in glomerular pressure rather than injury; a larger or continuing rise warrants investigation for volume depletion or renal artery stenosis.

Hyperkalemia is the other monitoring priority, and risk climbs with reduced kidney function, diabetes, potassium supplements, potassium-sparing diuretics, and salt substitutes — which are potassium chloride and are a frequently missed contributor. Once stable, potassium and kidney function are checked every six to twelve months.

Home readings give a far better picture of control than isolated office measurements, and the home monitoring guide covers the technique that makes them reliable. Our cardiovascular team reviews readings alongside total cardiovascular risk rather than in isolation. The MedlinePlus losartan entry carries the full prescribing detail.

Special Populations

Losartan is contraindicated in pregnancy. Like ACE inhibitors, ARBs cause fetal kidney injury, oligohydramnios, and skull hypoplasia, particularly in the second and third trimesters, and must be stopped as soon as pregnancy is recognised or planned. Women of reproductive age should be told this explicitly before starting.

In older adults losartan is well tolerated, but kidney function declines with age even when creatinine appears normal, so eGFR should guide decisions. Volume-depleted patients — those on high-dose diuretics or with poor oral intake — can drop their pressure sharply after the first dose, so correcting volume first is worthwhile. Hepatic impairment reduces conversion to the active metabolite and warrants a lower starting dose. Bilateral renal artery stenosis is a contraindication, since those kidneys depend on angiotensin II to maintain filtration.

One practical note on formulation: losartan is frequently dispensed as a fixed-dose combination with hydrochlorothiazide, and patients often do not realise they are taking two drugs. This matters when electrolyte problems appear, when a diuretic needs to be held during an illness with vomiting or diarrhea, and when a second prescriber adds another diuretic without knowing one is already on board. Reading the full name on the bottle rather than the shorthand on a medication list is a small habit that prevents a recurring category of error.

When to Contact Your Doctor

Swelling of the lips, tongue, face, or throat, or any difficulty breathing or swallowing, needs emergency care — angioedema is rarer on ARBs than on ACE inhibitors but is not impossible. Report muscle weakness, palpitations, or an irregular heartbeat, which can signal high potassium and warrant prompt lab work. Lightheadedness on standing suggests the dose is too high or that you are volume depleted. Reduced urine output or new swelling should be reported. Tell your clinician before starting NSAIDs, which blunt the blood pressure effect and raise kidney risk when combined with an ARB and a diuretic.

To review your blood pressure control, kidney function, and whether your regimen still matches your risk, contact us or schedule a visit.