Losartan

Losartan occupies the AT1 receptor, where angiotensin II would otherwise act; that hormone narrows vessels and makes the kidneys retain salt. Vessels remain relaxed, blood pressure falls and the heart meets less resistance with each beat. ACE inhibitors act earlier in the same chain and frequently cause a dry cough; an angiotensin receptor blocker such as losartan seldom does, and that is the usual reason a doctor changes from one to the other.

The UK SmPC begins with essential hypertension, in adults and in children from the age of 6. Next comes protection of the kidneys in type 2 diabetes accompanied by high blood pressure and proteinuria. Third is chronic heart failure when an ACE inhibitor cannot be used. The fourth is a reduced risk of stroke in hypertensive adults with left ventricular hypertrophy, a thickened heart wall.

The 25 mg and 50 mg tablets are offered in 30, 60, 90, 120, 180 or 360, and the 100 mg tablet in 30, 60, 90, 120 or 180. Fifty milligrams once daily is where hypertension treatment starts and normally stays. The full effect takes three to six weeks to develop, and some patients move up to 100 mg, preferably as a morning dose. In diabetic kidney disease the start is also 50 mg, with 100 mg possible after a month if blood pressure permits. Heart failure needs a slower build-up: 12.5 mg once daily, then 25, 50 and 100 mg at weekly intervals, to a ceiling of 150 mg once daily if tolerated. A prescriber may start at 25 mg in patients who are dehydrated, perhaps after a strong diuretic, or over 75. A child of 20 to 50 kg receives 25 mg, and above 50 kg the dose is 50 mg. Food does not matter.

The second and third trimesters of pregnancy and severe liver impairment are contraindications, as is combining it with aliskiren in people with diabetes or an eGFR below 60. Women who are planning a pregnancy, or discover one while on treatment, should contact the prescriber straight away. Vomiting or diarrhoea can dehydrate the body and strain the kidneys, which is another reason to ring. Expect blood tests for kidney function and potassium early in treatment and whenever the dose is altered.

Potassium-sparing diuretics, potassium supplements, low-sodium salt substitutes, heparin and trimethoprim can push potassium too high. Anti-inflammatory painkillers may weaken the blood-pressure effect and burden the kidneys. Lithium levels can climb, and fluconazole and rifampicin change how losartan is handled by the body.

High blood pressure rarely announces itself, so it is tempting to skip tablets on days that feel normal. Doing so lets pressure creep up again, and the benefit depends on daily use, which is why treatment is usually long term. Useful questions for the prescriber are what target readings to aim for, whether home monitoring makes sense and when blood tests are due. Tell the prescriber about other medicines, over-the-counter anti-inflammatory painkillers, anything containing potassium and any pregnancy plans.

Tiredness, anaemia, dizziness and vertigo come up regularly, along with high potassium, low blood pressure and a fall in kidney function. A rare but urgent reaction is angioedema, in which the face, lips or throat swell. British law allows losartan to be supplied only on prescription. The licensed range includes Cozaar in 12.5, 25, 50 and 100 mg and generic losartan potassium from many companies, whereas the tablets on this page are imported. The prescriber alone decides if Losartan is started, altered or stopped.