What is losartan, and how does it work (mechanism of action)?

Losartan is an oral medication that belongs to a class of drugs called angiotensin receptor blockers (ARBs). Other ARBs include irbesartan (Avapro), valsartan (Diovan), and candesartan (Atacand). Angiotensin formed in the blood by the action of angiotensin converting enzyme (ACE) is a powerful chemical that attaches to angiotensin receptors found in many tissues but primarily on smooth muscle cells of blood vessels. Angiotensin's attachment to the receptors causes the muscle cells to contract and the blood vessels to narrow (vasoconstrict) which leads to an increase in blood pressure (hypertension). Losartan (more specifically, the chemical formed when the liver converts the inactive losartan into its active form) blocks the angiotensin receptor. By blocking the action of angiotensin, losartan relaxes muscle cells and dilates blood vessels thereby reducing blood pressure.

Losartan was approved by the FDA in April 1995.

What brand names are available for losartan?

Cozaar

Is losartan available as a generic drug?

GENERIC AVAILABLE: Yes

Do I need a prescription for losartan?

Yes

What are the side effects of losartan?

Side effects reported included:

• Diarrhea
• Muscle cramps
• Dizziness
• Insomnia
• Nasal congestion

Losartan also may cause:

• A persistent cough
• An increase serum potassium (hyperkalemia)
• Impotence

Losartan may reduce kidney function in some patients and should not be used by patients who have bilateral renal artery stenosis (narrowing of both arteries going to the kidneys).

Rare cases of rhabdomyolysis (muscle breakdown) have been reported.

What is the dosage for losartan?

The starting dose of losartan for adults is 25-50 mg daily. The maximum dose is 100 mg daily. The total daily dose may be divided and administered two doses daily. Losartan may be given with or without food.

The starting dose of losartan for pediatric patients 6 years of age or older is 0.7 mg/kg up to 50 mg once daily. Doses more than 1.4 mg/kg or 100 mg daily have not been evaluated in pediatric patients.

Which drugs or supplements interact with losartan?

Losartan may increase levels of blood potassium (hyperkalemia), which can lead to serious heart problems (arrhythmias). Therefore, concomitant use of other drugs or substances that increase blood-such as potassium-sparing diuretics (for example, spironolactone [Aldactone], triamterene, and amiloride), potassium supplements, or salt substitutes containing potassium may lead to dangerous increases in serum potassium.

Combining losartan or other ARBs with nonsteroidal anti-inflammatory drugs (NSAIDs) in patients who are elderly, fluid-depleted (including those on diuretic therapy), or with poor kidney function may result in reduced kidney function, including kidney failure. These effects usually are reversible.

The antihypertensive effect of losartan may be reduced by aspirin and other NSAIDs such as:

• ibuprofen (Advil, Children's Advil/Motrin, Medipren, Motrin, Nuprin, PediaCare Fever, etc.),
• indomethacin (Indocin, Indocin-SR), and
• naproxen (Anaprox, Naprelan, Naprosyn, Aleve).

Combining ARBs, ACE inhibitors, or aliskiren (Tekturna) increases risk of hypotension (low blood pressure), hyperkalemia, and reduces kidney function compared to each drug used alone and there is no additional benefit on preventing end stage kidney disease or death.

Aliskiren and losartan should not be combined in patients with diabetes or with renal impairment.

Increases in blood lithium (Eskalith, Lithobid) levels and lithium toxicity have occurred when lithium and ARBa or hydrochlorothiazide were combined. Blood lithium levels should be monitored.

Is losartan safe to take if I'm pregnant or breastfeeding?

When used in the second or third trimester of pregnancy , ARBs can cause injury and even death to the fetus. Losartan should not be used during pregnancy. When pregnancy is first detected, losartan should be stopped.

It is not known whether losartan is excreted in breast milk, but losartan and its active form are excreted in rat milk. Due to the possibility of harm to the nursing infant, if possible, losartan should be discontinued by females who are nursing.

What else should I know about losartan?

What preparations of losartan are available?

Tablets: 25, 50 and 100 mg

How should I keep losartan stored?

Tablets should be stored at room temperature in a tightly closed, light resistant container.