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Losartan Potassium; Uses, Dosage, Side Effects, Interactions, Pregnancy

Losartan is the potassium salt form of losartan, a non-peptide angiotensin II antagonist with antihypertensive activity. Losartan potassium selectively and competitively blocks the binding of angiotensin II to the angiotensin I (AT1) receptor. Angiotensin II, formed from angiotensin I by angiotensin-converting enzyme (ACE), stimulates the adrenal cortex to synthesize and secrete aldosterone, which decreases the excretion of sodium and increases the excretion of potassium. Angiotensin II also acts as a vasoconstrictor in vascular smooth muscle. Losartan potassium, by blocking the binding of angiotensin II to the AT 1 receptor, promotes vasodilatation and decreases the effects of aldosterone.

Losartan is an angiotensin-receptor blocker (ARB) that may be used alone or with other agents to treat hypertension. Losartan and its longer acting metabolite, E-3174, lower blood pressure by antagonizing the renin-angiotensin-aldosterone system (RAAS); they compete with angiotensin II for binding to the type-1 angiotensin II receptor (AT1) subtype and prevents the blood pressure increasing effects of angiotensin II.It works by relaxing blood vessels so that blood can flow more easily. Unlike angiotensin-converting enzyme (ACE) inhibitors, ARBs do not have the adverse effect of dry cough.

Mechanism of Action of Losartan

Losartan competitively inhibits the binding of angiotensin II to AT1 in many tissues including vascular smooth muscle and the adrenal glands. Losartan is metabolized to its active metabolite, E-3174, which is 10 to 40 times more potent than losartan and acts as a non-competitive AT1 antagonist. Inhibition of angiotensin II binding to AT1 inhibits its AT1-mediated vasoconstrictive and aldosterone-secreting effects and results in decreased vascular resistance and blood pressure. Losartan is 1,000 times more selective for AT1 than AT2. Inhibition of aldosterone secretion may increase sodium and water excretion while decreasing potassium excretion. Losartan is effective for reducing blood pressure and may be used to treat essential hypertension, left ventricular hypertrophy and diabetic nephropathy.

Angiotensin II (formed from angiotensin I in a reaction catalyzed by angiotensin converting enzyme (ACE, kininase II)), is a potent vasoconstrictor, the primary vasoactive hormone of the renin-angiotensin system and an important component in the pathophysiology of hypertension. It also stimulates aldosterone secretion by the adrenal cortex. Losartan and its principal active metabolite block the vasoconstrictor and aldosterone-secreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor found in many tissues, (e.g., vascular smooth muscle, adrenal gland). There is also an AT2 receptor found in many tissues but it is not known to be associated with cardiovascular homeostasis. Both losartan and its principal active metabolite do not exhibit any partial agonist activity at the AT1 receptor and have much greater affinity (about 1000-fold) for the AT1 receptor than for the AT2 receptor. In vitro binding studies indicate that losartan is a reversible, competitive inhibitor of the AT1 receptor. The active metabolite is 10 to 40 times more potent by weight than losartan and appears to be a reversible, non-competitive inhibitor of the AT1 receptor. Neither losartan nor its active metabolite inhibits ACE (kininase II, the enzyme that converts angiotensin I to angiotensin II and degrades bradykinin); nor do they bind to or block other hormone receptors or ion channels known to be important in cardiovascular regulation.

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Indications of Losartan

High Blood Pressure
Diabetic Kidney Disease
Diabetic Nephropathies
Heart Failure,
Hypertension
Marfan Syndrome
Strokes
Treatment of uncomplicated hypertension,
Isolated systolic hypertension and left ventricular hypertrophy.
Delay or progression of diabetic nephropathy.
Second line agent in the treatment of congestive heart failure,
Systolic dysfunction,
Myocardial infarction and coronary artery disease in those intolerant of ACE inhibitors
Risk of stroke in patients with hypertension and left ventricular hypertrophy.
Diabetic nephropathy with an elevated serum creatinine and proteinuria
May be used as a first line agent to treat uncomplicated hypertension, isolated systolic hypertension and left ventricular hypertrophy. May be used as a first line agent to delay progression of diabetic nephropathy.
Losartan may be also used as a second line agent in the treatment of congestive heart failure, systolic dysfunction, myocardial infarction and coronary artery disease in those intolerant of ACE inhibitors.

Therapeutic Indications of Losartan

Angiotensin II Type 1 Receptor Blockers; Anti-Arrhythmia Agents; Antihypertensive Agents
Losartan is indicated for the treatment of hypertension. It may be used alone or in combination with other antihypertensive agents, including diuretics.
Losartanis indicated to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy, but there is evidence that this benefit does not apply to Black patients
Losartan is indicated for the treatment of diabetic nephropathy with an elevated serum creatinine and proteinuria (urinary albumin to creatinine ratio =300 mg/g) in patients with type 2 diabetes and a history of hypertension. In this population,
Losartan reduces the rate of progression of nephropathy as measured by the occurrence of doubling of serum creatinine or end stage renal disease (need for dialysis or renal transplantation)
Angiotensin II receptor antagonists including losartan have been used in the management of congestive heart failure

Contra indications of Losartan

Extreme loss of body water
High amount of potassium in the blood
Renal artery stenosis
Abnormally low blood pressure
Liver problems
Blockage of a bile duct
Kidney disease with reduction in kidney function
Pregnancy
Decreased Blood Volume
Second and third trimester of pregnancy
Biliary obstructive disorders.
Severe hepatic impairment.
Hypersensitivity to the active substance or to any of the excipients
Pregnancy
Decreased blood volume
Allergies to losartan & ARB-Angiotensin Receptor Antagonist

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Dosage of Losartan

Strengths: 25 mg, 50 mg, 100 mg

The typical starting dosage is 50 mg once daily. Dosages range between 25 and 100 mg per day. You take losartan once or twice per day.

Hypertension

Initial dose: 50 mg orally once a day
Maximum dose: 100 mg orally once a day

Diabetic Nephropathy

Initial dose: 50 mg orally once a day
Maximum dose: 100 mg orally once a day

Pediatric Dose for Hypertension

6 Years or Older

Initial dose: 0.7 mg/kg orally once a day (up to 50 mg total)

Side Effects of Losartan

The most common

Common

chills or fever
a headache, severe and throbbing
joint or back pain
muscle aching or cramping
muscle pains or stiffness
chest pressure or squeezing pain in the chest
excessive sweating
sudden drowsiness or need to sleep
coughing up blood
liver problems–nausea, upper stomach pain, itching, tired feeling, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes)
decreased amount of urine

Rare

Anxiety
change in vision
chest pain or tightness
confusion
a cough
Agitation
arm, back, or jaw pain
blurred vision
chest pain or discomfort
convulsions
extra heartbeats
hallucinations
a headache
irritability
lightheadedness
cold and clammy skin
fast and shallow breathing
swelling of your feet, legs, or hands purple spot on your skin caused by internal bleeding
fast or abnormal heart rate or palpitations
loss of appetite
lower back, side, or stomach pain
mental depression
muscle pain or cramps
Swelling of your feet or ankles
Shortness of breath
Nausea, fever, dark urine, loss of appetite
Depression

Drug Interactions of Losartan

Losartan may interact with following drugs, supplements, & may change the efficacy of drugs

alpha blockers (e.g., alfuzosin, doxazosin, tamsulosin)
angiotensin-converting enzyme inhibitors (ACEIs; captopril, enalapril, ramipril)
“azole” antifungal medications (e.g., fluconazole, itraconazole, ketoconazole)
barbiturates (e.g., butalbital, pentobarbital, phenobarbital)
benzodiazepines (e.g., clonazepam, diazepam, lorazepam)
beta-blockers (e.g., atenolol, metoprolol, propranolol)
calcium channel blockers (e.g., amlodipine, diltiazem, nifedipine, verapamil)
carbamazepine
cimetidine
clopidogrel
cyclosporine
dasatinib
dexamethasone
canagliflozin
diuretics (water pills; e.g., furosemide, hydrochlorothiazide, )
duloxetine
asthma medications (e.g., theophylline)
diltiazem
nitroglycerin
nonsteroidal anti-inflammatory medications (NSAIDs; e.g., indomethacin, naproxen)
oral diabetes medications (e.g., metformin, pioglitazone)
pentoxifylline
monoamine oxidase (MAO) inhibitors (e.g., phenelzine, selegiline, )
heparin and low-molecular-weight heparins
medications that increase the level of potassium in the blood (e.g., spironolactone,)
non-steroidal anti-inflammatory medications (NSAIDs; e.g., diclofenac, ibuprofen, naproxen)
pentoxifylline
phenytoin
phosphodiesterase 5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
rituximab
trimethoprim

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Pregnancy & Lactation of Losartan

FDA Pregnancy Category D

Pregnancy

Losartan should not be taken by pregnant women as it can cause harm to an unborn child. If you are planning to become pregnant, discuss alternative medications for blood pressure control with your doctor. If you become pregnant while taking this medication, stop taking it and tell your doctor at once.

Lactation

It is not known if losartan passes into breast milk. If the breastfeeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding. The safety and effectiveness of using this medication have not been established for children less than 6 years of age.