Losartan is a medicine used to treat high blood pressure, to protect the kidneys in diabetic patients with kidney disease, and in heart failure. It belongs to the angiotensin II receptor blocker (ARB) class and works by relaxing blood vessels, lowering blood pressure.
Also known as: Cozaar
Increased risk of hyperkalaemia. Both Losartan (ARB) and Spironolactone raise serum K+; the combination requires monitoring.
Losartan (ARB) reduces aldosterone production and spironolactone blocks its receptor — the effect on potassium is additive. The spironolactone label includes "angiotensin receptor blockers" in the list of "Agents Increasing Serum Potassium" (section 7.1) and recommends monitoring potassium when ACEi/ARB therapy is altered; the losartan label documents that "potassium-sparing diuretics, potassium supplements or salt substitutes may lead to increases in serum potassium" and warns of hyperkalaemia risk in patients with renal impairment or diabetes. Monitoring is essential: potassium and creatinine before initiation, 1 week after, 1 month after and then quarterly; do not use if K+ > 5,0 or creatinine clearance < 30 mL/min; stop potassium supplements and reduce spironolactone dose if K+ rises above 5,5.
Spironolactone + losartan: both spare potassium through complementary pathways. Monitor K+ and creatinine; avoid in CKD or high K+.
The ARB blocks the angiotensin II receptor (lower aldosterone) and Spironolactone blocks the aldosterone receptor — K+ retention via two pathways.
Serum K+ and renal function at week 1 and monthly.
Weakness, palpitations, irregular rhythm — possible signs of hyperkalaemia.
Start at low doses and check K+ and creatinine after 1 week.
DailyMed/FDA (NIH/NLM) — approved Losartan label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=df4f55f0-fb11-4f6f-a7ed-127b50f955fc ; approved Spironolactone label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=73564b3d-8ede-4008-b75c-1277153b5bb6
Losartan may raise serum potassium; potassium supplements or salt substitutes may cause hyperkalaemia.
Avoid potassium supplements and salt substitutes without supervision; monitor potassium in at-risk patients.
EMC-UK (MHRA) — approved Losartan SmPC: https://www.medicines.org.uk/emc/product/7783/smpc
Losartan is contraindicated in previous ARB-associated angioedema or hereditary angioedema.
Do not use in patients with a history of angioedema.
EMC-UK (MHRA) — approved Losartan SmPC: https://www.medicines.org.uk/emc/product/7783/smpc
Losartan is contraindicated in bilateral renal artery stenosis (or stenosis in a single functioning kidney) because of the risk of acute renal failure.
Do not use; assess renal function before starting an ARB.
EMC-UK (MHRA) — approved Losartan SmPC: https://www.medicines.org.uk/emc/product/7783/smpc
Losartan is contraindicated in pregnancy: ARBs may cause fetal renal injury, oligohydramnios and skull hypoplasia, especially in the 2nd and 3rd trimesters.
Do not start in pregnancy; if pregnancy is detected, stop losartan immediately.
Not recommended during breastfeeding; prefer an alternative with an established safety profile.
Women of childbearing age must use effective contraception during treatment.
EMC-UK (MHRA) — approved Losartan SmPC: https://www.medicines.org.uk/emc/product/7783/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Angiotensin II AT1 receptor antagonist (ARB), active mainly through the metabolite E-3174; used in hypertension, diabetic nephropathy and stroke risk reduction in left ventricular hypertrophy.
Selectively and competitively blocks angiotensin II AT1 receptors (vasoconstriction, sodium retention, cell proliferation, aldosterone), without affecting AT2 receptors; the active metabolite E-3174 (carboxylic acid) is responsible for most of the antagonism.
Well absorbed with substantial first-pass metabolism: systemic bioavailability ~33%; peak 1 h (losartan) and 3-4 h (metabolite); food slows absorption and reduces Cmax (AUC barely changed); high protein binding (free fractions 1.3% and 0.2%).
First-pass metabolism by CYP2C9 and CYP3A4: ~14% of the dose converted to the active metabolite E-3174, plus inactive metabolites; renal (~35%) and biliary/faecal (~60%) excretion of the drug and metabolites.
Terminal half-life ~2 h (losartan) and 6-9 h (active metabolite E-3174); total plasma clearance 600 mL/min (metabolite 50 mL/min).
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
