Irbesartan

Irbesartan is an angiotensin II receptor antagonist (ARB, also called an angiotensin II receptor blocker or sartans group) used for the treatment of hypertension (high blood pressure) and for the treatment of kidney disease in patients with type 2 diabetes and hypertension (diabetic nephropathy). It selectively blocks the AT1 receptor, preventing the vasoconstrictive and sodium-retaining effects of angiotensin II.

Mechanism of Action

Irbesartan works by blocking the binding of angiotensin II to the AT1 receptor in vascular smooth muscle and the adrenal gland. This prevents angiotensin II from causing vasoconstriction and aldosterone secretion, resulting in vasodilation and reduced blood pressure. Unlike ACE inhibitors, ARBs do not inhibit bradykinin breakdown, which means they are much less likely to cause the persistent dry cough that is a common side effect of ACE inhibitors.

Diabetic Nephropathy

Irbesartan has specific evidence for slowing the progression of diabetic kidney disease in hypertensive patients with type 2 diabetes, as demonstrated in the large IDNT trial. It reduces proteinuria and slows the decline of glomerular filtration rate, making it a preferred choice for this patient population.

How to Take Irbesartan

Take irbesartan once daily, at the same time each day, with or without food. Swallow tablets whole with water. The usual starting dose for high blood pressure is 150 mg once daily, which may be increased to 300 mg once daily if blood pressure is not adequately controlled after several weeks.

Diabetic Nephropathy

For patients with type 2 diabetes and kidney disease, the recommended dose is 300 mg once daily. Blood pressure, kidney function (eGFR), and potassium levels should be monitored at the start and periodically throughout treatment, as irbesartan can raise potassium levels.

Irbesartan tablets are available in 75 mg, 150 mg, and 300 mg strengths. For hypertension: start at 150 mg once daily, maximum 300 mg daily. For diabetic nephropathy: 300 mg once daily. A combination tablet with hydrochlorothiazide (Co-Aprovel/Ifirmacombi) is also available. Store below 30°C.

Common Side Effects

Irbesartan is generally well tolerated. Dizziness (particularly on standing), headache, and fatigue are the most frequently reported side effects, especially at the start of treatment. Musculoskeletal symptoms, nausea, and flushing have also been reported. Unlike ACE inhibitors, irbesartan does not cause a dry cough, which is an advantage for patients who are intolerant of ACE inhibitors for this reason.

Important: Hyperkalaemia and Renal Function

Hyperkalaemia (elevated potassium levels) can occur, particularly in patients with renal impairment, diabetes, or those taking potassium supplements or potassium-sparing diuretics. Symptoms include muscle weakness, palpitations, and fatigue. Regular monitoring of electrolytes and kidney function is required. In rare cases, ARBs can cause acute kidney injury, especially with concurrent dehydration, NSAIDs, or contrast dye.

Irbesartan must not be used during pregnancy (all trimesters) due to serious risk of fetal harm including oligohydramnios, fetal renal dysfunction, skull hypoplasia, and fetal death. Women of childbearing potential must use effective contraception. ACE inhibitors and ARBs must not be combined. Avoid concurrent use of aliskiren in patients with diabetes or renal impairment. Use with caution in patients with bilateral renal artery stenosis, aortic or mitral valve stenosis, hypertrophic cardiomyopathy, or primary hyperaldosteronism.

Contraindicated in pregnancy. Contraindicated in patients with known hypersensitivity to irbesartan or any excipient. The combination of irbesartan with aliskiren is contraindicated in patients with diabetes mellitus or renal impairment. Not recommended during breastfeeding.