💊 ARBs for Hypertension: A Complete Guide to Angiotensin II Receptor Blockers

If you’ve been prescribed a blood pressure medication ending in “‑sartan” — such as losartan or telmisartan — you’re taking an ARB. ARBs (Angiotensin II Receptor Blockers) are one of the most commonly prescribed antihypertensives and are often preferred when a patient cannot tolerate an ACE inhibitor. Dr. Ravi Sishir Reddy explains exactly how ARBs work, why they’re used, and what you need to know about taking them safely.

1. What Are ARBs?

ARB stands for Angiotensin II Receptor Blocker. To understand how they work, recall that angiotensin II is a hormone that raises blood pressure by narrowing blood vessels and promoting sodium retention. ACE inhibitors block the formation of angiotensin II. ARBs take a different approach: they bind directly to the angiotensin II receptor (specifically the AT1 receptor) on blood vessels and other tissues, preventing angiotensin II from exerting its effects. The result is vasodilation, reduced aldosterone secretion, and lower blood pressure.

Commonly prescribed ARBs include:

• Losartan (Cozaar) — widely used, often the first ARB prescribed.
• Telmisartan (Micardis) — the longest‑acting ARB, effective for a full 24 hours.
• Valsartan (Diovan) — also used in heart failure.
• Irbesartan (Avapro) — commonly used in diabetic kidney disease.
• Candesartan (Atacand) — effective at low doses.
• Olmesartan (Benicar) — sometimes associated with a rare sprue‑like enteropathy.

2. How Do ARBs Lower Blood Pressure?

By blocking the AT1 receptor, ARBs prevent angiotensin II from binding. This has three major effects:

1. Vasodilation: Blood vessels relax and widen, reducing peripheral resistance.
2. Reduced aldosterone: The adrenal glands release less aldosterone, so the kidneys excrete more sodium and water, reducing blood volume.
3. Reduced sympathetic activity: ARBs dampen the sympathetic nervous system, contributing to lower heart rate and vascular tone.

ARBs also increase levels of angiotensin‑(1‑7), a protective peptide that further dilates vessels and reduces inflammation.

3. Why Are ARBs Prescribed?

Like ACE inhibitors, ARBs are more than just BP‑lowering drugs. They offer organ protection:

• Kidney protection: ARBs reduce proteinuria and slow the progression of diabetic and non‑diabetic kidney disease.
• Heart protection: They reverse left ventricular hypertrophy and improve survival in heart failure.
• Stroke prevention: Some studies suggest a slightly greater stroke‑reduction benefit with ARBs compared to other classes, independent of BP lowering.
• Better tolerance profile: They do not cause the dry cough associated with ACE inhibitors, making them a common alternative.

ARBs are often the first‑line choice in patients with hypertension and type 2 diabetes, chronic kidney disease, or those who cannot tolerate an ACE inhibitor due to cough.

4. Side Effects and Safety

ARBs are generally very well tolerated. The side effect profile overlaps with ACE inhibitors in some ways but is distinct in others:

• Dizziness: Especially when starting or increasing the dose, due to lowered BP.
• Elevated potassium (hyperkalemia): Because aldosterone is partially blocked. Monitoring of potassium levels is required, particularly in patients with kidney disease or those taking potassium supplements or potassium‑sparing diuretics.
• Fatigue: Mild, usually transient.
• Headache: Uncommon.
• Angioedema: Much rarer than with ACE inhibitors, but has been reported. If swelling of the lips, tongue, or airway occurs, the drug must be stopped and emergency care sought.

Note: ARBs do not cause the dry cough that ACE inhibitors do, because they do not increase bradykinin levels. This is the main advantage over ACE inhibitors.

5. Contraindications: Who Should Avoid ARBs?

ARBs are contraindicated in:

• Pregnancy: They can cause fetal kidney damage and skull defects. Women of childbearing age should use effective contraception, and the drug must be stopped immediately if pregnancy is detected.
• History of angioedema: Although rare, if a patient has had angioedema from any ARB or ACE inhibitor, ARBs should be avoided unless under specialist guidance.
• Bilateral renal artery stenosis: Similar to ACE inhibitors, ARBs can cause a precipitous drop in kidney function if both renal arteries are narrowed.
• Severe hyperkalemia: If potassium is already dangerously high.
• Combination with aliskiren (a direct renin inhibitor) in patients with diabetes or kidney impairment — this combination increases the risk of hyperkalemia and kidney injury.

6. Practical Tips for Taking ARBs

• Take once daily: Most ARBs are taken at the same time each day. Telmisartan, in particular, provides 24‑hour BP control.
• Monitor potassium and kidney function: Your doctor will check bloods within a few weeks of starting and periodically thereafter.
• Stand up slowly: To minimise dizziness from orthostatic hypotension, especially early in treatment.
• Avoid potassium salt substitutes unless approved by your doctor.
• Stay hydrated: As with any antihypertensive, dehydration can stress the kidneys.
• Report any facial swelling immediately: Although angioedema is rare with ARBs, it is a medical emergency.

7. ARBs vs. ACE Inhibitors: A Quick Comparison

Feature	ACE Inhibitors	ARBs
Mechanism	Block angiotensin II formation	Block angiotensin II receptor
Dry cough	Common (10‑20%)	Very rare
Angioedema risk	Higher	Lower, but possible
Organ protection	Excellent (kidney, heart)	Excellent (kidney, heart, stroke)
Pregnancy	Contraindicated	Contraindicated
Cost	Many generics available	Widely available generics

In practice, ARBs are often preferred when a patient develops a bothersome ACE inhibitor‑induced cough. Some guidelines also favour ARBs in stroke prevention, though both classes are effective. Dr. Reddy notes that the two classes are interchangeable in most situations, and the final choice depends on tolerability and cost.