ARBs (Angiotensin Receptor Blockers)

What it is

ARBs are blood pressure medicines that block the angiotensin II type 1 receptor and are not safe in pregnancy. Angiotensin receptor blockers, also called angiotensin II receptor blockers, are a drug class used mainly for hypertension, heart failure, and chronic kidney disease, especially when kidney protection is needed. A key practical fact is that ARBs are contraindicated during pregnancy because drugs acting on the renin-angiotensin system can harm the fetus.

ARBs are often chosen when a person cannot tolerate an ACE inhibitor, especially because ACE inhibitors more commonly cause a dry cough. Common ARBs include losartan, valsartan, telmisartan, olmesartan, candesartan, and irbesartan. They lower blood pressure and can reduce protein loss in urine in some people with kidney disease, including diabetic kidney disease.

A quick comparison:

Feature	ARBs
Main target	Angiotensin II type 1 (AT1) receptor
Main uses	Hypertension, heart failure, chronic kidney disease
Common advantage vs ACE inhibitors	Less cough
Important risks	High potassium, low blood pressure, kidney function changes
Major contraindication	Pregnancy

In India, ARBs are widely used in routine hypertension care along with other first-line drug classes. Choice of medicine depends on blood pressure level, kidney function, diabetes status, heart disease, age, and cost.

How it works

ARBs block the action of angiotensin II at the AT1 receptor. Angiotensin II is part of the renin-angiotensin-aldosterone system, which helps regulate blood pressure, blood vessel tone, sodium balance, and fluid retention.

When angiotensin II binds to the AT1 receptor, it causes blood vessels to constrict and stimulates aldosterone release from the adrenal glands. Aldosterone makes the kidneys retain sodium and water and excrete potassium. By blocking this pathway, ARBs:

1. Relax blood vessels, which lowers blood pressure.
2. Reduce aldosterone effects, which can decrease sodium and water retention.
3. Lower pressure inside the kidney's filtering units, which may reduce albumin or protein in urine.
4. Reduce strain on the heart in some patients with heart failure.

Unlike ACE inhibitors, ARBs do not block the breakdown of bradykinin. That is one reason cough is generally less common with ARBs. However, ARBs can still cause serious adverse effects, including hyperkalemia and worsening kidney function in susceptible patients.

Evidence and uses

ARBs are established medicines with strong evidence for several cardiovascular and kidney-related uses. Their blood pressure-lowering effect is broadly comparable to other major antihypertensive classes, and they are commonly used alone or in combination with a calcium channel blocker or thiazide-type diuretic.

Main evidence-based uses include:

Condition	Role of ARBs
Hypertension	First-line option in many adults
Heart failure with reduced ejection fraction	Used in selected patients, especially if ACE inhibitors are not tolerated
Chronic kidney disease with albuminuria	Can reduce proteinuria and slow progression in some patients
Diabetic nephropathy	Often used when albuminuria is present

For hypertension, ARBs lower blood pressure effectively and are generally well tolerated. For chronic kidney disease, especially when albuminuria is present, they can help protect kidney function over time. For heart failure, some ARBs have outcome data supporting reduced hospitalization or symptom improvement in appropriate patients.

Not all ARBs are identical in approved indications, dosing schedules, or trial evidence. For example, losartan has uricosuric effects that may matter in some patients with gout, while telmisartan has a long half-life. These differences can influence prescribing, but the overall class effect remains similar for blood pressure control.

ARBs should not usually be combined with an ACE inhibitor or with the direct renin inhibitor aliskiren in many patients because dual blockade increases the risk of kidney injury, hypotension, and hyperkalemia without clear added benefit for most people.

Safety and interactions

ARBs are usually well tolerated, but they still require monitoring. The most important safety issues are high potassium, low blood pressure, and changes in kidney function.

Common or important adverse effects include:

• Dizziness or lightheadedness
• Low blood pressure, especially after starting treatment or increasing the dose
• Hyperkalemia
• Rise in serum creatinine or reduced kidney function
• Rare angioedema

People at higher risk of complications include those with chronic kidney disease, dehydration, older age, heart failure, bilateral renal artery stenosis, or those taking other medicines that raise potassium.

Important interactions include:

Interacting medicine or product	Why it matters
Potassium supplements or salt substitutes with potassium	Can raise potassium too much
Potassium-sparing diuretics such as spironolactone	Higher hyperkalemia risk
NSAIDs such as ibuprofen or diclofenac	Can worsen kidney function and blunt blood pressure control
Lithium	Lithium levels can rise
ACE inhibitors or aliskiren	Higher risk of kidney injury, hypotension, hyperkalemia

Patients should tell their clinician about over-the-counter pain medicines, supplements, and low-sodium salts, because many salt substitutes use potassium chloride. In India and elsewhere, this is an easy interaction to miss.

Pregnancy safety is a major issue. ARBs should be stopped and reviewed urgently if pregnancy occurs or is planned. People who are breastfeeding or trying to conceive should discuss alternatives with a clinician.

When to see a clinician

See a clinician promptly if you develop fainting, severe dizziness, swelling of the face or tongue, very low urine output, or symptoms that could suggest high potassium such as marked weakness or palpitations. Routine follow-up is also important after starting an ARB or increasing the dose.

Clinicians commonly check:

1. Blood pressure response
2. Serum creatinine or estimated kidney function
3. Serum potassium

These blood tests are often checked soon after starting therapy or after a dose change, then repeated based on the person's risk profile. Do not stop or double the medicine on your own unless a clinician tells you to, but seek advice if you have vomiting, diarrhea, dehydration, or an acute illness because temporary medicine review may be needed.

Limitations and open questions

ARBs are effective, but they are not the best choice for every patient. Some people need a different first-line drug or a combination regimen to reach blood pressure targets. Class members also differ in trial evidence, approved indications, and duration of action, so they are not perfectly interchangeable.

Evidence is strong for hypertension, selected heart failure settings, and kidney disease with albuminuria, but less certain for some proposed benefits beyond these uses. Reviews have discussed possible differences among individual ARBs, yet head-to-head superiority claims are often limited by study design and indirect comparisons.

Another limitation is that ARBs can initially raise creatinine, which may be expected in some cases but can also signal harm in others. That is why lab monitoring matters. For patients, the practical message is simple: ARBs are widely used and often well tolerated, but they should be taken under medical supervision, with attention to pregnancy risk, kidney function, potassium, and drug interactions.