Angiotensin II Receptor Blockers (ARBs) – Mechanism, Uses, Side Effects & Mnemonic

Angiotensin II Receptor Blockers (ARBs) are a vital class of antihypertensive medications that help manage high blood pressure, heart failure, and stroke prevention. They are often recognized by the suffix “-sartan”, with common examples including Losartan, Irbesartan, and Telmisartan.

These drugs work by blocking the actions of Angiotensin II, a potent vasoconstrictor in the Renin-Angiotensin-Aldosterone System (RAAS), thereby promoting relaxation of blood vessels and reducing blood pressure.

Let’s explore their classification, mechanism, clinical applications, side effects, and contraindications in a clear, student-friendly format.

Classification

Class	Category
Pharmacologic (P)	Angiotensin II Receptor Blockers (ARBs)
Therapeutic (T)	Antihypertensives

Common ARBs include:

• Losartan
• Irbesartan
• Telmisartan
• Valsartan
• Olmesartan
• Candesartan

All of these drugs end with the suffix “-sartan”, which makes them easy to identify in pharmacology.

Mechanism of Action (MOA)

ARBs block the binding of Angiotensin II to its receptors (mainly AT₁ receptors) found in vascular smooth muscle and adrenal glands.

As a result:

1. Vasoconstriction is inhibited, leading to vasodilation.

2. Aldosterone release decreases, reducing sodium and water reabsorption in the kidneys.

3. Blood volume and blood pressure fall.

This mechanism helps maintain hemodynamic stability and prevent excessive strain on the heart.

In simple terms, ARBs prevent Angiotensin II from tightening the blood vessels and increasing blood pressure.

Uses of Angiotensin II Receptor Blockers

ARBs are widely prescribed for cardiovascular and renal conditions:

1. Hypertension (High Blood Pressure) – First-line therapy for patients intolerant to ACE inhibitors.

2. Heart Failure – Reduces cardiac workload by lowering afterload and preload.

3. Stroke Prevention – Helps reduce recurrence risk in hypertensive individuals.

4. Diabetic Nephropathy – Protects kidney function by lowering intraglomerular pressure.

5. Chronic Kidney Disease (CKD) – Slows disease progression in hypertensive and diabetic patients.

Mnemonic to Remember ARB Adverse Effects – “FAIL”

ARBs ensure Angiotensin II effects FAIL, but they also come with potential side effects represented by the same mnemonic:

Letter	Meaning	Explanation
F	Fetal Injury	Can cause developmental harm to the fetus (especially in 2nd and 3rd trimesters).
A	Angioedema	Rare swelling of lips, face, or throat; similar to ACE inhibitor reaction.
I	Imbalance of Electrolytes	Can increase potassium (↑K⁺), reduce glucose (↓Glucose), and sodium (↓Na⁺).
L	Low Blood Pressure	Due to vasodilation and fluid loss.

Mnemonic meaning:

“The job of Sartans is to make sure the effects of Angiotensin II FAIL.”

 

Adverse Effects

Hypotension (Low BP) – Especially after the first dose in volume-depleted patients.

Hyperkalemia – Due to reduced aldosterone levels, potassium may accumulate.

Dizziness or Fatigue – From reduced vascular resistance.

Angioedema – Rare but potentially life-threatening.

Renal Impairment – In susceptible individuals with renal artery stenosis.

Drug Interactions

Drug	Interaction Effect
Lithium	Increases risk of lithium toxicity due to reduced renal clearance.
NSAIDs	Reduce the antihypertensive effect of ARBs by affecting renal prostaglandins.

Therefore, co-administration with these agents must be monitored carefully.

Contraindications

ARBs are contraindicated in:

1. Pregnancy – Can cause fetal toxicity and malformations (especially after the first trimester).

2. Severe Renal Impairment – May worsen kidney function in patients with bilateral renal artery stenosis.

3. Hypersensitivity – To any ARB component.

Black Box Warning

“Increased risk of fetal injury or death when used during pregnancy.”

Pregnant women or those planning pregnancy should avoid ARBs and consult their physician for safer alternatives.

Comparison: ARBs vs ACE Inhibitors

Feature	ARBs (e.g., Losartan)	ACE Inhibitors (e.g., Enalapril)
Mechanism	Block Angiotensin II receptors	Block conversion of Angiotensin I → II
Cough	Rare	Common (due to bradykinin accumulation)
Angioedema	Rare	More common
Preferred For	ACE inhibitor–intolerant patients	First-line hypertension management
Suffix	“–sartan”	“–pril”

Summary:

ARBs provide similar benefits to ACE inhibitors but with fewer side effects, especially the absence of a dry cough.

 

Clinical Pearls

• Always monitor serum potassium and creatinine levels during therapy.
• Avoid potassium supplements or potassium-sparing diuretics unless prescribed.
• ARBs are especially beneficial in diabetic patients due to renal protective effects.
• May be combined with thiazide diuretics for better blood pressure control.

Summary Table

Parameter	Details
Drug Class	Angiotensin II Receptor Blockers (ARBs)
Common Drugs	Losartan, Irbesartan, Telmisartan, Valsartan
Mechanism	Block Angiotensin II receptor → vasodilation + ↓Aldosterone
Uses	Hypertension, Heart Failure, Stroke prevention, Diabetic nephropathy
Mnemonic for Adverse Effects	FAIL – Fetal injury, Angioedema, Imbalance of electrolytes, Low BP
Interactions	Lithium (↑toxicity), NSAIDs (↓effect)
Contraindications	Pregnancy, Renal impairment
Black Box Warning	Fetal injury during pregnancy

FAQs About ARBs

Q1. What are Angiotensin II Receptor Blockers used for?

They are mainly used to treat hypertension, heart failure, and to protect the kidneys in diabetic patients.

Q2. How do ARBs differ from ACE inhibitors?

ARBs block the receptor of Angiotensin II, while ACE inhibitors block its formation. ARBs cause fewer side effects like cough.

Q3. Why should ARBs be avoided during pregnancy?

Because they can lead to fetal renal damage, low amniotic fluid, or even fetal death.

Q4. Do ARBs cause cough like ACE inhibitors?

No, ARBs do not cause cough because they do not increase bradykinin levels.

Q5. Which suffix helps identify ARBs?

All ARBs end with the suffix “-sartan”, such as Losartan, Telmisartan, and Irbesartan.