ARB

Angiotensin II Receptor Blockers (ARBs) are a class of antihypertensive drugs used primarily for the treatment of hypertension and heart failure. They function by blocking the effects of angiotensin II, a potent vasoconstrictor, at the angiotensin II type 1 (AT1) receptors on blood vessels and in the adrenal gland. This action leads to vasodilation, reduced secretion of vasopressin, and decreased production and secretion of aldosterone, thereby lowering blood pressure.

Mechanism of Action

ARBs selectively block the binding of angiotensin II to the AT1 receptor. Unlike ACE inhibitors, which prevent the formation of angiotensin II, ARBs do not affect the breakdown of bradykinin, a process that can lead to the cough side effect associated with ACE inhibitors. By blocking the AT1 receptor, ARBs prevent angiotensin II from exerting its vasoconstrictive and aldosterone-secreting effects, leading to decreased blood pressure.

Indications

ARBs are primarily indicated for the treatment of:

• Hypertension - They are often used when patients experience side effects from ACE inhibitors.
• Heart failure - ARBs can be used in patients intolerant to ACE inhibitors.
• Diabetic nephropathy - They provide renal protection in patients with type 2 diabetes.
• Chronic kidney disease (CKD) - ARBs can slow the progression of CKD.

Common ARBs

Some of the commonly prescribed ARBs include:

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

Side Effects

While generally well-tolerated, ARBs can cause some side effects, including:

• Dizziness
• Hyperkalemia (high potassium levels)
• Renal impairment
• Rarely, angioedema (swelling similar to hives but under the skin)

Comparison with ACE Inhibitors

ARBs and ACE inhibitors are both used to treat high blood pressure and heart failure. However, ARBs are often preferred for patients who experience a persistent cough as a side effect of ACE inhibitors. Additionally, ARBs have a lower incidence of angioedema compared to ACE inhibitors.

Contraindications

ARBs should not be used in patients with:

• History of angioedema related to previous ARB therapy
• Pregnancy
• Severe renal impairment (caution is advised)

Future Directions

Research continues into the development of newer ARBs with longer half-lives, improved efficacy, and fewer side effects. Studies are also exploring the potential benefits of ARBs in other conditions, such as migraine and certain types of cancer.