What are Angiotensin Receptor Blockers (ARBs)?

Angiotensin Receptor Blockers (ARBs)

Angiotensin Receptor Blockers (ARBs) are a class of medications that selectively block the binding of angiotensin II to type 1 angiotensin receptors, thereby inhibiting the renin-angiotensin-aldosterone system and reducing blood pressure, cardiovascular morbidity, and mortality. 1

Mechanism of Action

ARBs work by:

• Selectively blocking angiotensin II from binding to AT1 receptors
• Preventing vasoconstriction and reducing peripheral vascular resistance
• Decreasing aldosterone secretion, which reduces sodium and water retention
• Inhibiting cellular hypertrophy and remodeling in cardiovascular tissues 2

Unlike ACE inhibitors, ARBs:

• Do not inhibit kininase and therefore do not increase bradykinin levels
• Have a significantly lower incidence of cough and angioedema
• Provide more complete blockade of angiotensin II effects (including those produced through alternative enzyme pathways) 1

Clinical Applications

ARBs are indicated for:

1. Hypertension

   • Used as monotherapy or in combination with other antihypertensive agents
   • Effectively lower blood pressure by reducing peripheral vascular resistance 2, 3

2. Heart Failure with Reduced Ejection Fraction (HFrEF)

   • Recommended for patients with HFrEF who cannot tolerate ACE inhibitors
   • Reduce morbidity and mortality in heart failure patients 1

3. Diabetic Nephropathy

   • Slow the progression of diabetic kidney disease
   • Particularly effective in patients with albuminuria 3

4. Left Ventricular Hypertrophy

   • Reduce the risk of stroke in patients with hypertension and LVH 3

5. Post-Myocardial Infarction

   • Provide cardioprotection similar to ACE inhibitors in patients after MI 1

Available ARBs and Dosing

Common ARBs include:

• Losartan (25-100 mg once daily)
• Valsartan (20-160 mg twice daily)
• Candesartan (4-32 mg once daily)
• Irbesartan (150-300 mg once daily)
• Telmisartan (40-80 mg once daily)
• Eprosartan (400-800 mg once daily) 2

Safety and Adverse Effects

ARBs are generally well-tolerated with fewer side effects compared to many other antihypertensive medications:

• Common side effects: Dizziness, headache, upper respiratory infections, back pain, fatigue 4
• Serious but rare side effects: Hypotension, hyperkalemia, renal impairment 3
• Contraindications:
  • Pregnancy (Category D) - can cause fetal harm or death 3
  • Concurrent use with aliskiren in diabetic patients 3

Important Clinical Considerations

1. Monitoring requirements:

   • Renal function and serum potassium should be monitored, especially when initiating therapy
   • Blood pressure, including postural changes 2

2. Drug interactions:

   • Potassium supplements and potassium-sparing diuretics may increase risk of hyperkalemia
   • NSAIDs may reduce antihypertensive effect and increase risk of renal dysfunction
   • Dual blockade with ACE inhibitors generally not recommended due to increased adverse effects without significant additional benefits 3

3. Practical considerations:

   • ARBs are the preferred alternative for patients who develop cough with ACE inhibitors
   • Most ARBs can be taken with or without food (exception: valsartan bioavailability is reduced by food) 4
   • Once-daily dosing for most ARBs improves adherence 2

ARBs vs. ACE Inhibitors

• Both effectively reduce blood pressure and cardiovascular risk
• ARBs have lower incidence of cough and angioedema compared to ACE inhibitors
• ACE inhibitors are generally preferred as first-line therapy for HFrEF, with ARBs recommended for ACE inhibitor-intolerant patients 1
• Combination therapy with both ARBs and ACE inhibitors is generally not recommended due to increased risk of adverse effects without significant additional benefits 3

ARBs represent an important class of cardiovascular medications with proven benefits for reducing morbidity and mortality in various cardiovascular conditions, particularly in patients who cannot tolerate ACE inhibitors.