Angiotensin Receptor Blockers (ARBs)

The class of drugs called angiotensin receptor blockers (ARBs), as the class name suggests, are drugs that block the action of angiotensin. Specifically, ARBs prevent angiotensin II from binding to the angiotensin II receptor on blood vessels and other tissues.

Angiotensin II is a very potent chemical that causes the muscles surrounding blood vessels to contract, thereby narrowing the blood vessels. Narrowing of blood vessels increases the pressure within the blood vessels and may lead to high blood pressure (hypertension). Reducing the binding and activity of angiotensin II leads to widening (dilation) of blood vessels and reduces blood pressure. By lowering blood pressure against which the heart must pump, the amount of work that the heart must do is reduced. ACE inhibitors also reduce blood pressure in the kidneys, slowing the progression of kidney disease due to high blood pressure or diabetes.

ARBs are used alone or in combination with other drugs for controlling high blood pressure. They also are used for treating congestive heart failure, preventing diabetes or high blood pressure-related kidney failure, and reducing the risk of stroke in patients with hypertension and an enlarged heart. ARBs also may prevent the recurrence of atrial fibrillation. Since ARBs have effects that are similar to those of ACE inhibitors, they are often used when ACE inhibitors are not tolerated by patients because of side effects.

ARBs are similar in action and side effects. They differ in how they are eliminated from the body and the extent to which they are distributed throughout the body.

• Some ARBs are converted to an active form in the body before they can exert their effects.
  
  
• Some ARBs are slightly better at reducing blood pressure than others; in some studies, irbesartan (Avapro) and candesartan (Atacand) were slightly more effective in reducing blood pressure than losartan (Cozaar).
  
  
• All ARBs usually are administered once daily for treatment of hypertension. Some patients may benefit from twice daily dosing of losartan (Cozaar) if blood pressure is not controlled with once daily dosing.

Common side effects include:

• dizziness,
• headache,
• drowsiness,
• nausea,
• vomiting,
• diarrhea,
• cough,
• elevated potassium levels,
• low blood pressure,
• muscle or bone pain, and
• rash.

ARBs cause cough less frequently than ACE inhibitors. Therefore, they are often substituted for ACE inhibitors when patients complain of cough with ACE inhibitors.

Like other antihypertensives, ARBs are associated with sexual dysfunction.

Serious, but rare, side effects include kidney failure, liver failure, allergic reactions, low white blood cells, and swelling of tissues (angioedema).

Individuals with stenosis (narrowing) of both arteries supplying the kidneys may experience worsening of kidney function.

Individuals who have experienced a severe reaction to an ARBs should not use other ARBs. ARBs usually are not prescribed for pregnant patients because they are associated with birth defects.

ARBs have few interactions with other drugs.

Fluconazole (Diflucan) impairs the conversion of losartan (Cozaar) to its active form, and rifamycin (Rifampin) reduces blood levels of losartan (Cozaar). Thus, both drugs may reduce the activity of losartan (Cozaar).

Combining ARBs with potassium supplements, salt substitutes (often contain potassium), or other drugs that increase potassium (for example, spironolactone), may result in excessive blood potassium levels (hyperkalemia) because ARBs also increase potassium levels. ARBs may also may increase the blood concentration of lithium (Eskalith) and lead to an increase in side effects from lithium (Eskalith).

Examples of ARBs include:

• candesartan (Atacand),
• eprosartan (Teveten),
• irbesartan (Avapro),
• losartan (Cozaar),
• olmesartan (Benicar),
• telmisartan (Micardis) and,
• valsartan (Diovan).

ARBs combined with hydrochlorothiazide or other antihypertensives are also available, for example:

• amlodipine and valsartan (Exforge),
• irbesartan-hydrochlorothiazide (Avalide),
• losartan potassium-hydrochlorothiazide (Hyzaar), and
• valsartan and hydrochlorothiazide (Diovan HCT).