Angiotensin II receptor blockers
Angiotensin II receptor blockers (ARBs) lower blood
pressure by blocking the vasoconstrictive effects of angiotensin II. Specific
ARBs have varying pharmacokinetic properties and
all are highly bound to plasma proteins.
ARBs act by interfering with the renin-angiotensin-aldosterone system.
Specifically, these drugs block the binding of angiotensin to the AT1
receptor. This prevents angiotensin II from exerting its vasoconstricting
properties and from promoting the excretion of aldosterone. Both of these
actions result in lowered blood pres-sure.
ARBs don’t inhibit the conversion of angiotensin I
to an-giotensin II, nor do they cause a breakdown in bradykinin (a va-sodilator).
ARBs may be used alone or in combination with other
drugs such as a diuretic. Valsartan may also be used as an alternative to an
ACE inhibitor or for the management of heart failure. Because irbesartan and
losartan protect the renal system, they’re often pre-scribed for patients with
type 2 diabetes. Losartan is also used to reduce the risk of stroke in
high-risk patients with hypertension and left ventricular hypertrophy. (See Adverse reactions to ARBs.)
ARBs can interact with other drugs in various ways.
§ When losartan is taken with fluconazole, an
increased blood lev-el of losartan may result, leading to hypotension.
§ NSAIDs reduce the antihypertensive effects of
§ Rifampin may increase metabolism of losartan
and decrease its antihypertensive effect.
§ Candesartan may increase blood levels of
lithium, leading to lithium toxicity.
§ When digoxin is taken with telmisartan, an
increased blood level of digoxin may occur, possibly leading to digoxin
§ Potassium supplements may increase the risk
of hyperkalemia when used with ARBs.