Angiotensin II Receptor Blockers (ARBs)
Key Points
- ARBs block angiotensin II (AT1) receptors → prevent vasoconstriction and aldosterone release → lower blood pressure and reduce cardiac afterload.
- Preferred over ACE inhibitors when ACE inhibitor-induced cough occurs; similar efficacy with better tolerability.
- Absolutely contraindicated in pregnancy — teratogenic effects on fetal kidneys in all trimesters.
- Monitor for hyperkalemia and renal function; avoid concurrent use of potassium-sparing diuretics or potassium supplements without monitoring.
Pathophysiology
Angiotensin II, a potent vasoconstrictor, acts on AT1 receptors in blood vessels, adrenal glands, and kidneys. Blocking these receptors:
- Prevents vasoconstriction → vasodilation → reduced peripheral resistance
- Inhibits aldosterone release → reduced sodium/water retention
- Reduces ventricular remodeling in heart failure
Unlike ACE inhibitors, ARBs do not inhibit bradykinin degradation — explaining the absence of ACE inhibitor-associated dry cough.
Common ARBs
| Drug | Typical Dose | Notes |
|---|---|---|
| Losartan (Cozaar) | 25–100 mg orally once daily | Prodrug; also lowers uric acid |
| Valsartan (Diovan) | 80–320 mg orally once daily | Heart failure indication |
| Candesartan (Atacand) | 16–32 mg orally daily | 1–2 divided doses |
| Telmisartan (Micardis) | 40–80 mg orally daily | Long half-life; also has PPAR-γ agonism |
Nursing Assessment
NCLEX Focus
ARBs are teratogenic — confirm contraception and verify not pregnant before prescribing to females of childbearing age. Monitor serum potassium and creatinine at baseline and periodically.
- Confirm pregnancy status before initiating — absolute contraindication; document counseling.
- Assess baseline electrolytes (especially potassium), BUN, creatinine, and blood pressure.
- Assess for concurrent use of potassium-sparing diuretics, potassium supplements, or NSAIDs.
- Assess for history of angioedema to any ARB or ACE inhibitor; cross-reactivity is possible.
- Patients with bilateral renal artery stenosis: ARBs may precipitate acute kidney injury.
Nursing Interventions
- Administer at the same time each day; may be taken with or without food.
- Monitor blood pressure before and after dose changes; initiate at low dose in elderly or hepatic impairment patients.
- Teach patients to rise slowly from sitting/lying to avoid orthostatic hypotension.
- Advise patients to avoid potassium salt substitutes and high-potassium foods in excess (potassium-sparing effect).
- Monitor for mood disorders and suicidal ideation — renin-angiotensin system is associated with mood disturbance risk.
Pregnancy Category X
ARBs are absolutely contraindicated in pregnancy. Use during the second and third trimesters causes fetal renal dysgenesis, oligohydramnios, skull hypoplasia, and neonatal death. Female patients of reproductive age must use effective contraception.
Hyperkalemia Risk
ARBs reduce aldosterone → decrease potassium excretion → elevated serum potassium. Combination with potassium-sparing diuretics, ACE inhibitors, or NSAIDs markedly increases hyperkalemia risk. Target serum potassium: 3.5–5.0 mEq/L.
Clinical Judgment Application
Clinical Scenario
A patient with hypertension and type 2 diabetes is switched from an ACE inhibitor to losartan after developing persistent dry cough.
- Recognize Cues: ACE inhibitor cough — bradykinin accumulation; switching to ARB is appropriate.
- Analyze Cues: ARBs provide equivalent antihypertensive/renoprotective effect without bradykinin effect.
- Prioritize Hypotheses: Verify no other causes of cough; ensure patient understands dosing and monitoring.
- Generate Solutions: Educate patient on potassium monitoring, pregnancy precautions, and signs of angioedema.
- Take Action: Initiate losartan per order; schedule follow-up potassium and creatinine in 2–4 weeks.
- Evaluate Outcomes: Blood pressure controlled; cough resolved; labs within normal limits.
Related Concepts
- antihypertensives - Broader antihypertensive drug class context.
- ace-inhibitors - Same RAAS pathway; ARBs preferred when ACE cough occurs.
- diuretics - Commonly combined with ARBs for additive BP control.
- heart-failure - Valsartan and candesartan indicated for HFrEF.
- kidney-disease - Renoprotective indication in diabetic nephropathy.
Self-Check
- Why do ARBs not cause the dry cough that ACE inhibitors do?
- What is the absolute contraindication for ARBs, and in which patient population must this always be addressed?
- Which electrolyte requires close monitoring with ARB therapy, and why?