💊 Angiotensin Receptor Blockers
Drug Class & Overview
Angiotensin Receptor Blockers (ARBs), also known as sartans, are a class of cardiovascular medications used primarily for hypertension and heart failure. They offer an alternative to ACE inhibitors, particularly for patients who develop an ACE inhibitor-induced cough.
Mechanism of Action
ARBs selectively block the binding of angiotensin II to the AT1 receptor, preventing its vasoconstrictive and aldosterone-stimulating effects. This leads to vasodilation, reduced sodium and water retention, and decreased blood pressure. Unlike ACE inhibitors, they do not affect bradykinin metabolism.
Key Indications
ARBs are indicated for the treatment of essential hypertension, especially in patients intolerant to ACE inhibitors due to cough. They are also used in heart failure with reduced ejection fraction, particularly when ACE inhibitors are not tolerated. Like ACE inhibitors, they have a role in diabetic nephropathy to slow disease progression and reduce proteinuria.
Contraindications
Absolute contraindications include a history of angioedema (though less common than with ACE inhibitors), bilateral renal artery stenosis, and pregnancy. Caution is advised in patients with severe aortic stenosis or hypertrophic obstructive cardiomyopathy. Avoid in patients with significant hyperkalaemia.
Adverse Effects
Adverse effects are generally similar to ACE inhibitors but with a lower incidence of cough. Common side effects include dizziness and hypotension, particularly first-dose hypotension. Hyperkalaemia and worsening renal function are important risks, especially in susceptible individuals. Angioedema is rare but can occur.
Monitoring
Baseline renal function (urea, creatinine, eGFR) and electrolytes (especially potassium) should be assessed before starting treatment. These should be re-checked within 1-2 weeks of initiation or dose adjustment, and then regularly (e.g., annually) or if the patient becomes unwell. Blood pressure monitoring is essential.
Prescribing Safety (OSCE)
Always check for previous allergic reactions or angioedema, though ARB-induced angioedema is less common. Be aware of interactions with NSAIDs (risk of acute kidney injury) and potassium-sparing diuretics (risk of hyperkalaemia). Counsel patients on potential side effects like dizziness and the importance of blood tests. Emphasise the contraindication in pregnancy.
MLA High-Yield Notes
Key points include their use as an alternative to ACE inhibitors for cough, their similar efficacy and side effect profile (minus the cough), and the contraindication in pregnancy. Understand their mechanism of action in blocking the AT1 receptor. Monitoring requirements are identical to ACE inhibitors.
Common SBA Themes
SBAs often focus on ARBs as an alternative for patients who develop an ACE inhibitor cough. Questions might present a patient with hyperkalaemia or declining renal function, asking about appropriate management. The contraindication in pregnancy is a recurring theme, as is the comparison of side effect profiles with ACE inhibitors.
References
- BNF (British National Formulary)
- NICE (National Institute for Health and Care Excellence)
- MHRA (Medicines and Healthcare products Regulatory Agency)