Angiotensin receptor blockers (ARBs) pharmacology
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Mechanism of Action and Receptor Binding of Angiotensin Receptor Blockers (ARBs)
Angiotensin receptor blockers (ARBs) work by blocking the angiotensin II type 1 (AT1) receptor, which prevents the effects of angiotensin II, a hormone that causes blood vessels to constrict and raises blood pressure. ARBs differ in their binding characteristics; some are surmountable antagonists (their effects can be overcome by high levels of angiotensin II), while others are insurmountable (their effects persist even with high angiotensin II levels). This difference in binding can influence their clinical effects and potential benefits in various conditions. ARBs also allow angiotensin II to act on the AT2 receptor, which may have beneficial cardiovascular effects .
Clinical Uses and Efficacy in Hypertension and Cardiovascular Disease
ARBs are recommended as first-line therapy for hypertension in both US and European guidelines, alongside ACE inhibitors, calcium channel blockers, and thiazide diuretics. They are effective in lowering blood pressure and are generally as effective as ACE inhibitors in this regard. ARBs are also well-tolerated, with fewer side effects compared to ACE inhibitors, making them a preferred option for many patients 26. Beyond hypertension, ARBs are used in patients with heart failure, left ventricular hypertrophy, recurrent myocardial infarctions, and renal disease, especially when ACE inhibitors are not tolerated 16.
Protective Effects on Cardiovascular and Renal Systems
ARBs provide significant protection against cardiovascular and renal damage. They help reduce the risk of hypertensive-mediated organ damage and major adverse cardiovascular events. Unlike some other antihypertensive drugs, ARBs have a neutral effect on metabolism, which is beneficial for patients with metabolic syndrome or diabetes 26. However, while ARBs reduce the risk of stroke, heart failure, and diabetes, evidence suggests they do not significantly lower the risk of myocardial infarction, cardiovascular death, or all-cause mortality compared to placebo or other antihypertensive agents 810.
Pharmacogenetics and Individual Response to ARBs
The response to ARBs can vary significantly between individuals due to genetic differences. Pharmacogenetic studies indicate that genetic polymorphisms may influence how patients respond to ARB therapy. Understanding these genetic factors could help tailor antihypertensive treatment to individual patients, improving efficacy and reducing non-response rates .
Additional Pharmacological Properties and Emerging Uses
ARBs have shown neuroprotective effects in preclinical studies, reducing inflammation and neuronal injury in models of stroke, traumatic brain injury, and neurodegenerative diseases. Some ARBs may also activate peroxisome proliferator-activated receptor gamma (PPARγ), contributing to their beneficial effects beyond AT1 receptor blockade . There is also evidence that ARBs can influence angiogenesis, with anti-angiogenic effects in some disease models and pro-angiogenic effects in others, such as after myocardial infarction or stroke .
ARBs in Special Populations and COVID-19
ARBs are considered safe and beneficial for patients with comorbidities such as diabetes and renal disease, and their use should be continued during the COVID-19 pandemic. ARBs may protect the lungs and enhance the protective effects of ACE2, which is relevant in viral infections like COVID-19 72.
Drug Delivery and Patient Compliance
Traditional oral ARB formulations are subject to first-pass metabolism and variable absorption, which can affect bioavailability and patient compliance. Transdermal delivery systems for ARBs are being developed to improve bioavailability, reduce side effects, and enhance patient adherence to therapy .
Conclusion
ARBs are a cornerstone in the management of hypertension and have important roles in protecting cardiovascular and renal health. They are generally well-tolerated, effective, and have additional benefits in certain populations. Ongoing research into their pharmacogenetics, neuroprotective effects, and alternative delivery methods continues to expand their therapeutic potential.
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