12.01.4 β-Adrenoceptor Blockers for Hypertension
The third group of drugs commonly used in the treatment of hypertension are the β-adrenoceptor antagonists (β-blockers). On the heart, noradrenaline stimulates β1-adrenoceptors to increase heart rate and heart force, and on the kidney, noradrenaline stimulates β1-adrenoceptors to increase renin production, and hence angiotensin II and aldosterone production. Angiotensin II causes vasoconstriction and aldosterone causes salt and water retention, and both of these effects increase blood pressure. Thus, a β1-adrenoceptor antagonist e.g. atenolol will effectively decrease these effects to cause a decrease in heart rate and force, and a decrease in vasoconstriction and salt and water retention. The β1-adrenoceptor antagonist atenolol is commonly used in the treatment of essential hypertension. Atenolol is active after oral administration. Atenolol is hydrophilic, which means there is little penetration of central nervous system and no centrally mediated adverse effects, such as nightmares. Atenolol has an elimination t1/2 of 5-8 h, which allows once-a-day administration. Atenolol is excreted, largely unchanged, in urine, which means that a downward dosage adjustment may be needed in renal failure to prevent adverse effects.
The β-adrenoceptor blockers are contraindicated in subjects with asthma. These, and other details relating to β-adrenoceptor blockers, were discussed in detail in Chapter 7.