McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 1 Adrenergic blocking antagonists

angina, migraine headaches) and to prevent reinfarc- tion after MI. These drugs are widely used and include nebivolol ( Nebilet ), oxprenolol ( Corbeton ) (not avail­ able in New Zealand), pindolol ( Visken ), propranolol ( Inderal ), sotalol ( Cardol, Sotacor ) and timolol ( Nyogel , Tenopt ). The prototype drug, propranolol, was the first non-selective beta blocker available. Therapeutic actions and indications The therapeutic effects of these drugs are related to their competitive blocking of the beta-adrenergic recep- tors in the SNS. The blockade of the beta-receptors in the heart and in the juxtaglomerular apparatus of the nephron accounts for the majority of the therapeutic benefit. Decreased heart rate, contractility and excita- bility, as well as a membrane-stabilising effect, lead to a decrease in arrhythmias, a decreased cardiac workload and decreased oxygen consumption. The juxtaglomer- ular cells are not stimulated to release renin, which further decreases the blood pressure. These effects are useful in treating hypertension and chronic angina and can help to prevent reinfarction after an MI by decreas- ing cardiac workload and oxygen consumption. Sotalol is used exclusively for treating life-threatening ven- tricular arrhythmias and to maintain sinus rhythm in individuals with atrial flutter or atrial fibrillation (see Chapter 45). Propranolol is very effective in blocking all of the beta-receptors in the SNS and was one of the first drugs of the class (see Table 31.4 for usual indications). Since the introduction of propranolol, newer and more select­ ive drugs have become available that are not associated with some of the adverse effects seen with total blockade of the SNS beta-receptors. Nebivolol is the newest adrenergic blocker available and is not associated with the variety of adverse effects seen with propranolol use. Oxprenolol blocks autonomic beta-adrenergic receptors leading to lowering of heart rate and reduces myocardial demand. Timolol has several recommended uses, which are listed in Table 31.4; timolol is available in an oph- thalmic form of the drug for reduction of intraocular pressure in people with open-angle glaucoma. When this drug is used topically, eye muscle relaxation occurs. In addition, because it is applied topically, it is usually not absorbed systemically from this route. Pharmacokinetics These drugs are absorbed from the GI tract after oral administration and undergo hepatic metabolism. Food has been found to increase the bioavailability of pro- pranolol, although this effect was not found with other beta-adrenergic blocking agents. Absorption of sotalol is decreased by the presence of food. Propranolol also crosses the blood–brain barrier, but nadolol and sotalol do not, making them a better choice if CNS effects

■■ Alpha 1 blood pressure by blocking the postsynaptic alpha 1 promoting vasodilation. ■■ Alpha 1 -selective adrenergic blocking agents are used to treat hypertension and are often used to treat BPH because of their relaxing effects on the bladder and prostate. NON-SELECTIVE BETA-ADRENERGIC BLOCKING AGENTS The beta-adrenergic blocking agents (Table 31.4) are used to treat cardiovascular problems (hypertension, indicate a need to adjust dose or discontinue the drug if cardiovascular effects are severe. ■ ■ Establish safety precautions if CNS effects or orthostatic hypotension occurs to prevent injury. ■ ■ Arrange for small, frequent meals if GI upset is severe to relieve discomfort and maintain nutrition. ■ ■ Arrange for supportive care and comfort measures (rest, environmental control, other measures) to decrease CNS effects ; provide headache medication to alleviate discomfort ; arrange safety measures if CNS effects occur to prevent injury. ■ ■ Offer support and encouragement to help the person deal with the drug regimen. ■ ■ Provide thorough teaching, including drug name, dosage and administration; measures to prevent adverse effects and warning signs to report to prescriber; safety measures such as changing positions slowly and avoiding driving or operating hazardous machinery, and dietary measures in conjunction with drug therapy to promote blood pressure control or alleviate GI upset to enhance knowledge about drug therapy and to promote compliance. ■ ■ Offer support and encouragement to help the person deal with the drug regimen. Evaluation ■ ■ Monitor response to the drug (lowering of blood pressure). ■ ■ Monitor for adverse effects (GI upset, CNS or cardiovascular changes). ■ ■ Evaluate effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for and specific measures to avoid them). ■ ■ Monitor the effectiveness of comfort measures and compliance with the regimen. -receptor sites, decreasing vascular tone and KEY POINTS -selective adrenergic blocking agents decrease