McKenna's Pharmacology for Nursing, 2e

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

reinfarction after an MI by decreasing cardiac workload and oxygen consumption. Beta 1 -selective adrenergic blocking agents in oph- thalmic form are used to decrease intraocular pressure and to treat open-angle glaucoma. The beta 1 -selective blocker of choice depends on the condition or combina- tion of conditions being treated and personal experience with the drugs. See Table 31.5 for usual indications for each drug. -selective adrenergic blockers are absorbed from the GI tract after oral administration, reach peak levels directly with IV infusion and are not usually absorbed when given in ophthalmic form. The bio- availability of metoprolol is increased if it is taken in the presence of food. These drugs are metabolised in the liver and excreted in the urine. Metoprolol readily crosses the blood–brain barrier and may cause more CNS effects than atenolol, which does not cross the barrier. -selective adrenergic blockers are contrain- dicated in the presence of allergy to the drug or any components of the drug to avoid hypersensitivity reactions ; with sinus bradycardia, heart block, cardio- genic shock, HF or hypotension, all of which could be exacerbated by the cardiac-depressing and blood pressure-lowering effects of these drugs ; and with breastfeeding because of the potential adverse effects on the neonate. They should be used with caution in indi- viduals with diabetes, thyroid disease or COPD because of the potential for adverse effects on these diseases with sympathetic blockade ; and in pregnancy because of the potential for adverse effects on the fetus . The safety and efficacy of the use of these drugs in children have not been established. Adverse effects People receiving these drugs often experience adverse effects related to the blocking of beta 1 -receptors in the SNS. CNS effects include headache, fatigue, dizziness, depression, paraesthesias, sleep disturbances, memory loss and disorientation. CV effects can include brady­ cardia, heart block, HF, hypotension and peripheral vascular insufficiency. Pulmonary effects ranging from rhinitis to bronchospasm and dyspnoea can occur; these effects are not as likely to occur with these drugs as with the non-selective beta-blockers. GI upset, nausea, vomiting, diarrhoea, gastric pain and even colitis can occur as a result of unchecked parasympathetic activity and the blocking of the sympathetic receptors. Genitourinary effects can include decreased libido, Pharmacokinetics The beta 1 Contraindications and cautions The beta 1

impotence, dysuria and Peyronie’s disease. Other effects that can occur include decreased exercise tol- erance (people often report that their “get up and go” is gone), hypoglycaemia or hyperglycaemia, and liver changes that are reflected in increased concentrations of liver enzymes. If these drugs are stopped abruptly after long-term use, there is a risk of severe hyperten- sion, angina, MI and stroke because the receptor sites become hypersensitive to catecholamines after being blocked by the drug. Clinically important drug–drug interactions A decreased hypertensive effect occurs if these drugs are given with clonidine, NSAIDs, rifampicin or barbiturates. If such a combination is used, the person should be monitored closely and dose adjustment made. There is an initial hypertensive episode followed by bradycardia if these drugs are given with adrenaline. Increased serum levels and increased toxicity of intravenous lignocaine will occur if it is given with these drugs. An increased risk for orthostatic hypotension occurs if these drugs are taken with prazosin. If this combina- tion is used, the person must be monitored closely and safety precautions taken. The selective beta 1 -blockers have increased effects if they are taken with verapamil, cimetidine or propylth- iouracil. The person should be monitored closely and appropriate dose adjustment made. hypertension, myocardial infarction; off-label uses are prevention of migraine headaches, alcohol withdrawal syndrome and supraventricular tachycardias. Actions: Blocks beta 1 -adrenergic receptors, decreasing the excitability of the heart, cardiac output and oxygen consumption; decreases renin release, which lowers blood pressure. Pharmacokinetics: Route Onset Peak Duration Oral Varies 2–4 hours 24 hours IV Immediate 5 mins 24 hours T 1/2 : 6 to 7 hours, with excretion in the bile, faeces and urine. Adverse effects: Allergic reaction, dizziness, bradycardia, HF, arrhythmias, gastric pain, flatulence, impotence, bronchospasm, decreased exercise tolerance. Prototype summary: Atenolol Indications: Treatment of angina pectoris,