McKenna's Pharmacology for Nursing, 2e

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C H A P T E R 3 0 Adrenergic agonists

Clinically important drug–drug interactions Increased effects of tricyclic antidepressants and mono- amine oxidase (MAO) inhibitors can occur because of the increased noradrenaline levels or increased receptor stimulation that occurs with both drugs. There is an increased risk of hypertension if a - and b -adrenergic agonists are given with any other drugs that cause hypertension, including herbal therapies and OTC preparations (Box 30.2). Any adrenergic agonist will lose effectiveness if combined with any adrenergic antago- nist. Monitor the person’s drug regimen for appropriate use of the drugs. Prototype summary: Dopamine Indications: Correction of haemodynamic imbalances present in shock. Actions: Acts directly and by the release of noradrenaline from sympathetic nerve terminals; mediates dilation of vessels in the renal and splanchnic beds to maintain renal perfusion while stimulating the sympathetic response. Pharmacokinetics: Route Onset Peak Duration IV 1–2 mins 10 mins Length of infusion T 1/2 : 2 minutes; metabolised in the liver, excreted in the urine. Adverse effects: Tachycardia, ectopic beats, anginal pain, hypotension, dyspnoea, nausea, vomiting, headache.

Safe medication administration

Contraindications and cautions The a - and b -agonists are contraindicated in people with known hypersensitivity to any component of the drug to prevent hypersensitivity reactions ; phaeochromocy- toma because the systemic overload of catecholamines could be fatal ; with tachyarrhythmias or ventricular fibrillation because the increased heart rate and oxygen consumption usually caused by these drugs could exac- erbate these conditions ; with hypovolaemia, for which fluid replacement would be the treatment for the asso- ciated hypotension ; and with halogenated hydrocarbon general anaesthetics (and several industrial solvents), which sensitise the myocardium to catecholamines and could cause serious cardiac effects. Caution should be used with any kind of peripheral vascular disease (e.g. atherosclerosis, Raynaud’s disease, diabetic endarteritis), which could be exacerbated by systemic vasoconstric- tion. Because the sympathomimetic drugs stimulate the SNS, they should be used during pregnancy and breastfeeding only if the benefits to the mother clearly outweigh any potential risks to the fetus or neonate. Adverse effects The adverse effects associated with the use of a - and b -adrenergic agonists may be associated with the drugs’ effects on the sympathetic nervous system: arrhythmias, hypertension, palpitations, angina and dyspnoea related to the effects on the heart and cardiovascular (CV) system; nausea, vomiting and constipation related to the depressant effects on the gastrointestinal (GI) tract; and headache, sweating, feelings of tension or anxiety and piloerection related to the sympathetic stimulation. Because all of these drugs cause vasoconstriction, care must be taken to avoid extravasation of any infused drug. The vasoconstriction in the area of extravasation can lead to cell death in that area. Ephedra, a herb that acts like ephedrine, has been in headlines in recent years because people who were using the herb to promote weight loss died suddenly. The US Food and Drug Administration (FDA) has banned ephedra as a drug and in Australia the TGA imposes a restriction on ephedra which stipulates the ephedrine concentration from all ingredients must not exceed 0.001%. Importation to Australia also requires an import permit-licence. People should be taught about the potential danger of this product. Any person who is at risk for serious reactions to the stimulatory effects of a sympathomimetic—people with narrow-angle glaucoma, dehydration, cerebral or peripheral vascular disease, cardiac disease or arrhythmias, hypertension, renal dysfunction, thyroid disease, diabetes, prostatic disorders, pregnancy or breastfeeding—should receive direct instruction about the dangers of this product.

People being treated with any adrenergic agonists who are also taking ma huang, guarana or caffeine are at increased risk for overstimulation, including increased blood pressure, stroke and death. Counsel people to avoid these combinations. Herbal and alternative therapies BOX 30.2

Care considerations for people receiving α - and β -adrenergic agonists

Assessment: History and examination

■ ■ Assess for contraindications or cautions: any known allergies to these drugs to avoid

hypersensitivity reactions ; phaeochromocytoma, which could lead to fatal reactions due to systemic overload of catecholamines ; tachyarrhythmias or ventricular fibrillation, which could be exacerbated