McKenna's Pharmacology for Nursing, 2e

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P A R T 5  Drugs acting on the autonomic nervous system

TABLE 30.1

DRUGS IN FOCUS Alpha- and beta-adrenergic agonists

Drug name

Dosage/route

Usual indications

adrenaline (Anapen, EpiPen)

Adult: 0.5–1.0 mg IV for acute treatment; 0.3–0.5 mg SC or IM for respiratory distress; may be used in a nebuliser or as topical nasal drops Paediatric: 0.005–0.01 mg/kg IV, base dose on age, weight and response; do not repeat more than q 6 hours; topical nasal drops for children >6 years as needed 2.5–10 mcg/kg/min IV with dose adjusted based on response Initially 5–10 mcg/kg per minute IV with incremental increases up to 20–50 mcg/kg per minute based on response Adult: 25–50 mg IM, SC or IV for acute treatment; 25–50 mg PO for asthma maintenance Paediatric: 25–100 mg/m 2 IM or SC in four to six divided doses; 3 mg/kg per day in four to six divided doses PO, SC or IV for bronchodilation 15–100 mg in 500 mL NaCl or 5% Dextrose, adjust rate according to blood pressure Paediatric: 0.01 mg/kg IV as a single dose 8–12 mcg base/min IV; base rate and dose on response

Treatment of shock when increased blood pressure and heart contractility are essential; to prolong effects of regional anaesthetic; primary treatment for bronchospasm; as an ophthalmic agent; to produce a local vasoconstriction that prolongs the effects of local anaesthetics

dobutamine (Dobutrex)

Treatment of heart failure

Treatment of shock

dopamine (generic)

ephedrine (generic)

Treatment of hypotensive episodes

metaraminol (generic)

Prevention and management of acute hypotension

noradrenaline (Levophed)

Treatment of shock; used during cardiac arrest to get sympathetic activity

Table 30.1 discusses usual indications for each of these agents. Dopamine, a naturally occurring catecholamine, is the sympathomimetic of choice for the treatment of shock. It stimulates the heart and increases blood pressure but also causes a renal and splanchnic arteri­ ole dilation that increases blood flow to the kidneys. This prevents the diminished renal blood supply and possible renal shutdown that can occur with adren- aline or noradrenaline, which are also naturally occurring catecholamines that interact with both a - and b -adrenergic receptors and are used for the treatment of shock and to stimulate the body after cardiac arrest (see Table 30.1 for additional indications for adrenaline and noradrenaline). Dobutamine, ephedrine and metaraminol are syn- thetic catecholamines. Dobutamine, although it acts at both b -receptor sites, has a preference for b 1 -receptor sites. It is used in the treatment of heart failure because it can increase myocardial contractility without much change in rate and does not increase the oxygen demand of the cardiac muscle, an advantage over all of the other sympathomimetic drugs. Ephedrine stimulates the release of noradren- aline from nerve endings and acts directly on adrenergic receptor sites. Although ephedrine was once used for situations ranging from the treatment of shock

to chronic management of asthma and allergic rhinitis, its use in many areas is declining because of the avail- ability of less toxic drugs with more predictable onset and action. Many OTC cold products contain ephedrine or pseudoephedrine. These products can be used to produce methamphetamine, an often-abused street drug. By law, the sale of these products is now restricted. The products are found behind the counter at pharmacies, not on open shelves; the amount that can be purchased at any given time is limited and in Australia and New Zealand pharmacies maintain a record of multiple pur- chases of pseudoephedrine by any one individual. Metaraminol is very similar to noradrenaline. It is given as a single parenteral injection to manage hypo- tension by increasing myocardial contractility and causing peripheral vasoconstriction. Its use is limited to situations in which dopamine or noradrenaline cannot be used. Pharmacokinetics These drugs are generally absorbed rapidly after injec- tion or passage through mucous membranes. They are metabolised in the liver and excreted in the urine. When used in emergency situations, they are given intra­ venously (IV) to achieve rapid onset of action.