McKenna's Pharmacology for Nursing, 2e

465

C H A P T E R 3 0 Adrenergic agonists

b 2 -specific agonists and are used to manage and treat bronchial spasm, asthma and other obstructive pul- monary conditions. These drugs, including salbutamol ( Butamol , Ventolin ), salmeterol ( Serevent ) and terbu- taline, are discussed in Chapter 55, which deals with drugs used to treat obstructive pulmonary diseases. This section specifically addresses isoprenaline ( Isuprel ), which is used as a sympathomimetic for its overall stimulatory properties. Therapeutic actions and indications Therapeutic effects of isoprenaline are related to its stim- ulation of all b -adrenergic receptors. Desired effects of the drug include increased heart rate, conductivity and contractility; bronchodilation; increased blood flow to skeletal muscles and splanchnic beds; and relaxation of the uterus. Its use has decreased over the years as more specific drugs with less toxicity have been developed to treat the cardiac problems isoprenaline was developed to treat. Some research has shown that isoprenaline exerts a “coronary steal” effect, diverting blood away from injured or hypoxic areas of the heart muscle, an effect that can increase the size and extent of an evolving myocardial infarction, further decreasing its usefulness in the clinical setting. There are some emergency situ- ations however, that respond well to isoprenaline. See Table 30.3 for usual indications. Pharmacokinetics Isoprenaline is rapidly distributed after injection; it is metabolised in the liver and excreted in the urine. The half-life is relatively short—less than 1 hour.

Evaluation

■■ a -specific adrenergic agonists, such as phenylephrine and clonidine, stimulate only the a -receptors within the SNS. Clonidine stimulates a 2 -receptors and is used to treat hypertension because its action blocks the release of noradrenaline from nerve axons. ■■ Care must be taken to prevent extravasation when using IV; the vasoconstrictive properties of the drug can cause necrosis and cell death in the area of extravasation. ■■ These drugs should be tapered over 2 to 4 days when discontinued because the adrenergic receptors will be very sensitive and rebound hypertension, tachycardia, arrhythmias and even death can occur. β-SPECIFIC ADRENERGIC AGONISTS Most of the drugs that belong to the class of b -specific adrenergic agonists (Table 30.3), or b -agonists, are ■ ■ Monitor response to the drug (improvement in condition being treated). ■ ■ Monitor for adverse effects (GI upset, CNS and cardiovascular changes). ■ ■ Monitor the effectiveness of comfort measures and compliance with the regimen. ■ ■ Evaluate the effectiveness of the teaching plan (person can name drug, dosage, adverse effects to watch for and specific measures to avoid them). KEY POINTS

TABLE 30.3

DRUGS IN FOCUS Beta-specific adrenergic agonists

Drug name

Dosage/route

Usual indications

Adult: IV injection, 0.02–0.06 mg; IV infusion, 5 mcg/minute; 0.2 mg IM or SC Paediatric: 0.1–1.0 mcg/kg/minute IV has been used

Treatment of shock, cardiac arrest, and certain ventricular arrhythmias; treatment of heart block in transplanted hearts; prevention of bronchospasm during anaesthesia acute bronchospasm and exercise- induced bronchospasm when used by inhalation Treatment and prevention of bronchial asthma and reversible bronchospasm, including exercise-induced bronchospasm (people ≥4 years) Treatment and prevention of bronchial asthma and reversible bronchospasm Treatment and prevention of bronchospasm; treatment of

isoprenaline (Isuprel)

salbutamol (Butamol, Ventolin)

Adult: 2–4 mg t.d.s.–q.i.d. PO, or 1–2 inhalations every 4–6 hours Paediatric: 2 mg t.d.s.–q.i.d. PO, or 1.25–2.5 mg b.d. by inhalation

salmeterol (Serevent)

Adults and children >12 years: 1 inhalation b.d.; 30 minutes before exercise with exercise- induced bronchospasm Adults and children >12 years: 3–4 mg PO up to t.d.s. 0.5 mL SC q 6 hours prn inhalation: 500 mcg–5 mg q 6 hours prn Paediatric: 0.075 mg/kg/dose PO q 4–6 hours prn; Inhalation: 500 mcg q 4–6 hours prn

terbutaline (Bricanyl)