McKenna's Pharmacology for Nursing, 2e

872

P A R T 1 0  Drugs acting on the respiratory system

Clinically important drug–drug interactions Special precautions should be taken to avoid the com- bination of sympathomimetic bronchodilators with the general anaesthetics cyclopropane and halogen- ated hydrocarbons. Because these drugs sensitise the myocardium to catecholamines, serious cardiac compli- cations could occur. The therapeutic effect of indacaterol is blocked with the concomitant use of ß-blockers. Hypokalemic effects of indacaterol may be potenti- ated in individuals using diuretics, steroids or xanthine derivatives. Prototype summary: Adrenaline Indications: Treatment of anaphylactic reactions, acute asthmatic attacks; relief from respiratory distress of COPD and bronchial asthma. Actions: Reacts at α - and β -receptor sites in the sympathetic nervous system to cause bronchodilation, increased heart rate, increased respiratory rate and increased blood pressure. Pharmacokinetics: Route Onset Peak Duration SC 5–10 mins 20 mins 20–30 mins IM 5–10 mins 20 mins 20–30 mins IV Instant 20 mins 20–30 mins Inhalation 3–5 mins 20 mins 1–3 hours T 1/2 : Unknown; metabolised by normal neural pathways. Adverse effects: Fear, anxiety, restlessness, headache, nausea, decreased renal formation, pallor, palpitation, tachycardia, local burning and stinging, rebound congestion with nasal inhalation.

Salbutamol, the prototype drug, is the drug of choice in adults and children for the treatment of acute bronchospasm, including that caused by anaphylaxis; it is also available for inhalation. Because adrenaline is associated with systemic sympathomimetic effects, it is not the drug of choice for people with cardiac condi- tions. See Table 55.1 for usual indications for each of these agents. Pharmacokinetics Sympathomimetics available only as inhalants include eformoterol, indacaterol and salmeterol. Other sympathomimetics are available in various forms. Terbutaline and salbutamol can be used as inhal- ants and as oral and parenteral agents. These drugs are rapidly distributed after injection; they are transformed in the liver to metabolites that are excreted in the urine. The half-life of these drugs is relatively short—less than 1 hour except for indacaterol whose half-life is 49 hours. They are known to cross the placenta and to enter breast milk (see Contraindications and cautions). The inhaled drugs are rapidly absorbed into the lung tissue. Although very little of the drug is absorbed systemically, any absorbed drug will still be metabolised in the liver and excreted in urine. Indaca- terol, however, is eliminated predominantly (~90%) through the fecal route. About 54% of the drug is elim- inated unchanged, and ~23% is excreted as hydoxylated indacaterol metabolite. Contraindications and cautions These drugs are contraindicated or should be used with caution, depending on the severity of the underlying condition, in conditions that would be aggravated by the sympathetic stimulation , including cardiac disease, vascular disease, arrhythmias, diabetes and hyper­ thyroidism. Indacaterol is indicated for people with COPD and not for people with asthma. Indacaterol should not be used for treatment of acute symptoms of COPD or administered more than once a day. Inda- caterol should not be administered with other LABAs. These drugs should be used during pregnancy and breastfeeding only if the benefits to the mother clearly outweigh potential risks to the fetus or neonate. Adverse effects Adverse effects of these drugs, which can be attributed to sympathomimetic stimulation, include CNS stimulation, GI upset, cardiac arrhythmias, hypertension, broncho­ spasm, sweating, pallor and flushing. If the person is taking eformoterol for asthma maintenance, additional doses of drug should not be used for exercise-induced asthma because the cumulative sympathomimetic effects can cause serious cardiovascular problems.

Care considerations for people receiving sympathomimetics

Assessment: History and examination

■ ■ Assess for possible contraindications or cautions : any known allergies to any sympathomimetic or drug vehicle to prevent hypersensitivity reactions ; cigarette use, which affects the metabolism of the drug ; pregnancy or breastfeeding, which require cautious use of the drug ; cardiac disease, vascular disease, arrhythmias, diabetes and hyperthyroidism, which may be exacerbated by sympathomimetic effects ; and use of the general anaesthetics cyclopropane and halogenated hydrocarbons, which sensitise the myocardium to catecholamines and could cause serious cardiac complications if used with these drugs.