McKenna's Pharmacology for Nursing, 2e

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

respiratory disease include aminophylline (generic), caffeine ( Cafnea and others) and theophylline ( Nuelin ).

breathing characterised by apnoeic periods followed by periods of tachypnoea that may reflect delayed blood flow through the brain, and the treatment of apnoea and bradycardia in premature infants. Pharmacokinetics The xanthines are rapidly absorbed from the gastro- intestinal (GI) tract when given orally, reaching peak levels within 2 hours. They are also given IV, reaching peak effects within minutes. They are widely distrib- uted and metabolised in the liver and excreted in urine. Xanthines cross the placenta and enter breast milk (see Contraindications and cautions). Contraindications and cautions Caution should be taken with any person with GI problems, coronary disease, respiratory dysfunction, renal or hepatic disease, alcoholism or hyperthyroid- ism because these conditions can be exacerbated by the

Therapeutic actions and indications The xanthines have a direct effect on the smooth muscles of the respiratory tract, both in the bronchi and in the blood vessels (Figure 55.3). Although the exact mecha- nism of action is not known, one theory suggests that xanthines work by directly affecting the mobilisation of calcium within the cell. They do this by stimulating two prostaglandins, resulting in smooth muscle relax- ation, which increases the vital capacity that has been impaired by bronchospasm or air trapping. Xanthines also inhibit the release of inflammatory mediators and histamine, decreasing the bronchial swelling and narrowing that occurs as a result of these two chemi- cals. See Table 55.1 for usual indications for these drugs. Unlabelled uses include stimulation of respirations in Cheyne–Stokes respiration , an abnormal pattern of

Inhaled steroids block inflammation of respiratory mucosa

Mast cell stabilisers block the release of histamine and SRSA and inflammation

Leukotriene receptors block specific inflammatory effects

Mucus

Cilia

Xanthines relax smooth muscle

Anticholinergics block vagus nerve activity and dilate bronchi

Lung surfactants replace alveolar surfactant

Alveolar sacs

Sympathomimetics dilate bronchi and increase rate and depth of respirations

FIGURE 55.3  Sites of action of drugs used to treat obstructive pulmonary disorders.