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Drugs acting on the respiratory system
respiratory disease include aminophylline (generic),
caffeine (
Cafnea
and others) and theophylline (
Nuelin
).
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
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
Mast cell stabilisers block the
release of histamine and SRSA
and inflammation
Inhaled steroids block
inflammation of respiratory
mucosa
Leukotriene receptors
block specific inflammatory
effects
Mucus
Alveolar sacs
Cilia
Anticholinergics block vagus
nerve activity and dilate bronchi
Xanthines relax
smooth muscle
Lung surfactants replace
alveolar surfactant
Sympathomimetics dilate
bronchi and increase rate
and depth of respirations
FIGURE 55.3
Sites of action of drugs
used to treat obstructive pulmonary
disorders.
