Respiratory system: chronic obstructive pulmonary disease

22 Respiratory system


chronic obstructive pulmonary disease





Questions



image What is chronic obstructive pulmonary disease?

image What drugs are used for its treatment?

Chronic obstructive pulmonary disease (COPD) is characterized by airflow obstruction that is partly reversible and progressively deteriorates. Those who suffer from COPD have reduced lung function (as expressed by forced expiratory volume in one second; FEV1) and exacerbation of symptoms (including cough and mucus secretion). Because of the nature of this disease, subjects can suffer from a diminished capacity to undertake physical exertion and have a poor quality of life. Cigarette smoking and exposure to indoor pollution (e.g. smoke from burning of biomass fuels) are major factors in its morbidity (Fig. 3.22.1). Smoking cessation should be encouraged because it is the only form of ‘treatment’ that has been shown to reduce disease progression. However, this can be difficult for a majority of smokers because of nicotine addiction. It is, therefore, of interest that the antidepressant bupropion given for a short period improves the likelihood of smoking abstinence.


image

Fig. 3.22.1 Chronic obstructive pulmonary disease.(A) Pathophysiology; (B) a bronchiole in bronchitis;(C) emphysema.



Drug treatment


A number of pharmacological agents are used in the management of COPD but none halts the accelerated decline in the lung function seen in this disease.



Bronchodilators


Bronchodilator drugs can improve airflow obstruction but the poorly reversible nature of the obstruction in this disease means that only variable increases in baseline FEV1 will be demonstrated. However, the benefit to the patient comes in the form of an increase in ventilation at a lower functional residual capacity and reducing hyperinflation, which improves the capacity to exercise.



Anticholinergic drugs


Anticholinergic drugs including ipratropium bromide, oxitropium bromide and tiotropium bromide antagonize the actions of acetylcholine release from parasympathetic nerves innervating the lung. As a consequence airway smooth muscle relaxation and inhibition of mucus secretion are desirable beneficial actions. Muscarinic M2 receptors are found on the terminal ending of parasympathetic nerves and activation of these receptors leads to a reduction in the release of acetylcholine from parasympathetic nerves. In contrast, activation of M3 receptors on effector cells like airway smooth muscle leads to contraction. It would be desirable to antagonize the actions of acetylcholine selectively at M3 but not M2 receptors, as the latter act as a negative feedback mechanism to limit the release of acetylcholine from parasympathetic terminals. Ipratropium bromide is a non-selective antagonist but nonetheless is effective in the treatment of COPD. However, its short duration of action necessitates self-medication on a regular basis. In contrast, tiotropium bromide has affinity for both receptor subtypes but appears to dissociate rapidly from M2 receptors while remaining firmly bound to the M3 receptor and, as a consequence, has a prolonged duration of action (once daily treatment). Tiotropium bromide significantly improves lung function, reduces symptoms, increases quality of life and reduces exacerbation rates.

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Jul 18, 2016 | Posted by in PHARMACY | Comments Off on Respiratory system: chronic obstructive pulmonary disease

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