Once a drug has been deposited on the lumenal surface of the airway segment, pharmacokinetic processes (viz., absorption, distribution, metabolism or biotransformation, excretion) will govern the amount of drug that reaches its therapeutic site of action. The pharmacokinetic pressures exerted on a drug deposited in the central airways differ from those in the peripheral airways, primarily as a result of the varying constituent cellular populations in each region. For demonstrative purposes, the fates of a bronchodilator drug in the central airways and of a drug destined for systemic absorption in the alveolus are considered in the following sections and are shown in Fig. 1.
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If you suffer with asthma, you will no doubt be familiar with the uncomfortable sensations as your bronchial tubes begin to narrow and your muscles around them start to tighten. A sticky mucus known as phlegm begins to produce and increase within your bronchial tubes and you begin to wheeze, cough and struggle to breathe.