Ipratropium bromide (atrovent, others) is a quaternary ammonium derivative of atropine. Oxitropium bromide is a quaternary derivative of scopolamine. Ipratropium blocks all subtypes of muscarinic receptors and thus blocks presynaptic muscarinic inhibition of ACh release. The most recently developed and bronchoselective member of this family, tiotropium bromide (spiriva), has a longer duration of action and shows some selectivity for Mj and M3 receptors, with lower affinity for M2 receptors, and thus less presynaptic effect on ACh release.
Ipratropium and tiotropium can produce bronchodilation, tachycardia, and inhibition of secretion similar to that of atropine but with less inhibitory effect on mucociliary clearance relative to atropine. Hence, inhaled ipratropium and tiotropium provide useful anticholinergic therapy of chronic obstructive pulmonary disease and asthma while minimizing the increased accumulation of lower airway secretions encountered with atropine.
Actions of inhaled ipratropium or tiotropium are confined almost exclusively to the mouth and airways. Dry mouth is the only side effect reported frequently. Selectivity results from the very inefficient absorption of the quaternary drug from the lungs or the GI tract. These drugs cause a marked reduction in sensitivity to methacholine in asthmatic subjects, but only modest inhibition of responses to histamine, bradykinin, or PGF2a, and little protection against bronchoconstriction induced by 5-HT or leukotrienes. The therapeutic uses of ipratropium and tiotropium are discussed further in Chapter 27.
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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.