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  • Image not available.Ester linkage is essential for effective binding of the anticholinergics to the acetylcholine receptors. This competitively blocks binding by acetylcholine and prevents receptor activation. The cellular effects of acetylcholine, which are mediated through second messengers such as cyclic guanosine monophosphate (cGMP), are inhibited.
  • Image not available.Anticholinergics relax the bronchial smooth musculature, which reduces airway resistance and increases anatomic dead space.
  • Image not available.Atropine has particularly potent effects on the heart and bronchial smooth muscle and is the most efficacious anticholinergic for treating bradyarrhythmias.
  • Image not available.Ipratropium solution (0.5 mg in 2.5 mL) appears particularly effective in the treatment of acute chronic obstructive pulmonary disease when combined with a β-agonist drug (eg, albuterol).
  • Image not available.Scopolamine is a more potent antisialagogue than atropine and causes greater central nervous system effects.
  • Image not available.Because of a quaternary structure, glycopyrrolate cannot cross the blood–brain barrier and is almost always devoid of central nervous system and ophthalmic activity.

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One group of cholinergic antagonists has already been discussed: the nondepolarizing neuromuscular-blocking agents (see Chapter 9). These drugs act primarily at the nicotinic receptors in skeletal muscle. This chapter presents the pharmacology of drugs that block muscarinic receptors. Although the classification anticholinergic usually refers to this latter group, a more precise term would be antimuscarinic.

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In this chapter, the mechanism of action and clinical pharmacology are introduced for three common anticholinergics: atropine, scopolamine, and glycopyrrolate. The clinical uses of these drugs in anesthesia relate to their effect on the cardiovascular, respiratory, cerebral, gastrointestinal, and other organ systems (Table 11–1).

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Table Graphic Jump Location
Table 11–1. Pharmacological Characteristics of Anticholinergic Drugs.1
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Image not available.Anticholinergics are esters of an aromatic acid combined with an organic base (Figure 11–1). The ester linkage is essential for effective binding of the anticholinergics to the acetylcholine receptors. This competitively blocks binding by acetylcholine and prevents receptor activation. The cellular effects of acetylcholine, which are mediated through second messengers such as cyclic guanosine monophosphate (cGMP), are inhibited. The tissue receptors vary in their sensitivity to blockade. In fact, muscarinic receptors are not homogeneous, and receptor subgroups have been identified: neuronal (M1), cardiac (M2), and glandular (M3) receptors.

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Figure 11–1.
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Physical structures of anticholinergic drugs.

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General Pharmacological Characteristics

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In clinical doses, only muscarinic receptors are blocked by the anticholinergic drugs discussed in this chapter. The extent of the anticholinergic effect depends on the degree of baseline vagal tone. Several organ systems are affected.

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Cardiovascular

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Blockade ...

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