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INTRODUCTION

Drugs with acetylcholine-like effects (cholinomimetics) consist of two major subgroups on the basis of their mode of action (ie, whether they act directly at the acetylcholine receptor or indirectly through inhibition of cholinesterase). Drugs in the direct-acting subgroup are further subdivided on the basis of their spectrum of action (ie, whether they act on muscarinic or nicotinic cholinoceptors).

Acetylcholine may be considered the prototype that acts directly at both muscarinic and nicotinic receptors. Neostigmine is a prototype for the indirect-acting cholinesterase inhibitors.

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DIRECT-ACTING CHOLINOMIMETIC AGONISTS

This class comprises a group of choline esters (acetylcholine, methacholine, carbachol, bethanechol) and a second group of naturally occurring alkaloids (muscarine, pilocarpine, nicotine, lobeline). Newer drugs are occasionally introduced for special applications, for example, the neonicotinoids clothianidin, imidacloprid, and others as insecticides, although some of these insecticides have been banned for outdoor use due to their effect on declining populations of bees and other pollinating insects. The members differ in their spectrum of action (amount of muscarinic versus nicotinic stimulation) and in their pharmacokinetics (Table 7–1). Both factors influence their clinical use.

TABLE 7–1Some cholinomimetics: spectrum of action and pharmacokinetics.

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High-Yield Terms to Learn
Choline ester A cholinomimetic drug consisting of choline (an alcohol) or a choline derivative, esterified with an acidic substance (eg, acetic or carbamic acid); usually poorly lipid soluble
Cholinergic crisis The clinical condition of excessive activation of cholinoceptors; it may include skeletal muscle weakness as well ...

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