PHARMACOLOGY Chapter 8

The muscarinic blocking agents act like competitive (surmountable) pharmacologic antagonists; their blocking effects can be overcome by increased concentrations of muscarinic agonists.

Blockers of ganglionic nicotinic receptors act like competitive pharmacologic antagonists, although there is evidence that some also block the pore of the nicotinic channel itself

Tubocurarine is a prototype. It produces a competitive block at the end plate nicotinic receptor, causing flaccid paralysis that lasts 30–60 minutes (longer if large doses have been given)

Although these drugs are nicotinic agonists, not antagonists, they also cause flaccid paralysis. Succinylcholine , the only member of this group used in the United States, produces fasciculations during induction of paralysis

These agents are not receptor antagonists but belong to a class of chemical antagonists. These molecules contain an oxime group, which has an extremely high affinity for the phosphorus atom in organophosphate insecticides. Because the affinity of the oxime group for phosphorus exceeds the affinity of the enzyme-active site for phosphorus, these agents are able to bind the inhibitor and displace the enzyme (if aging has not occurred). The active enzyme is thus regenerated