Direct-acting cholinergic agonists have a direct action on the receptor for acetylcholine. Some drugs are specific for the muscarinic receptor; others are specific for the nicotinic receptor.

The indirect-acting cholinomimetics act by blocking the metabolism of acetylcholine by cholinesterases. These drugs effectively increase the concentration of acetylcholine at all cholinergic synapses.

Activation of nicotinic receptors results in muscle contraction (fasciculations and weakness).

BETHANECHOL is used in the treatment of urinary retention.

The side effects of these drugs are directly related to their interaction with muscarinic receptors.

Nicotine is a direct agonist at nicotinic receptors.

EDROPHONIUM is used in the diagnosis of myasthenia gravis.

NEOSTIGMINE, PYRIDOSTIGMINE, and ambenonium are used in the treatment of myasthenia gravis.

There are no therapeutic uses for the irreversible cholinesterase inhibitors.

PRALIDOXIME and ATROPINE are used to treat poisoning with organophosphates.

The prototypic muscarinic antagonist is ATROPINE.

All of the muscarinic antagonists are competitive antagonists for the binding of acetylcholine to the muscarinic receptor.

Muscarinic antagonists are used preoperatively to reduce secretions.

SCOPOLAMINE is used to prevent motion sickness.

IPRATROPIUM is used in the treatment of chronic obstructive pulmonary disease
(COPD) to produce bronchodilation.

Muscarinic antagonists are used for urinary frequency, urgency, and urge incontinence caused by bladder (detrusor) overactivity.

The competitive neuromuscular blocking drugs are used to produce skeletal muscle relaxation.

SUCCINYLCHOLINE is a depolarizing neuromuscular blocker.

Notice that most of the drug names contain the letters “-cur-”. This should make it easier to recognize the drugs in this group when you see them.

Botulinum toxin blocks the release of acetylcholine at all cholinergic synapses.