Cholinergic Antagonists

CHAPTER 5 (PCOL)

Cholinergic Antagonist

• a general term for agents that bind to cholinoreceptors (muscarinic or nicotinic) and prevent the effects of acetylcholine (ACh) and other cholinergic agonists

Antimuscarinic Agents

• commonly known as anticholinergic drugs, these agents block muscarinic receptors, causing inhibition of muscarinic functions.

Atropine

• a tertiary amine extracted from belladonna alkaloid. It has a high affinity for muscarinic receptors and binds competitively to prevent ACh from binding.

4 hours

General actions of Atropine lasts for ______.

Several Days

Topical administration of Atropine on the eye lasts about _______.

Atropine

Actions:

• blocks muscarinic activity in the eye, resulting in mydriasis (dilation of the pupil), unresponsiveness to light, and cycloplegia.

Atropine

Actions:

• can be used as an antispasmodic to reduce the activity of the GI tract

Atropine and Scopolamine

• are two of the most potent antispasmodic drugs available.

Atropine

Actions:

• at low doses, the predominant effect is a slight decrease in heart rate, results from a blockade of the M1 receptors

Atropine

Actions:

• at higher doses, causes a progressive increase in heart rate by blocking M2 receptors on the sinoatrial node.

Atropine

Actions:

• blocks muscarinic receptors in the salivary glands, producing dryness of mouth (xerostomia)

Atropine

Therapeutic uses:

• exerts both mydriatic and cycloplegia effects, and it permits the measurement of refractive errors without interference by the accommodative capacity of the eyes.

Short-acting antimuscarinics and tropicamide

• have largely replaced atropine due to prolonged mydriasis observed with atropine

Atropine

Therapeutic uses:

• is used as an antispasmodic agent to relax the GI tract

Atropine

Therapeutic Uses:

• is used to treat bradycardia of varying etiologies

Atropine

Therapeutic Uses:

• is sometimes used as an anti-secretory agent to block secretions in the respiratory tract prior to surgery

Atropine

Therapeutic Uses:

• is used for the treatment of organophosphate poisoning, of overdose of clinically used anticholinesterases such as physostigmine, and in some types of mushroom poisoning

Atropine

Pharmacokinetics:

• is readily absorbed, partially metabolized by the liver, and eliminated in urine.

• has a half-life of four hours

Atropine

Adverse effects:

• may cause dry mouth, blurred vision, “sandy eyes”, tachycardia, urinary retention, and constipation

• effects on the CNS includes restlessness, confusion, hallucinations, and delirium

Scopolamine

• another tertiary amine plant alkaloid produces peripheral effects similar to those of atropine

• has greater action on the CNS

Scopolamine

Action:

• one of the most effective drugs available for motion sickness

• also has the unusual effects of blocking short-term memory

Sedation

At lower doses SCOPOLAMINE produces __________.

Excitement

At higher doses, SCOPOLAMINE can produce ________.

Scopolamine

Therapeutic uses:

• is used for the prevention of motion sickness and postoperative nausea and vomiting

Scopolamine

Pharmacokinetics and adverse effects:

• these aspects are similar to those of atropine, with the exception of a longer half-life

Ipratropium and Tiotropium

• are quaternary derivatives of atropine