Cholinergic Antagonists

Question 1

Atropine

Answer 1

Alkaloid from Solanaceous family.
Pharmacology: Nonselective competitive antagonist at all muscarinic receptors in CNS and periphery.
Indications: Causes mydriasis (dilation) and cycloplegia (paralysis of ciliary muscle) –> Retinal examination:prevention of synechiae (fused iris with cornea and lense) after surgery or inflamatory response. Used as drops long (5-6 days) action (Toxicity: increased intraocular pressure in closed-angle glaucoma). Mandatory antidote for severe cholinesterase inhibitor poisoning (Cholinergic crisis (dumbells))
Given pre/peroperatively to decrease respiratory secretion and prevent postoperatice pneumonia as well as prevent vagal stimulation. Treat sinus bradycardia or partial heart block (nodal block). Treat myocardial infarction (posterior wall) leading to bradycardia or nodal block.

Question 2

Scopolamine

Answer 2

Pharmacology: Has better CNS penetrability than Atropine.
Indications: Treat motion sickness. Reduces vertigo. Postoperative nausea and vomiting. Combined with morphine to induce anesthesia (facilitates anterograde amnesia).
Adverse Reactions: Tachycardia, blurred vision, xerostomia, delirium. Interactions with other antimuscarinics.

Question 3

Dicyclomine

Answer 3

Pharmacology: Competitive antagonist at M3 receptors. Reduces smooth muscle and secretory activity of gut.
Indications: Irritable bowel syndrome. Minor diarrhea.
Adverse reactions: tachycardia, confusion, urinary retention, increased intraocular pressure. Interactions: with other antimuscarinics.

Question 4

Ipratropium

Answer 4

Pharmacology: Competitive nonselective antagonist at muscarinic receptors (M3).
Indications: Prevention and relief of acute episodes of bronchospasm.
Adverse reactions: Xerostomia, cough. Interactions: with other antimuscarinics.

Question 5

Oxybutynin

Answer 5

Pharmacology: Slightly M3 selective muscarinic antagonists.
Indications: Urge incontinence (induce urinary retention). Postoperative spasms.
Adverse reactions: tachycardia, constipation, increased intraocular pressure, xerostomia. Interactions: with other antimuscarinics.

Question 6

Glycopyrrolate (Robinul)

Answer 6

Pharmacology: Blocks muscarinic receptors on eccrine sweat glands (wide distribution, all across the body, especially in the hands feet, and forehead.
Indications: topical treatment for hyperhidrosis. Botox: blocks acetylcholine release from nerve endings thus sweat gland not stimulated (very costly)

Question 7

Procyclidine hydrochloride (Kemadrin)
Biperiden Hydrochloride (Akineton)
Benztropine (atropine and dyphenhydramine)

Answer 7

Pharmacology: Cholinergic antagonist.
Indications: as an adjunct in the therapy of all forms of parkinsonism –> control of extrapyramidal disorders secondary to neuroleptic drug therapy (e.g., phenothiazines).
Note: Effective only during stage 1 and 2 of parkinson’s disease…to treat tremors.