Cholinoceptor-Blocking Drugs

Question 1

Atropine

Answer 1

Muscarinic receptor antagonist (antimuscarinic)

Enters CNS, competes with ACh at M receptors, not selective among M1, M2 or M3

Effects: decreased secretions (salivary, bronchiolar, sweat), mydriasis/cycloplegia, hyperthermia, tachycardia, sedation, urinary retention/ constipation, behavioral excitation/hallucinations
Counteracts peripheral vasodilation caused by choline esters, does NOT affect BP when given alone

Clinical use: antispasmodic, antisecretory, management of AChE inhibitor overdose, antidiarrheal, ophthalmology, prevent vagal reaction in procedures

Tx acute intoxication: symptomatic, physostigmine (antidote0

Question 2

Ipratropium (Atrovent*)

Answer 2

Muscarinic receptor antagonist (antimuscarinic)

Nonselective muscarinic antagonist, mainly acts on M3 bronchial SMCs and glands when inhaled, no CNS absorption

Effects: decreases bronchoconstriction and bronchial secretion

Clinical use (inhaled): COPD (1st line therapy), asthma (2nd line therapy for flares)

Question 3

Benztropine (Cogentin*)

Answer 3

Muscarinic receptor antagonist (antimuscarinic)

CNS absorption, acts on muscarinic receptors in brain, PNS effector sites

Effects: re-establish dopaminergic-cholinergic balance in patients with Parkinson’s disease (PD: decrease dopaminergic–>cholinergic goes unchecked); decrease GI/GU secretions, decrease motility, increase HR

Clinical use: PD=2nd or 3rd line therapy

Question 4

Hexamethonium

Mecamylamine

Answer 4

Nicotinic receptor antagonists (antinicotinic Nn & Nm)

Ganglion blocking agents: reduce predominant autonomic tone, prevent baroreceptor reflex changes in HR, most no longer available clinically b/c of toxicities

vasodilation, hypotension, dilation, decreased venous return, decreased CO, tachycardia, mydriasis, cycloplegia, decreased tone/motility (constipation), urinary retention, xerostomia, anhidrosis

Question 5

Delta-Tubocurarine

Answer 5

Drug acting on Nm receptors- non-depolarizing neuromuscular blockers

Prevent opening of channel when bind to receptor

Clinical use: decrease neuromuscular transmission during anesthesia, tracheal intubation, control ventilation, treatment of convulsions

Side effects: hypotension (histamine release–>prevent with antihistamines), high doses–>ganglionic blockade–>severe hypotension, hyperkalemia, increased intraocular pressure, increased gastric pressure, muscle pain

Question 6

Succinylcholine (Anectine*)

Answer 6

Drugs actin on Nm receptors-Depolarizing neuromuscular blockers

Phase 1: bind and depolarize–>persistent depolarization–>paralysis
Phase 2: endplate repolarized but not depolarized as easily–>desensitization

Clinical use: decrease neuromuscular transmission during anesthesia, tracheal intubation, control ventilation, treatment of convulsions

Side effects: hypotension (histamine release–>prevent with antihistamines), high doses–>ganglionic blockade–>severe hypotension, hyperkalemia, increased intraocular pressure, increased gastric pressure, muscle pain