Cholinergic Receptor-Inhibiting Drugs

Question 1

Succinylcholine

Answer 1

• depolarizing NMJ blocker
• produces fasciculations then flaccid paralysis w/i 1 min
• used for tracheal intubation bc effects last only 5-10 mins (via rapid hydrolysis by plasma AChE)

**think: S for Succinylcholine and faSciculations (depolarizing NMJ blocker)

Question 2

atropine

Answer 2

• anti-muscarinic (from belladona plant)
• produces mydriasis (pupil dilation) and cycloplegia (loss of accomodation)

** atropine fever/hyperthermia = blockage of sympa (cholinergic) sweat gland can be lethal in children!

Question 3

antimuscarinic drugs and their toxicity

Answer 3

• benzotropine, scopolamine, atropine, tropicamide, ibatropium, tiotropium, dicyclomine, tolterodine
• Dry as a bone (reduced sweating, lacrimation and salivation); blind as a bat (excessive pupillary dilation); red as a beet (dilation of cutaneous vessels); mad as a hatter (inhibition of muscarinic receptors in CNS)

** non-selective bc they don’t discriminate between M1-M5

Note: at low doses you get slight cardiac slowing due to blockage of inhibitory autoreceptors (M2)

Question 3

Ibatropium and Tiotropium

Answer 3

• anti-muscarinic
• treat asthma/COPD (bronchodilation)

** think: “trop”–> choke –> asthma/COPD

Question 4

Botulinim Toxin A

Answer 4

• degrades SNAP25 and inhibits synaptic vesicle fusion –> no ACh release –> no contraction
• cosmetic purposes
• treats achalasia (abnormal esophageal contractions), strabismus, oromandibular dystonia (spasms of face, jaw)

Question 5

dicyclomine

Answer 5

• anti-muscarinic
• to reduce transient hypermotility of GI tract

*** think: I would die if I couldn’t reduce GI tract hypermotility

Question 6

Tolterodine

Answer 6

• anti-muscarinic
• treat transient cystitis, post-op bladder spasms or incontinence

**think: TTTolterodine = CysTTiTTis and inconTTinence

Question 8

scopolamine

Answer 8

• anti-muscarinic
• treat motion-sickness

* think S (scopolamine= sickness)

Question 9

NMJ blockers

Answer 9

• inhibit Nm receptors
• used as muscle relaxants
• Non-depolarizing blockers act as antagonists that competitively inhibit ACh binding (Tubocurarine)
• depolarizing blockers act as super-agonists that overstimulate the receptor and prevent repolarization (you will see initial transient contraction then relaxation due to desensitization) — Succinylcholine

Question 10

Hexamethonium

Answer 10

• ganglionic blocker (acts on Nn receptor)
• use for Hypertensive crisis (think “H”), bloodless-field surgery
• non-selective bc they inhibit Nn receptors at both sympa and PS ganglia –> broad-range of undesirable effects

Question 11

benzotropine

Answer 11

• anti-muscarinic
• treat Parkinson’s

Question 12

tropicamide

Answer 12

• anti-muscarinic
• produces mydriasis and cycloplegia
• used by eye doctors think: tropicEYEmide
• **very rapidly hydrolyzed

Question 13

Tubocurarine

Answer 13

• blocks Nicotinic (Nm) receptor
• non-depolarizing NMJ blocker
• produces flaccid paralysis (lasts 30-60 mins)
• used for muscle relaxation during surgery w/o deep anesthesia
• AChE inhibitors can reverse the effect (produces more ACh to compete with drug)