Pharm: Cholinergics

Question 1

Hexamethonium, mecamylamine, trimethaphan

Answer 1

Mechanism: competitively inhibit N receptors on autonomic ganglia > block autonomic outflow to sympathetic and parasympathetic NS
Use: hypertensive emergencies
SE: sedation, cycloplegia, hypotension, tachycardia, constipation, urinary retention

Question 2

Pilocarpine, carbachol

Answer 2

Mechanism: muscarinic (M1,2,3) agonist applied to the eye, causes contraction of sphincter muscle > opens canal of Schlemm and contraction of ciliary muscle > opens trabecular mesh-work; carbachol is also a N agonist
Use: narrow and wide angle glaucoma
SE: minimal when applied topically to eye

Question 3

Methacholine

Answer 3

Mechanism: muscarinic (M1,2,3) agonist; inhaled it causes bronchoconstriction
Use: bronchial challenge for dx of reactive airway disease
SE: contraindicated in severe asthma and COPD, can cause hypotension and bradycardia

Question 4

Bethanechol

Answer 4

Mechanism: M2,3 agonist; causes bladder wall contraction and sphincter relaxation > urination; also increases gut motility
Use: neurogenic ileus and urinary retention postpartum or post-op
SE: bradycardia, hypotension, sweating, salivation, diarrhea (does not cross BBB)

Question 5

Atropine

Answer 5

Mechanism: M1,2,3 antagonist; blockade of M1 > sedation, psychosis; blockade of M2 > tachycardia; blockade of M3 > decreased GI motility, urinary retention, cycloplegia
Use: antidote to cholinesterase poisoning (insecticide), treats bradycardia in emergency, urinary incontinence, induces mydriasis
SE: hyperthermia, flushing, dry mouth, cycloplegia, psychosis, tachycardia

Question 6

Benztropine

Answer 6

Mechanism: M1,2,3 antagonist; inhibits M1 receptors in the striatum > block stimulation of GABA-ergic activity
Use: treats tremor and rigidity in Parkinson’s
SE: dry mouth, irritability and confusion, constipation, urinary retention, hyperthermia, sedation, mydriasis (contraindicated in pts with narrow angle glaucoma)

Question 7

Ipratropium

Answer 7

Mechanism: M3 antagonist; inhaled, it causes bronchodilation
Use: COPD, asthma
SE: minimal

Question 8

Oxybutynin, propantheline

Answer 8

Mechanism: M1,2,3 antagonist; decreases bladder wall constraction and increases sphincter tone > urinary retention; also reduces sweating
Use: urinary incontinence, hyperhidrosis
SE: sedation, dry mouth, blurred vision, psychosis, tachycardia

Question 9

Neostigmine, physostigmine, pyridostigmine, edrophonium

Answer 9

Mechanism: reversibly inhibits acetylcholinesterase > elevates amount of ACh in synapse; physostigmine can cross the BBB, neostigmine cannot
Use: treatment of MG (neostigmine and pyridostigmine), diagnosis of MG (edrophonium), reversal of atropine poisoning, glaucoma (physostigmine)
SE: diarrhea, bronchoconstriction, salivation, flushing, nausea, bradycardia

Question 10

Donepezil, galantamine, rivastigmine, tacrine

Answer 10

Mechanism: reversibly inhibit AChE > elevate amount of ACh in synapse
Use: Alzheimer’s disease (slows progression)
SE: nausea, hepatotoxicity

Question 11

Echothiophate, isoflurophate

Answer 11

Mechanism: inhibit AChE > increased ACh in synpase; cause contraction of ciliary muscle
Use: wide-angle glaucoma (applied topically)
SE: none when applied topically; malathion and parathion are poisons (nerve gas) with similar mechanism

Question 12

Pralidoxime

Answer 12

Mechanism: reverses cholinesterase inhibitor binding > permits breakdown of ACh by AChE
Use: organophosphate poisoning, overdose of -stigmine drugs
SE: flushing, tachycardia, dry mouth, blurry vision, sedation