Chapter 8: Cholinoceptor Blockers & Cholinesterase Regenerators

Question 1

2 subclasses of cholinoceptor antagonists based on their spectrum of action:

Answer 1

Antimuscarinic

1. M1-selective (pirenzepine)
2. (Slightly) M3-selective (darifenacin)
3. Nonselective (atropine)

Antinicotinic

1. Ganglion blockers (hexamethonium)
2. Neuromuscular blockers (tubocurarine)

Question 2

_____

• The prototypical nonselective muscarinic blocker
• Found in Atropa belladonna
• Relatively lipid-soluble and readily crosses membrane barriers
• Eliminated partially by metabolism in the liver and partially unchanged in the urine
• Half-life is approximately 2 hours
• Duration of action of normal doses is 4–8 h EXCEPT in the eye

Answer 2

Atropine

Question 3

Hyperthermia induced by antimuscarinic drugs; caused mainly by inhibition of sweating

Answer 3

Atropine fever

Question 4

Marked cutaneous vasodilation of the arms and upper torso and head by toxic doses of antimuscarinic drugs, especially atropine; mechanism unknown

Answer 4

Atropine flush

Question 5

Paralysis of accommodation; inability to focus on close objects

Answer 5

Cycloplegia

Question 6

What do you call a drug that constricts the pupil?

Answer 6

Miotic

Question 7

What do you call a drug that dilates the pupil?

Answer 7

Mydriatic

Question 8

Effects of muscarinic blocking drugs on glands

Answer 8

1. Marked reduction of salivation
2. Moderate reduction of lacrimation, sweating
3. Less reduction of gastric secretion

Question 9

A muscarinic blocker used as standard therapy for motion sickness, available as a transdermal patch formulation

Answer 9

Scopolamine (hyoscine)

Question 10

Antimuscarinic drugs are used to cause mydriasis, as indicated by the origin of the name belladonna (“beautiful lady”).
What is the duration of action of these drugs?

Answer 10

Atropine (>72 h)
Homatropine (24 h)
Cyclopentolate (2–12 h)
Tropicamide (0.5–4 h)

Question 11

A quaternary antimuscarinic agent used by inhalation to promote bronchodilation in asthma and chronic obstructive pulmonary disease (COPD)

Answer 11

Ipratropium

Question 12

_____ is an analog of ipratropium with a longer duration of action

Answer 12

Tiotropium

Question 13

Atropine toxicity

Answer 13

“Dry as a bone” - sweating, salivation, and lacrimation are all significantly reduced or stopped

“Hot as a pistol” - blockade of thermoregulatory sweating may result in hyperthermia or atropine fever

“Red as a beet” - dilation of the cutaneous vessels of the arms, head, neck, and trunk also occurs at these doses; the resulting “atropine flush”

“Mad as a hatter” - CNS toxicity includes sedation, amnesia, and delirium or hallucinations

“Blind as a bat” - cycloplegia

Question 14

Relative contraindications of the antimuscarinic agents

Answer 14

1. Infants because of the danger of hyperthermia
2. Glaucoma (especially the closed-angle form)
3. Men with prostatic hyperplasia

Question 15

A partial nicotinic receptor agonist given by mouth, shown to have some benefit in smoking cessation.

Answer 15

Varenicline

Question 16

The prototype cholinesterase regenerator, containing an oxime group, which has an extremely high affinity for the phosphorus atom in organophosphate insecticides

Answer 16

Pralidoxime

Question 17

Antimuscarinic agents used in parkinsonism

Answer 17

1. Benztropine
2. Biperiden
3. Trihexyphenidyl

Question 18

Why is ipratropium the preferred bronchodilator in patients with comorbid COPD and heart disease?

Answer 18

Less likely to cause tachycardia and cardiac arrhythmias