Cholinoceptor-blocking drugs

Question 1

What is the function Muscarinic receptor antagonists (antimuscarinic)

Answer 1

• prevent effects of Ach by blocking its binding to muscarinic cholinergic receptors.

Question 2

ATROPINE

Answer 2

• COMPETITIVE ANTAGONIST
• no distinction among M1, M2, M3 reetpors
• ACTIONS:

–> Decreased secretions (salivary, bronchiolar, sweat)

–> Hyperthermia, Tachycardia, Sedation

–> Mydriasis and cycloplegia

–> urinary retention and constipation

• Does not enter CNS at therapeutic dose (causes mild vagal stim)

Question 3

Uses of Atropine

Answer 3

• USES:

–> Antispasmodic

–> antisecretory

–> management of AChE inhibitor overdose,

–>antidiarrheal,

–> opthalmology

–>prevent vagal reaction

• Treatment for acute intoxications (symptomatic treatment - Physostigmine)

Question 4

IPRATROPIUM (atrovent)

Answer 4

• Nonselective muscarinic antagonist
• MAINLY ACTS ON M3 in bronchial SMC’s and glands when inhaled
• NO CNS ABSORPTION (quaternary amine)
• EFFECTS:

–> Decreases bronchoconstriction

–> Decreases bronchial secretions

• USES: (inhaled)

–> CHRONIC OBSTRUCTIVE LUNG DISEASE

–> Asthma (second line therapy for flares)

Question 5

BENZTROPINE (cogentin)

Answer 5

• Tertiary amine –> CNS absorption
• acts on muscarinic receptors in the brains
• PARASYMPETHETIC EFFECTOR SITES
• ACTION:

–> RE-ESTABLISH DOPAMINERGIC-CHOLINERGIC BALANCE in patients with parkinsons disease (decrease dopaminergic –> cholinergic goes unchecked)

–> Decrease GI/GU secretions and motility

–> INCREASE HEART RATE

Question 6

Hexamethonium and mecamylamine

Answer 6

• GANGLION BLOCKING AGENTS
• ACTION:

–> REDUCE the predominant autonomic tone

–> Prevent baroreceptor reflex changes in the heart

• No longer available clinically due to toxicities

Question 7

What are the effects of Ganglion blocking agents

Answer 7

Question 8

describe Neuromuscular blocking drugs

Answer 8

• Interfere with transmission at the neuromuscular endplate
• TWO TYPES:

–> Non-depolarizing = prevent channel opening

–> Depolarizing = prevent channel closing

• HIGHLY IONIZED and do NOT CROSS CELL MEMBRANES
• USES:

–> primarily as adjuncts during general anesthesia to facilitate tracheal intubation and optimize surgical conditions while ensuring adequate ventilation

Question 9

D-tubocurarine

Answer 9

• NON-DEPOLARIZING NEUROMUSCULAR BLOCKERS
• EFFECTS:

–> Small doses = compete with Ach for binding to receptor

–> high dose = they can enter channel pores

–> BLOCK PRE-JUNCTIONAL Na+ channels –> DECREASE Ach RELEASE

Question 10

Succinylcholine (anetine)

Answer 10

• Depolarizing neuromuscular blockers
• Blockade consists of two phases:
• PHASE 1 –> Binding to Nm –> depolarization

–> persistent depolarization –> paralysis

–> augmented by AChE inhibitors

–> Prevention of channel closing

• PHASE 2 –> end plate finally repolarized, but not depolarized easily again due to DESENSITIZATION

Question 11

describe the Clinical useds of Neuromuscular blockers

Answer 11

• Decrease neuromuscular transmission during anesthesia

–> Larger muscle more resistant to blockade than smaller muscles

–> diaphragm responds last

–> recovery in reverse order

• Tracheal intubation
• control of ventilation
• Treatment of convulsions

–> decrease muscular manifestations of seizures

–> no effects on central processess that occur during convulsions

Question 12

side effects of neuromuscular blockers

Answer 12

• Cardiovascular effects

–> hypotensions (histamine release): prevention with antihistamines

–> High doses –> ganglionic blockade –> severe hypotension

• Hyperkalemia
• increased intraocular pressure
• increased intragastric pressure
• muscle pain