Cholinoceptor Antagonists

Question 1

Nicotinic receptor antagonists: any name for them? Describe the two parts of their mechanism and comment on their efficacy and affinity. Describe their effects.

Answer 1

Ganglion blocking drugs. Bind to receptors and/or block the ion channel. Blocking the ion channel is use-dependent, incomplete and requires no affinity. Their effect depends on the dominant system at the time of administration e.g. administer at rest= hypotension, dilation of pupil, constipation, less exocrine secretion.

Question 2

Hexamethonium- what is? Dominant mechanism? Use?

Answer 2

Nicotinic recepctor agonist (reversible). Mainly an ion channel blocker. Was 1st anti-hypertensive but lots of side effects.

Question 3

Trimetaphan- what is it? Dominant mechanism? What is it used for? Administration?

Answer 3

Nicotinic receptor agonist (reversible). Mainly a receptor binder.Used to cause hypotension during surgery. IV adminsitration.

Question 4

Name the poison of the common krait and what type of drug it is.

Answer 4

a-bungarotoxin. IRREVERSIBLE nicotinic receptor antagonist.

Question 5

Atropine- what is it? Describe its effect on the CNS.

Answer 5

Muscarinic receptor antagonist. Normal dose- little effect. Toxic dose- mild restlessness–> agitation.

Question 6

Hyoscine- what is it? Describe its effect on the CNS.Name 2 uses.

Answer 6

Muscarinic receptor antagonist. Normal dose- sedation, amnesia. Toxic dose- CNS depression/ paradoxical excitation. Slightly M1 selective. Used as a anaesthetic premedication (Heart, M2, airways, M3, salivary glands, M1 and M3) and as a motion sickness patch.

Question 7

Tropicamide- what is it? Mechanism? What is it used for?

Answer 7

Muscarinic receptor antagonist (M3). Blocking of M3 receptors on circular muscle of the iris causes dilatation. Used for examination of the retina.

Question 8

Name 3 other uses of muscarinic receptor antagonists.

Answer 8

Irritabel bowel syndrome medication, astham medication (ipatropium bromide), Parkinson’s.

Question 9

Name 4 side effects of muscarinic receptor antagonists.

Answer 9

Hot as hell, dry as a bone, mad as a hatter and blind as a bat.

Question 10

What could you use to treat atropine poisoning?

Answer 10

Physostigmine.

Question 11

Name a parasympatholytic and its mechanism.

Answer 11

Botulinim toxin- creates a SNARE complex that prevents Ach vesicles from docking with the presynaptic membrane, preventing exocytosis into the synapse.

Question 12

What is glaucoma? Name 3 options to treat it.

Answer 12

Glaucoma: when the intraocular pressure (normally around 15mmHg) increases such there is damage to nerve fibres at the optic nerve head- resulting in progressive optic atrophy.

Pilocarpine: cholinergic agonist. Stimulates circular muscle of the iris to cause constriction of the pupil. This opens more channels in the trabecular meshwork fro drainage via the canal of Schlemm.

Sympathomimetic drugs can also be used, e.g. dipvefrine, which stimulate a1 receptors on the vessels of the ciliary bodies, decreasing aqueous humour production (despite also multilingual B1 and dilation)

Beta blockers- block B1 receptor on ciliary body, reducing aqueous humour production.