pharmacology of glaucoma drugs

Question 1

pharmacology of muscarinic agonist

Answer 1

drug binds to the muscarinic M3 acetylcholine receptors as an agonist in the muscle constrictor. Binding activates the muscle which results in an increase in tension in the ciliary muscle improving drainage and lowering of intraocular pressure.

Question 2

example of muscarinic agonist

Answer 2

pilocarpine

Question 3

what does pilocarpine do

Answer 3

• contracts the ciliary muscles
• constricts pupil
• relaxes lens
• improves drainage

Question 4

ADE of muscarinic agonists

Answer 4

• blurred vision and ocular irritation (burning, itching)
• headache
• also cause miosis which could be permanent in long-term use
  lacrimation is infrequent, retinal detachment is rare

Question 5

pharmacology of beta blockers

Answer 5

• used to be first line treatments but are now adjunctive therapy
• binds as an antagonist to beta-adrenoreceptors present in the ciliary epithelium to stop production of aq humour, although precise mechanism of action is unknown

Question 6

examples of beta-blockers

Answer 6

• timolol

- betaxolol

Question 7

ADE of beta-blockers

Answer 7

• systemic effects: bradycardia, hypotension (fainting), bronchospasm
• may experience stinging sensation and blurred vision

Question 8

what does timolol do

Answer 8

• non selective (can bind to beta 1 and 2 receptors)
• drops IOP by 25%
• fewer local effects
• could have systemic effects

Question 9

what does betaxolol do

Answer 9

• cardioselective
• drops IOP by 20%
• less likely to have systemic ADE

Question 10

pharmacology of adrenergic agonists

Answer 10

• agonists for alpha2-receptors located within ciliary muscles

Question 11

examples of adrenergic agonists

Answer 11

• apraclonidine

- brimonidine (long-term use)

Question 12

what do adrenergic agonists do

Answer 12

• decrease synthesis of aq humour

- increase amount of drains from eye through uveoscleral outflow

Question 13

ADE of adrenergic agonists

Answer 13

• ocular irritation, dry mouth and nose
• taste disturbances
• can decrease sympathetic tone resulting in lowering of BP, fainting, systemic hypotension and dizziness

Question 14

pharmacology of carbonic anhydrase inhibitors

Answer 14

• inhibit carbonic anhydrase 2 (CAMII) enzyme, the major subtype of this enzyme is found in the eye. This prevents HCO3- from forming
• under normal physiological conditions, HCO3- will cross into aq humour, causing sodium to follow. Then, via osmosis, water follows.
• therefore blockage of carbonic anhydrase II will stop this process reducing aq humour formation and thus IOP
  dorzolamide and brinzolamide are both water and lipid-soluble therefore can easily penetrate corneal

Question 15

examples of carbonic anhydrase inhibitors

Answer 15

• azetazolamide
• dorzolamide
• brinzolamide

Question 16

ADE of carbonic anhydrase inhibitors

Answer 16

• acetazolomide cannot tolerate drug - diuresis, loss of appetite, tingling and neutropenia
• topical drugs: ocular irritation, sensation of foreign body in eye = uncomfortable + blurred vision
• corneal staining can occur

Question 17

pharmacology of prostaglandin analogues

Answer 17

• safest and most effective, first line treatment for glaucoma
• binds as an agonist to the prostaglandin F receptor in trabecular meshwork, ciliary muscle and sclera of eye
• these tissues are aq humour outflow pathways. Their extracellular matrix becomes degraded, leading to uveoscleral outflow of aq humour

Question 18

examples of prostaglandin analogues

Answer 18

• latanoprost
• bimatoprost
• travaprost
• tafluprost

Question 19

ADE of prostaglandin analogues

Answer 19

• iris hyperpigmentation (occur gradually and is mostly irreversible)
• eyelash changes (gradually become dark, lengthened and thickened. But reversible upon cessation of treatment)
• conjunctival hyperaemia (redness in sclera of eye)
• eye irritation, blurred vision, allergies and headaches

Question 20

what do prostaglandin analogues do?

Answer 20

• decrease IOP