Pharmacology Flashcards
What must a topical drug be able to do?
Act on the surface and penetrate the cornea
Describe the structure of the cornea in terms of solubility
Consists of two lipophilic epithelium with hydrophilic stroma in between
Name a drug that is both lipid and water soluble
Chloramphenicol
What is the consequence of ocular inflammation on solubility?
Reduces the hydrophobic nature of the epithelium
How are steroids made more hydrophobic?
Add alcohol or acetate (prednisolone acetate)
How are steroids made more hydrophilic?
Add phosphate (prednisolone phosphate)
Describe predisolone acetate
Hydrophobic, allows good penetration in an uninflammed cornea and is used post-op
Describe prednisolone phosphate
Hydrophilic, has poor penetration in an uninflammed cornea but is used in corneal disease where low doses are required
What chemical can be added to drugs to aid penetration?
Benzalkonium Chloride
Other than aiding penetration what else does benzalkonium chloride do?
It is a preservative emollient that depletes the lipid tear film and kills some microbes
What are the side effects of benzalkonium chloride?
Some patients are allergic and some experience dry eyes
How does systemic absorption of topical drugs occur?
Excess tears go through the nasopharynx and can enter the GI tract
What advice can be given to patients experiencing GI side effects of topical drugs?
Occlude the puncta to limit systemic absorption
Name four other routes of administration (apart from topical)
- subconjunctival (acts like a deposit)
- subtenous (into posterior orbital space)
- intravitreal injection
- intracameral injection
What drugs are often given subconjunctivally?
Steroids and antibiotics
Name four drugs given to patients with ocular inflammation
- Steroids
- NSAIDs
- Anti-histamines
- Mast cell stabilisers
How do steroids work?
Suppress the immune inflammatory response
When are steroids used?
Post op cataracts
Uveitis
Prevent corneal graft rejection
Temporal arterities
What are the signs of uveitis?
Circumcorneal injection - enlargement of ciliary and conjunctival vessels
Keratic precipitates
Yellow/white dots in chorioretinitis with ischaemia
Why are steroids used in temporal arterities?
IV steroids are used as it can cause optic nerve infarction, anterior ischaemic neuropathy and blindness
What are the ocular side effects of steroids?
Cataract
Glaucoma
Exacerbation of virus
What is the only clinically modifiable risk factor for glaucoma?
Raised intraocular pressure
What kind of vision do patients with glaucoma have?
Tunnel vision
What does the treatment of glaucoma aim to do?
Slow the disease down and prevent loss of vision
Name five medications used in glaucoma
- prostanoids
- beta blockers
- carbonic anhydrase inhibitors
- alpha 2 adrenergic agonists
- parasympathomimetics
What is the mechanism of action of prostanoids?
Open the drain
What is the mechanism of action of beta blockers?
Turns off the tap
What is the mechanism of action of carbonic anhydrase inhibitors and how can they be administered?
Turn off the tap can be given orally or IV in an acute situation
How do alpha 2 adrenergic agonists work?
Turn off the tap and open the drain by vasodilation
How do parasympathomimetics work?
Open the drain by pulling on the iris
What drugs are absolutely contraindicated in children?
Alpha 2 agonists due to fatigue and sleep apnoea, they can also cause an allergic reaction
Describe intravitreal administration
Delivers effective concentrations of drug at site but they may be toxic to the retina
When are intravitreal drugs given?
Antibiotics in endophthalmitis
Steroids and anti-VEGF in wet ARMD
What is the mechanism of action of local anaesthetic?
Blocks sodium channels and impedes nerve conduction
When is local anaesthetic used?
Foreign body removal Tonometry Corneal scraping Comfort Cataract surgery
What does tonometry do?
Measure intra-ocular pressure
What is the most common diagnostic dye?
Fluorescein
What are diagnostic dyes used for?
Corneal abrasion, dendritic ulcer, identifying leaks, tonometry, nasolacrimal duct obstruction and angiography
What do some mydriatics do to the ciliary muscles?
Paralyse them
When are parasympathomimetics used?
To decrease pressure
What TB drug can cause ocular side effects?
Ethambutol - optic neuropathy
What ocular side effect can hydroxychloroquine cause?
Bulls Eye Maculopathy
Which heart drug can cause disturbance to colour vision?
Digoxin
When must steroids never be given?
Hepatic Keratitis
