Ocular Pharmacology Flashcards
What is required of topical preparations?
Required to act on a surface = need corneal penetration
What drug class are good for corneal penetration?
Low molecular weight drugs
How is the cornea structured?
Lipid : water : lipid sandwich = epithelium is lipophilic/hydrophilic, stroma is lipophobic/hydrophilic
How does the structure of the cornea affect where drugs can be absorbed?
Lipid soluble drugs penetrate the epithelium, water soluble drugs penetrate the stroma
What is an example of a drug that crosses the cornea easily?
Chloramphenicol = has both lipophilic and hydrophilic properties
What effect may the tear film have on drug penetration?
May impeded drug penetration (lipid layer)
How does the structure of the cornea impact what drugs have limited absorption?
Hydrophilic drugs are limited by the epithelium, hydrophobic drugs are limited by the stroma
What properties do topical steroids need to have?
Need to be both hydrophobic and hydrophilic = chemical modification may be needed
What are some ways that steroids can be modified?
Alcohol or acetate may be added to make steroid more hydrophobic, phosphate may be added to make steroid more hydrophilic
What are some features of prednisolone acetate?
Hydrophobic, good penetration in uninflamed cornea, used post-operatively
What are some features of prednisolone phosphate?
Hydrophilic , poor penetration in uninflamed cornea, used for corneal disease or when low dose steroids are needed
What are the common uses of benzalkonium chloride?
Surfactant and antibacterial agent = commonly found in household cleaning products
How may corneal penetration be enhanced?
By adding benzalkonium as a preservative = disrupts lipid layer of tear film and aids penetration of some drugs
What are some features of bimatoprost 0.03%?
Drug used to lower intra-ocular pressure in glaucoma, has benzalkonium concentration of 0.05 mg/ml
What is the benzalkonium concentration in bimatoprost 0.01%?
0.2 mg/ml
What are some features of the systemic absorption of drugs?
Tears are pumped out of the lacrimal sac rapidly, excess gains systemic absorption at nasopharynx, limited by punctal occlusion
What are some routes of administration?
Subconjunctival, subtenons
What are the types of intra-ocular injection?
Intravitreal, intracameral
What are some uses of ophthalmic drugs?
Treatment of infection, treatment of inflammation, treatment of glaucoma, diagnostic eye drops, intra-ocular injections, ocular toxicity
What are some common anti-inflammatory agents used?
Steroids, topical NSAIDs, antihistamines, mast cell stabilisers
What are the actions of steroids?
Suppress inflammation, allergy and immune response
What are steroids commonly used topically for in the eye?
Post-operative cataracts, uveitis and to prevent corneal graft rejection
What are the local effects of steroids?
Cataracts, glaucoma, exacerbation of viral infection
What are some systemic effects of steroids?
Gastric ulceration, immunosuppression, osteoporosis, weight gain, diabetes
What are some different strengths of steroids?
FML, predsol (prednisolone phosphate), betamethasone, dexamethasone/prednisolone acetate
What are antihistamines and mast cell stabilisers used for?
Hayfever and allergic conjunctivitis
What are NSAIDs mainly used for?
Pain relief (i.e post-refractive laser)
What is glaucoma?
Group of diseases characterised by a progressive optic neuropathy resulting in field defects
What is the only modifiable risk factor for glaucoma?
Raised intra-ocular pressure
What are some features of glaucoma?
Usually asymptomatic, screened for by optometrist, chronic disease, usually slowly progressive, incidence increases with age
What are some treatments for glaucoma?
Prostanoids = latanoprost
Beta blockers = timolol, betaxolol, levobunolol cartelol
Carbonic anhydrase inhibitors = topical (dorzolamide) or systemic (acetazolamide)
Alpha 2 adrenergic antagonists = brimonidine (contraindicated in children as it causes sleep apnoea)
Parasympathomimetic = pilocarpine
Cosopt = combo of dorzolamide and timolol
What is the benefit of intravitreal delivery?
Delivers effective concentration of drug at the target site instantly
What is an issue with intravitreal delivery?
Many drugs are toxic to the retina
What is intravitreal delivery used for?
Delivery of antibiotics in endophthalmitis and intra-ocular steroids
How does local anaesthetic work?
Blocks sodium channels and impedes nerve conduction
What is local anaesthetic used for?
FB removal, tonometry (intra-ocular pressure measurement), corneal scraping, comfort, cataract surgery
What is the most common diagnostic dye?
Fluorescein
What is fluorescein used for?
Showing corneal abrasion and dendritic ulcers
Identifying leaks and nasolacrimal duct obstruction
Tonometry and angiography
What are some examples of mydriatics?
Tropicamide, cyclopentolate
What do mydriatics do?
Cause pupil dilation by blocking parasympathetic supply to iris = cause cycloplegia (stop lens from focusing)
What are some side effects of mydriatics?
Blurring of vision, acute angle closure glaucoma
What type of drug should never be used to treat herpetic keratitis?
Steroids
What do sympathomimetics do?
Act on sympathetic system to cause pupil dilation
What can some sympathomimetics cause?
Cycloplegia = some can (atropine) and some cannot (phenylephrine)
