Pharmacology Flashcards
List 5 routes of administration for eye drugs
- Topical drops/ointment
- Sub-conjunctival injection
- Intra-vitreal injection
- Oral
- Intravenous
Topical drugs must be able to penetrate the cornea. Why can this pose a challenge?
The outer epithelial layer of the cornea is lipophilic so is penetrated by lipid soluble drugs
The inner stroma layer of the cornea is hydrophilic so is penetrated by water soluble drugs
Why is the antibiotic chloramphenicol able to penetrate the cornea easily?
It has both lipophilic and hydrophilic properties
Hydrophilic drugs are limited by the epithelium/stroma
Hydrophobic drugs are limited by the epithelium/stroma
Hydrophilic drugs are limited by the epithelium
Hydrophobic drugs are limited by the stroma
List one factor which can…
- Reduce the hydrophobic nature of the endothelium
- Increase the hydrophobic nature of the endothelium
Ocular surface inflammation can reduce the hydrophobic nature
Lipid layer formed by tears can increase the hydrophobic nature
Topical steroids need both hydrophobic and hydrophilic capabilities to have effect in the eye. This requires chemical modification.
Name a compound which can be added to the steroid to make it more…
-Hydrophobic
-Hydrophilic
Hydrophobic: alcohol or acetate
Hydrophilic: phosphate
When might prednisolone acetate be used? Why?
Acetate = hydrophobic
May be used post-op as it will have good penetration of the uninflamed cornea
When might prednisolone phosphate be used? Why?
Phosphate = hydrophilic
May be used for cornea disease or when only low dose steroid is required because penetration of the cornea is poor
Name a compound which can be added to some drugs to enhance corneal penetration
Benzalkonium
Name a drug which contains Benzalkonium preservative to enhance its corneal penetration
Bimatoprost (used to lower IOP in glaucoma)
Topical drugs which are applied to the cornea are often systemically absorbed by the conjunctiva or nasopharyngeal mucosa instead. How can this be minimised?
By pressing the fingers against the lacrimal lakes to block the nasolacrimal ducts
This punctal occlusion allows the drops to remain in the eye for longer and not be washed into the nasopharynx
Some steroids are administered by subconjunctival injection. What does this mean?
The drug is injected under the conjunctiva covering the sclera or the inner eyelids
Some anaesthetics are administered via subtenon injection. What does this mean?
The drug is injected between the sclera and the Tenon capsule (a layer of connective tissue surrounding the globe)
What is an intravitreal injection? Give 2 examples drugs being administered in this way
Intravitreal injection = injection into the vitreous humor in the posterior segment of the eye
- Anti-VEGF drugs used to treat ‘wet’ macular degeneration can be administered in this way
- Antibiotics in endophthalmitis can be administered this way
Some antibiotics (e.g., in endophthalmitis) are administered by intracameral injection. What does this mean?
The drug is injected into the anterior chamber of the eye (behind the cornea but before the iris)
What is the most common antibiotic used to treat eye infections? Why?
Chloramphenicol
- It is a broad-spectrum antibiotic
- It has hydrophilic and hydrophobic properties so has good corneal penetration