9,10 - Ophthalmic Delivery

Question 1

What are some properties we need to consider for a topical drug formulation? (6 total)

Answer 1

• Physico-chemical drug properties (e.g. Conc. Lipophilicity, MW, charge, pKa)
• Buffer capacity and pH
• Viscosity (to stick to surface)
• Instillation volume (too much means it gets spilled)
• Osmotic pressure, ideally within range, and on lower end of range.
• Preservatives.

Question 2

1) Toxicity depends on… (5 things)
2) Are cations or anion preservatives worse?

Answer 2

1)
- Type
- Conc.
- Dose frequency
- Tear secretion amount
- Severity of disease
2) Cationic which binds to –ve charge of mucus.

Question 3

Describe ointments to treat eye diseases
Pros/cons?

Answer 3

Semisolid drug typically kind of cream to put under eyelids. No water.
Pros:
- High viscosity = stay longer = higher bioavailability
- No sting when applied
- Oily = No dilution from tears, no preservatives, and lubricating
Cons:
- Blurs vision (best to use at night)
- Greasy (discomfort + reflex tearing).

Question 4

Describe emulsions to treat eye diseases
Pros/cons?

Answer 4

Two immiscible liquids like water and oil (+ surfactants)
2) Pros
- Good for oil soluble drugs
- Lubricating
Cons:
- Surfactant is toxic
- Low stability eventually leads to cracking
- Costly

Question 5

2 approaches to increasing bioavailability?

Answer 5

Increase corneal penetration
Prolong contact time

Question 6

Describe MPPs

Answer 6

Can freely move pass tear soluble mucins and stay at membrane-bound mucins to prevent being washed off.
This prolongs contact time

Question 7

Describe how prostaglandin analogues e.g. Latanoprost improve on corneal permeability?

Answer 7

Ester prodrugs are more lipophilic and can penetrate corneal epithelium. Activated by esterases in stroma which makes them into the actual drugs which are more hydrophilic thus penetrates stroma easily.

Question 8

Describe importance of surface tension in eyedrops.

Answer 8

E.g. Eyesol has low surface tension so less drugs per drop and it spreads easily across corneal surface without getting wiped off.

Question 9

How do lubricants work?
How do liposomal sprays work?

Answer 9

Replenish lipid layer of tear film. Homogenous (1 phase)

Heterogenous (2 phase) sprays onto lids to replenish lipid layer

Question 10

How do microemulsions work?

Answer 10

First off they look clear because tyndall effect doesn’t occur because drug particles really small. Very liquidy but when adding more water, they turn to crystallin viscous thingy.
example given: At physiological pH, polymers interlink causing lipid emulsions to get released to restore lipid layer of tear film.

Question 11

Intracemeral implants work how?

Answer 11

Inject implant under sclera. Implant + H2O -> drug release from polymer scaffhold. Polymer scaffhold biodegrades when no drugs left. Used as anti-glaucoma.

Question 12

How can CLs be used to deliver drugs?

Answer 12

Presoak them with drug solution.
- Requires dipping every morning (must be careful of contaminating solution with hands)

Question 13

Describe Iontophoresis

Answer 13

Stick device onto eye for 5 min. Electode causes H2O to become OH- and repel from device to eye. This causes drug to also repel (like repels like) towards the eye. Enters anterior and posterior segment of eye.

Question 14

Describe intravitreal injections
Pros/cons?

Answer 14

Pros:
- Injection close to retina
- Rapid onset
- Small dose needed
Cons:
- Invasive
- Limited volume (or else increase IOP)
- Short drug half life
(Increase frequency of injections and higher cost reduces compliance).