Anterior segment - ocular surface
Conjunctival Topical Delivery
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Get accessTopical administration into the inferior fornix is the most common route of ocular drug delivery
- Typical drop of ocular medication is 50 microlitres
- The conjunctival sac has a 15-30 microL capacity (dependent on blinking)
- Most applicators deliver 50-100 microL per drop
- A substantial amount is lost due to overspill and tear turnover
- The conjunctival stroma is highly vascular so facilitates effective absorption
- There is also absorption via the nasal and nasopharyngeal mucosa
- Factors affecting absorption:
- Tear film instability affects the time the drug stays in the conj
- Altered tear film pH can affect drug ionization and its diffusion
Precorneal tear film buffers drugs and changes their pH and then their ionization. Purely ionized drugs tend not to penetrate an intact cornea
Depending on the status of the drug, it is delivered in a more acidic or alkaline drop solution to ensure more unionised, therefore more lipid soluble to increase corneal absorption
However: acidic and alkaline preparations can cause irritation and tearing so increase drug clearance
- Environmental temperature and humidity
- Blink rate: increases drug clearance
- Increased viscosity helps increase time in conj
- Polyvinyl alcohol
- Hydroxypropylcellulose
Hot Topic
The corneal epithelium is a greater barrier to hydrophilic than lipophilic drugs