1. Nanoparticulate Systems:
A. Nanoparticles:
These are sub-micron sized carriers that enhance drug penetration by facilitating paracellular or transcellular pathways.
Due to their small size and surface modifications, nanoparticles can improve drug bioavailability by increasing corneal penetration.
B. Liposomes:
These are lipid-based vesicles that can encapsulate both lipophilic and hydrophilic drugs.
Liposomes can merge with cellular membranes, leading to enhanced drug delivery across the barriers.
C. Dendrimers:
These are branching polymers that can carry drug molecules and penetrate barriers.
Their multifunctional surface can be modified for targeted delivery.
2. Mucoadhesive Polymers:
By using polymers that have an affinity for the mucosal surface of the eye, formulations can achieve increased residence time on the ocular surface, thereby allowing more time for drugs to penetrate intraocular barriers.
Examples include chitosan, hyaluronic acid, and polyacrylic acid.
3. Prodrugs:
Prodrugs are derivatives of drug molecules modified to enhance their penetration and stability.
Once inside the body (or specific tissue), they get converted back to the original active drug.
An example in ocular therapeutics is dipivefrin, a prodrug of epinephrine designed for better corneal penetration and reduced systemic side effects.
4. Iontophoresis:
This method involves the application of a small electric current to drive charged drug molecules into the eye.
The technique can significantly increase the delivery of charged drugs across the cornea.
5. Microneedles:
These are minimally invasive systems where tiny needles penetrate the outer layers of the eye to deliver drugs.
For example, microneedles can be used to target the suprachoroidal space for drug delivery, bypassing several barriers.
6. Implants and Devices:
A. Intravitreal Implants:
These are devices placed inside the vitreous humor of the eye to provide sustained drug release, bypassing several barriers to target the retina directly.
B. Punctal Plugs:
Placed in the tear duct, these devices can release drugs slowly over time, increasing ocular residence and reducing drainage.
7. Periocular and Intravitreal Injections:
Direct injection methods bypass the anterior segment barriers of the eye.
Intravitreal injections deliver drugs directly to the retina, while periocular injections target tissues surrounding the outside of the eyeball.
8. Sonophoresis:
Ultrasound waves can be used to temporarily create micropores in the cornea, enhancing drug permeability.
9. Use of Penetration Enhancers:
Agents like surfactants, bile salts, and cyclodextrins can temporarily open tight junctions or enhance drug solubility, thereby increasing drug penetration through barriers.
