Ocular Drug Delivery, barriers, overcoming barriers, recent advances, routes of administration, structure of eye, formulation development, evaluation

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OCULAR DRUG
DELIVERY
SYSTEM
UNNATI GARG
M. Pharm (Pharmaceutics)
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INTRODUCTION
• A drug delivery system to target a particular tissue of the
eye.
• The eye can be broadly classified into two segments:
anterior and posterior.
• Different anatomical and physiological barriers present.
• Route of administration can be: topical, systemic,
periocular or intravitreal
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Figure 1. Diagram of the human eye. The anterior segment of the eye contains the cornea,
iris, ciliary body, and lens. The posterior segment of the eye consists of the vitreous
humor, retina, choroid, and optic nerve

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BARRIERS
• Ocular barriers of anterior and posterior segments retard
the passive absorption of various therapeutic agents.
• Two types: Static and Dynamic Barriers
• Static Barriers: Corneal epithelium, Corneal stroma,
corneal endothelium, sclera, blood aqueous barrier.
• Dynamic barriers: Tear drainage, retinal-blood barriers,
choroidal blood and lymphatic circulation.
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• Lipophilic corneal epithelia allows absorption of hydrophobic
drugs but acts as a barrier for paracellular diffusion of
hydrophilic drugs. (Prevents absorption of more than 10 Å
molecules)
• Sclera provides higher trans scleral permeability than the
cornea for hydrophilic compounds diffusing through the
collagen network.
• The choroid is a vascular natured dynamic barrier, which
impedes drug delivery by trans-scleral pathway
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BARRIERS

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• Retina is a significant limiting factor for diffusion of molecules
with larger radius and molecular weight greater than 76 kDa.
• The inner limiting membrane (ILM) of retina severely confines
passaging of macromolecules over 150 kDa molecular weight.
• The blood retinal barrier (BRB): outer blood retinal barrier
(oBRB) and an inner blood retinal barrier (iBRB)
• Barriers between the blood and the retina having tight junction
proteins between the cells
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BARRIERS

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• Bruch’s membrane
• Blood aqueous barrier consists of an epithelial and an
endothelial barrier.
• The permeability of drugs through the blood aqueous
barrier is determined by osmotic pressure and physical-
chemical characteristics of drug molecules.
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BARRIERS

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ROUTES OF
ADMINISTRATION
Topical Administration:
• Solutions, suspensions, emulsions and ointments
• Diseases like allergic conjunctivitis and glaucoma are
treated.
• Factors like solution drainage, blinking, tear film, tear
turnover affect the bioavailability (<5%)
• High patient compliance, non-invasive and self
administrable.
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Systemic (Parenteral) Administration:
• the blood–aqueous barrier and blood–retinal barrier are
the major barriers.
• Diseases like scleritis, episcleritis and retinitis can be
treated.
• High dosing causes toxicity.
• Bioavailability < 2%
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ROUTES OF
ADMINISTRATION

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Periocular Administration:
• The periocular route includes subconjunctival, subretinal,
retrobulbar, and peribulbar administration.
• periocular injections can reach the posterior segment by
different pathways: transscleral pathway; systemic
circulation through the choroid
• and the anterior pathway through the tear film, cornea,
aqueous humor, and the vitreous humor
• Suitable for depot formulations; fewer complications;
anaesthesia administration; treatment of Diabetic macular
edema 11
ROUTES OF
ADMINISTRATION

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Figure: Routes of drug administration to the eye

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Intravitreal Administration:
• In intravitreal administration, small molecules can rapidly
distribute through the vitreous, whereas the diffusion of
larger molecules is restricted.
• Sustains drug levels; evades BRB.
• Can cause retinal detachment; haemorrhage; cataract
• Treating Age-related macular degeneration, DME,
Posterior uveitis
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ROUTES OF
ADMINISTRATION

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FORMULATIONS
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Ophthalmic Solutions (E.g. Atropine Sulphate eye drops)
Suspensions (E.g. Tobramycin)
Emulsions (E.g. Cyclosporine-A)
Ointments (E.g. Chloramphenical)
Intravitreal injections (E.g. Clindamycin)
i.v injections (E.g. Amphotericin-B)
Ocular Inserts (E.g. Pilocarpine)

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OVERCOMING
BARRIERS
• Using Penetration enhancers
• Adjusting viscosity
• Use of Prodrugs
• Using novel drug delivery systems
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EVALUATION
Sterility Test
Clarity Examination
Osmolality and pH
Particle Size and Morphology
Mucoadhesion Test
Stability Study
Toxicity and Biocompatibility
Studies
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Advantages
• Accurate and uniform
dosing
• Sustained and controlled
release can be achieved
• Self administration can be
possible
• Lower side effects
• Faster absorption of drug
Disadvantages
• Poor bioavailability
• Termination of dosage not
possible
• Interference with vision
• Loss of drug possible if
eye is rubbed

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RECENT ADVANCES
Recent Advances
Micro- and
nanoparticle
s
Implants
Liposomes
and
Niosomes
Hydrogels
Dendrimer
Port Delivery
Systems
Drug-eluting
Contact
lenses
Microneedle
Iontophoresi
s
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CONCLUSION
Due to the ocular barriers, optimal drug delivery to the eye
still remains a big challenge. modern technology seems to
be logically explored in various ways over the conventional
approaches, examples of non-conventional approaches
being the use of nanotechnology, microspheres, liposomes,
appropriate prodrug in situ forming gel and iontophoresis
as effective means of ocular drug delivery enhancing ocular
absorption along with reduction in side effects.
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REFERNCES
1. Gote V, Sikder S, Sicotte J, Pal D. Ocular Drug Delivery: Present
Innovations and Future Challenges. J Pharmacol Exp Ther. 2019 Sep;
370(3):602-624. doi: 10.1124/jpet.119.256933.
2. Kang-Mieler, J.J., Rudeen, K.M., Liu, W. et al. Advances in ocular drug
delivery systems. Eye; 2020; 34, 1371–1379. doi: 10.1038/s41433-020-
0809-0.
3. Kim HM, Woo SJ. Ocular Drug Delivery to the Retina: Current Innovations
and Future Perspectives. Pharmaceutics. 2021 Jan 15;13(1):108. doi:
10.3390/pharmaceutics13010108.
4. Mazet R, Yaméogo JBG, Wouessidjewe D, Choisnard L, Gèze A. Recent
Advances in the Design of Topical Ophthalmic Delivery Systems in the
Treatment of Ocular Surface Inflammation and Their Biopharmaceutical
Evaluation. Pharmaceutics. 2020 Jun 19;12(6):570. doi:
10.3390/pharmaceutics12060570.
5. Gaudana, R., Ananthula, H.K., Parenky, A. et al. Ocular Drug
Delivery. AAPS J. 2010; 12(3); 348–360. doi:10.1208/s12248-010-9183-3
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