Ocular Inserts - The Final Say in Ocular Drug Delivery?


Ocular drug delivery is where drugs are directly administered to the eye via injections/eye drops. It is one of the most challenging aspects of ocular pharmacology. Patients requiring injections have to go out of their way to attend uncomfortable procedures at outpatient clinics. The efficacy of eye drops is dependent on the patient’s skills, but even the perfect placement of eye drops will only result in 1-10% of the total administered dose being absorbed. These cons are responsible for low patient compliance, and consequently worse outcomes than predicted. After 20 years of trialling new ocular drug vehicles, ophthalmic pharmacies have devised ocular inserts as a novel solution. Their administration is speedier and more comfortable for the patient, they ensure better drug absorption at a regular rate, and they don’t have to be replaced as frequently.


Ocular inserts are thin, drug-impregnated devices placed into the cul-de-sac or conjunctival sac of the eye. They can release steroids to treat eye inflammation, they can release antibiotics for infections, or even nanoparticles to treat glaucoma.


There are multiple types of ocular inserts in production: Insoluble (diffusion, osmotic, soft-contact lenses), and soluble (natural polymers or synthetic polymers). The insert with the best prospects is the soft-contact lens - simply a hydrophilic contact lens soaked in a drug solution, however its rate of delivery isn’t as precise as other methods listed.

The drug can be released via diffusion, osmosis, or simply bio-erosion - where the implant is eroded by tears/eye movements, and the drug is released.


Ocular inserts have advantages over other models of ocular drug administration into the eye - such as increased time in situ and longer, sustained release of a medication. Currently in the UK there is only one drug that the BNF recognises as deliverable via ocular inserts: Mydriasert - A mixture of phenylephrine hydrochloride and tropicamide. The benefit of this over eye drops is clear: Longer lasting mydriatic effects with minimal irritation. But no current model is perfect, none of them possess all the advantages, and they each come with their own set of disadvantages:


Advantages

  • Better patient compliance
  • Drug dosing is accurate and can be released at a slow, regular rate
  • Can target internal ocular tissues through non-corneal routes (e.g. conjunctival-scleral route)
  • Increased ocular residence = more drug gets absorbed
  • Less inflammatory than other ocular drug vehicles
Disadvantages

  • The solid insert can be perceived as uncomfortable in oversensitive patient’s eye
  • Unintentional loss of drug when sleeping/rubbing eye
  • Interference with vision
  • Difficult to remove if they migrate to the upper fornix

These limitations are fixable, research is now looking into tweaking the materials, bespoke design, and dimensions of inserts to improve their fit to the conjunctival sac.


Currently ocular inserts aren’t commercially favoured due to their cost for fabrication, a single dose of steroids via this route is estimated to cost the patient $589. However, one study has shown that in the long run, when demand increases and more efficient manufacturing techniques are employed, drugs such as Olopatadine Hydrochloride are cheaper in an insert form as they don’t require an excipient to be administered in addition.


Data collection for comparing ocular inserts to other drug vehicles is slow because patients are reluctant to have experimental devices placed somewhere as sensitive as their eyes. However, the story is far from over. Pharmacists haven’t been resting on their laurels after inventing this novel ocular drug vehicle; They have been perfecting it, and indeed, in 2018, the FDA approved the use of Dextenza (a steroid ophthalmic insert) to treat ocular pain after ophthalmic surgeries. As the technology advances, use of inserts is going to become even more common in everyday practice.


Written by Gabriel Bellamy Plaice


References

1. Kumari A, Sharma PK, Garg VK, Garg G. Ocular inserts - Advancement in therapy of eye diseases. J Adv Pharm Technol Res [Internet]. 2010 Jan 7 [cited 2021 Oct 24];1(3):291. Available from: https://www.japtr.org/article.asp?issn=2231-4040;year=2010;volume=1;issue=3;spage=291;epage=296;aulast=Kumari;type=0

2. Independent T. FDA approves Dextenza (dexamethasone ophthalmic insert) for the treatment of ocular pain following ophthalmic surgery [Internet]. FDA approves Dextenza (dexamethasone ophthalmic insert) for the treatment of ocular pain following ophthalmic surgery | theindependentbd.com. [cited 2021 Oct 24]. Available from: https://www.theindependentbd.com/arcprint/details/179157/2018-12-17

3.   Topical ocular drug delivery: recent developments and future challenges - PubMed [Internet]. [cited 2021 Oct 24]. Available from: https://pubmed.ncbi.nlm.nih.gov/3332284/

4. Dextenza Prices, Coupons & Patient Assistance Programs [Internet]. Drugs.com. [cited 2021 Oct 24]. Available from: https://www.drugs.com/price-guide/dextenza

5. Qureshi J, Iqbal FM, Hussain F, Ijaz H, Aamir MF, Afzal M. Fabrication and evaluation of Olopatadine hydrochloride ocular inserts. J Plast Film Sheeting [Internet]. 2020 Jul 1 [cited 2021 Oct 24];36(3):243–59. Available from: https://doi.org/10.1177/8756087920911423

6. Excellence N-TNI for H and C. BNF: British National Formulary - NICE [Internet]. NICE; [cited 2021 Jan 31]. Available from: https://bnf.nice.org.uk/drug/misoprostol.html


Image credit: Figure 3 The application of nanotechnology to ophthalmic devices. The... [Internet]. ResearchGate. [cited 2021 Oct 24]. Available from: https://www.researchgate.net/figure/The-application-of-nanotechnology-to-ophthalmic-devices-The-sustained-release-of-drug_fig2_343465565

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