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REVIEW ON OCULAR DRUG DELIVERY


Contact lenses
Contact lenses can absorb water-soluble drugs when soaked in drug solutions. These drug-saturated contact lenses are placed in the eye for releasing the drug for a long period of time. The hydrophilic contact lenses can be used to prolong the ocular residence time of the drugs. In humans, the Bionite lens which was made from hydrophilic polymer (2-hydroxy ethyl methacrylate) has been shown to produce a greater penetration of fluorescein. [72]

Figure 9: Contact lenses.

Artificial tear inserts
A rod shaped pellet of hydroxy propyl cellulose without preservative is commercially available (Lacrisert). This device is designed as a sustained release artificial tear for the treatment of dry eye disorders. It was developed by Merck, Sharp and Dohme in 1981. [73]

Figure 10: Artificial tear insert.

Filter paper strips
Sodium fluorescein and rose Bengal dyes are commercially available as drug-impregnated filter paper strips. These dyes are used diagnostically to disclose corneal injuries and infections such as herpes simplex and dry eye disorders.

Figure 11: Fluorescein paper strips.

Microemulsion
Due to their intrinsic properties and specific structures, microemulsions are a promising dosage form for the natural defense of the eye. Indeed, because they are prepared by inexpensive processes through auto emulsification or supply of energy and can be easily sterilized, they are stable and have a high capacity of dissolving the drugs. The in vivo results and preliminary studies on healthy volunteers have shown a delayed effect and an increase in the bioavailability of the drug. The proposed mechanism is based on the adsorption of the nanodroplets representing the internal phase of the microemulsions, which constitutes a reservoir of the drug on the cornea and should then limit their drainage. [74-76]

Figure 12: Microemulsion of ocular delivery.

Ocular inserts
Ocular inserts are solid dosage forms and can overcome the disadvantage reported with traditional ophthalmic systems like aqueous solutions, suspensions and ointments. The ocular inserts maintain an effective drug concentration in the target tissues. Limited popularity of ocular inserts has been attributed to psychological factors, such as reluctance of patients to abandon the traditional liquid and semisolid medications and to occasional therapeutic failures (e.g., unnoticed expulsions from the eye, membrane rupture, etc.). A number of ocular inserts were prepared utilizing different techniques to make soluble, erodible, nonerodible and hydrogel inserts. [77–79] The examples of ocular inserts are given in Table 2.

Figure 13: ocular insert.

Table2: Ocular inserts devices [80–88]

Name

Description

Soluble ocular drug Insert


Small oval wafer, composed of soluble copolymers consisting of actylamide, N-venyl pyrrolidone and ethyl acetate, soften on insertion

New ophthalmic drug delivery system


Medicated solid polyvinyl alcohol flag that is attached to a paper- covered with handle. On application, the flag detaches and gradually dissolves, releasing the drugs


Collagen shields

Erodible disc consist of cross-link porcine scleral collagen

Ocusert


Flat, flexible elliptical insoluble device consisting of two layers, enclosing a areservior, use commercially to deliver Pilocarpine for 7 days

Minidisc or ocular therapeutic

system 4-5 mm diameter contoured either hydrophilic or hydrophobic disc

Lacrisert

Rose-shape device made from Hydroxy propyl cellulose use for the eye syndrome as an alternative to tears


Bioadhesive ophthalmic eye insets

Adhesive rods based on a mixture of Hydroxy propyl cellulose, ethyl cellulose, Poly acrylic acid cellulosephthalate

Dry drops

A preservative free of hydrophilic polymer solution that is freeze dried on the tip of a soft hydrophobic carrier strip, immediately hydrate in tear strip

Gelfoam

Slabs of Gelfoam impregnated with a mixture of drug and cetyl ester wax in chloroform

Collagen shield
Collagen is regarded as one of the most useful biomaterials. The excellent biocompatibility and safety due to its biological characteristics such as biodegradability and weak antigenecity made collagen the primary resource in medical applications. Collasomes show promise among drug delivery systems to the human eye. They are first fabricated from porcine scleral tissue, which bears a collagen composition similar to that of the human cornea. The shields are hydrated before they are placed on the eye, having been stored in a dehydrated state. Typically the drug is loaded into the drug solution for a period of time prior to application. Collagen shields are designed to be inserted in a physician’s office; they often produce some discomfort and interfere with vision. Shields are not individually fit for each patient, as are soft contact lenses and therefore, comfort may be problematic and expulsion of the shield may occur. Kaufman et al have developed a new drug delivery system- collasomes. [89] They combined collagen pieces or particles and a viscous vehicle that could be instilled beneath the eyelid, thereby simplifying application and reducing the blurring of vision. Collasomes were well tolerated; and because the collagen particles are suspended in carrier vehicles, they could be instilled safely and effectively by patients in much the same fashion as drops or ointments.

Figure 14: collagen shield loaded with drug inserted in eye.

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