Microemulsions are promising drug delivery systems for ocular delivery of drugs, especially water insoluble drugs such as diclofenac in its acid undissociated form. Microemulsions are characterized with high surfactant content (> 10% w/w) in order to lower the interfacial tension which facilitates dispersion process during the preparation of microemulsion and provides a flexible film around the droplets. However, there are a few researches that have studied the possible irritation effect of microemulsion on the eye. Therefore, evaluation of the ocular irritancy is an important requirement in the development of ocular delivery vehicles such as microemulsions. Draize test using rabbits was used for evaluation of the ocular irritation potential of the prepared microemulsions. The efficacy of the anti-inflammatory action of the formulation showing the least Draize score was then evaluated using 3% croton oil in 2-ethoxyethanol to induce corneal inflammation in rabbits. Results showed that the tested formulations, M5 and M6, were non irritant (NI) where they showed a Draize score of 8 and 14 respectively. When M5 was studied for its anti-inflammatory action and compared with marketed eye drops, Epifenac, it showed a significantly shorter recovery time compared to Epifenac eye drops.

Conventional dosage forms such as eye drops are the most used dosage form by ocular route, in spite of their low bioavailability and the pulsed release of the drug where it is expected that direct application of the drug to the eye will give maximum response; however after instillation of an eye drop, about 70% of the administered volume can be seen to be lost by different factors. For this reason new ocular drug delivery vehicles have been developed in order to minimize the amount of the drug lost from the eye and at the same time provide maximum response with reduced frequency of administration. Among such delivery systems are microemulsions. Microemulsions are a promising dosage form for ophthalmic application because their industrial production and sterilization are relatively simple and inexpensive; they have good thermodynamic stability and inherently provide the capacity to make soluble lipophilic drugs. At the same time, 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 microemulsion and acting as drug reservoir, on the cornea and thus increasing the time in which the drug is available for absorption. This review will discuss the important characteristics of ocular delivery systems, factors that reduce drug availability to the eye and methods to improve ocular bioavailability. It will also focus on microemulsions, their preparation methods, their components and their applications as drug carrier for ocular use.

Conventional dosage forms such as eye drops are the most used dosage form by ocular route, in spite of their low bioavailability and the pulsed release of the drug where it is expected that direct application of the drug to the eye will give maximum response; however after instillation of an eye drop, about 70% of the administered volume can be seen to be lost by different factors. For this reason new ocular drug delivery vehicles have been developed in order to minimize the amount of the drug lost from the eye and at the same time provide maximum response with reduced frequency of administration. Among such delivery systems are microemulsions. Microemulsions are a promising dosage form for ophthalmic application because their industrial production and sterilization are relatively simple and inexpensive; they have good thermodynamic stability and inherently provide the capacity to make soluble lipophilic drugs. At the same time, 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 microemulsion and acting as drug reservoir, on the cornea and thus increasing the time in which the drug is available for absorption. This review will discuss the important characteristics of ocular delivery systems, factors that reduce drug availability to the eye and methods to improve ocular bioavailability. It will also focus on microemulsions, their preparation methods, their components and their applications as drug carrier for ocular use.

Conventional dosage forms such as eye drops are the most used dosage form by ocular route, in spite of their low bioavailability and the pulsed release of the drug where it is expected that direct application of the drug to the eye will give maximum response; however after instillation of an eye drop, about 70% of the administered volume can be seen to be lost by different factors. For this reason new ocular drug delivery vehicles have been developed in order to minimize the amount of the drug lost from the eye and at the same time provide maximum response with reduced frequency of administration. Among such delivery systems are microemulsions. Microemulsions are a promising dosage form for ophthalmic application because their industrial production and sterilization are relatively simple and inexpensive; they have good thermodynamic stability and inherently provide the capacity to make soluble lipophilic drugs. At the same time, 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 microemulsion and acting as drug reservoir, on the cornea and thus increasing the time in which the drug is available for absorption. This review will discuss the important characteristics of ocular delivery systems, factors that reduce drug availability to the eye and methods to improve ocular bioavailability. It will also focus on microemulsions, their preparation methods, their components and their applications as drug carrier for ocular use.

Diclofenac is a synthetic, non-steroidal anti-inflammatory and analgesic compound. It is used topically to treat many inflammatory ocular conditions. However, the poor aqueous solubility of its acidic undissociated form, Diclofenac acid (DA), limits its use. As a result, it is used in the form of eye drops containing its salt form, diclofenac sodium (DNa), which has a short duration of action due to its solubility in tears which leads to its rapid drainage from the eye and the patient has to administer it frequently. In light of this, the objective of the present study was to design microemulsion systems for ophthalmic delivery of water insoluble drug, DA. DA-loaded microemulsion was prepared using isopropyl myristate (oil phase), Tween 80 (surfactant), glycerin (co-surfactant) and Sörensen isotonic phosphate buffer pH 7.4 (aqueous phase). Characterization of the prepared formulations including viscosity, pH, particle size analysis, and stability studies were also performed. The pH of the formulations varied within the range of 6.8 and 7.4. The mean droplet size for all formulations of microemulsion was found in the range of 220-480 nm. The formulations showed a sustained release of DA up to 24 h.

Diclofenac is a synthetic, non-steroidal anti-inflammatory and analgesic compound. It is used topically to treat many inflammatory ocular conditions. However, the poor aqueous solubility of its acidic undissociated form, Diclofenac acid (DA), limits its use. As a result, it is used in the form of eye drops containing its salt form, diclofenac sodium (DNa), which has a short duration of action due to its solubility in tears which leads to its rapid drainage from the eye and the patient has to administer it frequently. In light of this, the objective of the present study was to design microemulsion systems for ophthalmic delivery of water insoluble drug, DA. DA-loaded microemulsion was prepared using isopropyl myristate (oil phase), Tween 80 (surfactant), glycerin (co-surfactant) and Sörensen isotonic phosphate buffer pH 7.4 (aqueous phase). Characterization of the prepared formulations including viscosity, pH, particle size analysis, and stability studies were also performed. The pH of the formulations varied within the range of 6.8 and 7.4. The mean droplet size for all formulations of microemulsion was found in the range of 220-480 nm. The formulations showed a sustained release of DA up to 24 h.