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.

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.

Phytochemical investigation of the aerial parts of Sanchezia nobilis Hook. family Acanthaceae has yielded matsutake alcohol (1-octen-3-ol) (1) and four matsutake alcohol glycosides identified as 3-O--glucopyranosyl-1-octen-3-ol (2), 3-O--glucopyranosyl-(16)--glucopyranosyl-1-octen-3-ol (3), 3-O--arabino-pyranosyl-(16)--glucopyran-osyl-1-octen-3-ol (4), and 3-O--arabino-pyranosyl-(16)--glucopyranosyl-(16)--glucopyranosyl-1-octen-3-ol (5). The structures of the isolated compounds were assigned on the basis of different techniques of NMR spectral analysis. Compounds 1–4 have been isolated here for the first time from the family Acanthaceae, while compound 5 is isolated here for the first time from a natural source.

Montelukast (MKST) is a leukotriene receptor antagonist that has been concomitantly used with inhaled corticosteroids (ICS) for its steroid-sparing effect in the long-term management of asthma. However, the simultaneous determination of MKST, when used as ICS tapering therapy, with ICS in human plasma has not yet been reported. A fast and efficient reversed phase monolith HPLC method was developed for simultaneous determination of MKST with some ICS in plasma of asthmatic patients. The separation was achieved on monolith reversed phase column by isocratic mode at a flow rate of 1.0 ml min−1 using a mobile phase consisted of a mixture of acetonitrile and 10 mM phosphate buffer adjusted to pH 3.5 (40:60, v/v) and detected at 240 nm. Betamethasone dipropionate (BDP) was used as the internal standard. All the studied ICS and MKST were efficiently separated within less than 6 min. The obtained linearity range for the developed HPLC method was 0.03-10 µg ml−1 with correlation coefficients > 0.9995 and the detection limits were 0.009-0.016 µg ml−1 in plasma for all the studied drugs. The method was validated in agreement with the requirements of US-FDA guideline and was recommended for the target applications. The method is valuable for investigations concerned with the effective tapering of ICS therapy with MKST in patients with chronic asthma in clinical practice without loss of asthma control.

Montelukast (MKST) is a leukotriene receptor antagonist that has been concomitantly used with inhaled corticosteroids (ICS) for its steroid-sparing effect in the long-term management of asthma. However, the simultaneous determination of MKST, when used as ICS tapering therapy, with ICS in human plasma has not yet been reported. A fast and efficient reversed phase monolith HPLC method was developed for simultaneous determination of MKST with some ICS in plasma of asthmatic patients. The separation was achieved on monolith reversed phase column by isocratic mode at a flow rate of 1.0 ml min−1 using a mobile phase consisted of a mixture of acetonitrile and 10 mM phosphate buffer adjusted to pH 3.5 (40:60, v/v) and detected at 240 nm. Betamethasone dipropionate (BDP) was used as the internal standard. All the studied ICS and MKST were efficiently separated within less than 6 min. The obtained linearity range for the developed HPLC method was 0.03-10 µg ml−1 with correlation coefficients > 0.9995 and the detection limits were 0.009-0.016 µg ml−1 in plasma for all the studied drugs. The method was validated in agreement with the requirements of US-FDA guideline and was recommended for the target applications. The method is valuable for investigations concerned with the effective tapering of ICS therapy with MKST in patients with chronic asthma in clinical practice without loss of asthma control.

Vitamin K homologues are highly lipophilic compounds that require long separation times on chromatographic analysis which does not meet the demand of higher sample throughputs in quality control laboratories. Therefore, this study aimed to develop a new validated high-throughput high-performance thin-layer chromatographic (HPTLC) method to quantify vitamin K homologues including phylloquinone (PK, vitamin K1), menaquinone-4 (MK-4, vitamin K2), and menaquinone-7 (MK-7, vitamin K2). The densitometric analysis was carried out using HPTLC silica gel G 60 F254 plates as the stationary phase. The plates were developed with methanol-ethanol-isopropanol-water (75:5:5:15, v/v/v/v) in the absorbance mode at 254 nm. The retention factors of MK-4, PK, and MK-7 were 0.56, 0.43, and 0.23, respectively. Linearity was found to be in the range of 1-200 ng band1 for PK and MK-4 and 2-200 ng band1 for MK-7 with correlation coefficient of 0.9990 or more. The limits of detection and quantitation were 0.19-0.85 and 0.76-2.5 ng band1, respectively. The method was validated in accordance ICH guidelines. The method was applied for determination of vitamin K homologues in pharmaceutical formulations and food samples after extraction without prior clean-up procedures. The developed HPTLC method provides a useful tool for rapid and efficient high-throughput analysis of vitamin K homologues.