Development of O/W nanoemulsions for ophthalmic administration of timolol.

After an initial screening of ingredients and production methods, nanoemulsions for ocular administration of timolol containing the drug as maleate (TM) or as ion-pair with AOT (TM/AOT) were prepared. The physico-chemical characterization of nanoemulsions, regarding mean diameter, pH, zeta potential, osmolarity, viscosity and surface tension, underlined their feasibility to be instilled into the eyes. Single components and emulsions were tested ex vivo on rabbit corneas to evaluate corneal irritation, that was measured according to opacity test. A marked decrease in corneal opacity was observed using the drug formulated in nanoemulsions rather than in aqueous solutions. Drug permeation and accumulation studies were performed on excised rabbit corneas. An increase in drug permeation through and accumulation into the corneas were observed using TM-AOT compared to TM due to an increase of lipophilicity of the drug as ion-pair. The introduction of chitosan (a positive charged mucoadhesive polymer) into emulsions allowed to increase TM permeation probably due to the interaction of chitosan with corneal epithelial cells.

Hemp-seed and olive oils: their stability against oxidation and use in O/W emulsions.

Hemp-seed oil has several positive effects on the skin: thanks to its unsaturated fatty acid (PUFA) content it alleviates skin problems such as dryness and those related to the aging process. We present a comparative study of hemp-seed and olive oils, determining some physicochemical indices and evaluating their stability against oxidation. The peroxide value of hemp-seed oil was below 20, the threshold limit for edible oils. Hemp-seed oil was less stable against peroxidation than olive oil, but MDA and MONO assays showed its stability to be above expectations. The chlorophyll contained in extra virgin olive oil had a higher photostability than that contained in hemp-seed oil, possibly due to the larger amount of antioxidant in the olive oil. A certain amount of Vitamin E was found in hemp-seed oil. Since quality analyses indicated that hemp-seed oil is relatively stable, emulsions were prepared with the two oils, and their stability and rheological characteristics were tested. Some of the resulting gel-emulsions were suitable for spraying on the skin.

Vitamin A palmitate photostability and stability over time.

Vitamin A palmitate photostability in relation to UVA and UVB was tested in hydroxy ethyl cellulose hydrogels at pH 4.0, 5.6, 7.0, and 8.0, alone and with the addition of sunscreens (3,4-methylbenzilidencamphor or butyl methoxy dibenzoylmethane) or an antioxidant (butylated hydroxy toluene). The photostability of vitamin A palmitate was also tested in encapsulated systems (Tagravit A1 microcapsules, Lipotec liposomes, phosphatidylcholine liposomes, and Lipotec nanocapsules) dispersed in gels at pH 5.6 and 7.0. The stability of retinyl palmitate over time in hydroxy ethyl cellulose hydrogels at pH 5.6 and 7.0 (stored one month at 25 degrees C or 40 degrees C), alone or with butylated hydroxy toluene, was also tested. The stability of retinyl palmitate over time in encapsulated systems, dispersed in gels at pH 5.6 and 7.0, was also studied. O/W emulsions were also prepared to compare the stability of vitamin A palmitate introduced in a lipophilic/hydrophilic medium (O/W emulsions) and a hydrophilic medium (hydrogels). HPLC analysis showed that encapsulated systems such as Lipotec nanocapsules, Tagravit A1 microcapsules, phosphatidylcholine liposomes, and Lipotec liposomes protect the vitamin A ester over time from hydrolysis and from oxidation to retinaldeide and retinoic acid, and that Lipotec nanocapsules and phosphatidylcholine liposomes also improve the vitamin's photostability. A change in pH (from 5.6 to 7.0) of the gels did not influence the vitamin ester's stability. pH levels of 4.0 and 8.0 determined a decrease in the stability of retinyl palmitate in the gels. A high concentration of sunscreens improved the photostability of retinyl palmitate in the gels at pH 5.6 and 7.0. Butylated hydroxy toluene protected retinyl palmitate from degradation induced by light at all the pH levels studied and by heat at pH 5.6 and 7.0, as can be seen from the study of the photostability of vitamin A palmitate under UVB and UVA and of stability over time. Rheological studies showed a slight decrease in the viscosity of the gels after UVB-UVA irradiation and a higher decrease in the viscosity of the gels and the emulsions after storage at 25 degrees C and 40 degrees C. This decrease can be attributed to a partial degradation of hydroxy ethyl cellulose and of emulsifier, as can be seen from the decrease in shear stress versus shear rate values under these conditions of storage, denoting a depolymerization of the rheological modifier.

Photostability of naturally occurring whitening agents in cosmetic microemulsions.

An o/w microemulsion formulated using lecithin and an alkyl glucoside as mild, non-irritant surfactants was proposed as a cosmetic vehicle for arbutin and kojic acid, naturally occurring whitening agents. After assessing the physicochemical stability of the microemulsion in the presence and absence of whitening agents, several perfumed compositions, developed using fragrant molecules of natural or synthetic origin, were introduced, and the olfactory impact of the perfumed microemulsion was evaluated. The photostability to UVB irradiation of both whitening agents was determined in aqueous solutions and in microemulsions, and also in the presence of the perfumed compositions. The stability of arbutin and kojic acid was higher in microemulsions than in aqueous solutions, and only in some cases did the presence of odorous molecules appear to influence it: linalool exerted some protective effect towards kojic acid photodegradation.

Elastic liposomes for skin delivery of dipotassium glycyrrhizinate.

The aim of this study was to evaluate the possibility of using liposomes for skin delivery of dipotassium glycyrrhizinate (KG), an anti-inflammatory agent employed in treating acute and chronic dermatitis, and of formulating such liposomes in an oil-in-water emulsion (O/W). KG had emulsifying properties and the possibility of producing elastic liposomes was verified. Liposomes containing soya lecithin (PC) or hydrogenated soya lecithin (HPC) mixed with KG in w/w ratios of 2:1, 4:1 or 8:1 were prepared by the solvent evaporation method and then passed through a high pressure homogeniser. Liposome size and entrapment efficiency were determined and the interaction between KG and HPC was investigated using differential scanning calorimetry (DSC). Transepidermal permeation through intact pig skin and skin deposition of KG from liposomes and O/W emulsion containing liposomes were assessed and compared with values for aqueous control solutions. No marked differences were observed between PC and HPC liposomes. Liposome sizes ranged from 90 to 120 nm. Entrapment efficiency depended on the lipid:KG ratio; the maximum efficiency was obtained at 4:1 w/w. KG interacted with liposomes disrupting and fluidising the lipid bilayer, forming elastic liposomes able to penetrate through membrane pores of diameter much smaller than their own diameter. The liposome structure was maintained when dispersed in an O/W emulsion. The skin fluxes were less than the HPLC detection limit for all systems, while skin deposition increased 4.5-fold compared with aqueous solutions when KG was formulated in liposomes.

Vitamin A and vitamin A palmitate stability over time and under UVA and UVB radiation.

Vitamin A and vitamin A palmitate photostability were tested in different media. Ethanol and octyl octanoate solutions of these two vitamins, as such and with the addition of sunscreens (3,4 methylbenzilidencanfora, butyl methoxy dibenzoylmethane and octyl methoxycinnamate) or beta-carotene and butylated hydroxy toluene, were analysed spectrophotometrically after UVB or UVA irradiation. An O/W fluid emulsion with 0.5% w/w of retinyl palmitate, with and without butylated hydroxy toluene, was prepared. The oil containing the vitamin was extracted with HCl and aluminium sulfate and analysed spectrophotometrically after UVB or UVA irradiation. The fluid emulsion containing retinyl palmitate with and without butylated hydroxy toluene was stored at different temperatures and analysed every week spectrophotometrically for a month. Of the sunscreens tested butyl methoxy dibenzoylmethane showed the strongest protective action towards vitamin A and vitamin A palmitate, whereas beta-carotene did not protect either vitamin. Butylated hydroxy toluene inhibited the photodegradation of both vitamins dissolved in octyl octanoate, suggesting that oxygen may be involved in their degradation. O/W emulsion promoted slightly the degradation of vitamin A ester. Butylated hydroxy toluene protected retinyl palmitate from degradation induced by light and heat.

Emulsions containing partially water-miscible solvents for the preparation of drug nanosuspensions.

The aim of this study was to investigate the feasibility of partially water-miscible solvents, such as benzyl alcohol, butyl lactate and triacetin, to prepare drug nanosuspensions by a solvent quenching technique. Mitotane, which possesses very poor water solubility and low bioavailability, was used as model drug. Preparation was by emulsifying an organic solution of the drug in an aqueous solution of a stabilising agent followed by rapid displacement of the solvent from the internal into the external phase, provoking solid particle formation. To verify the influence of emulsion droplet size on the drug particle size, 0.1 or 0.2% of different emulsifiers (Tween 80, caprylyl-capryl glucoside or lecithin) and different homogenisation conditions (Ultra Turrax or a high pressure homogenizer at 200 or 1000 bar for three cycles) were used. In general, emulsion droplet size decreased with high pressure homogenization and on increasing the number of cycles. The size of drug particles, obtained after adding water at a constant rate, was dependent on the droplet size in the emulsion. Drug particles of approximately 80 nm were obtained using butyl lactate, supporting the hypothesis that drug particle formation by the emulsification diffusion process involves generating regions of local supersaturation. Because of the increase in available surface area, the dissolution rate of diaultrafiltrated suspensions increased greatly compared to commercial product.

On the stability of ascorbic acid in emulsified systems for topical and cosmetic use.

Several O/W microemulsions, O/W and W/O emulsions and a W/O/W multiple emulsion were prepared using non-ionic, non-ethoxylated, skin compatible emulsifiers. Ascorbic acid (vitamin C) was added to the emulsified systems and its stability against oxidation was studied at 45.0 degrees C in aerobic conditions and compared with that in aqueous solutions at different pH values. All emulsified systems provided protection to ascorbic acid, as its degradation rate, which increased with increasing pH, was slower in emulsified systems than in aqueous solutions. The highest protection of ascorbic acid was when it was dissolved in the inner aqueous phase of the W/O/W multiple emulsion, both at 45 and at 20 degrees C for long storage. A pseudo first-order mechanism was hypothesised for ascorbic acid degradation in the experimental conditions for as long as abundant dissolved oxygen was present.

Investigation of the phase behaviour of systems containing lecithin and 2-acyl lysolecithin derivatives.

A series of modified phospholipids (m-PC) possessing different acyl chains in position 2, from butanoyl to hexadecanoyl, were prepared by partial synthesis from soybean lysolecithin. They were used with soybean lecithin to construct phase diagrams containing ethanol as cosolvent, water and medium chain triglycerides (MCT) or isopropyl myristate (IPM) as oils. The weight ratios lecithin:m-PC and surfactants:ethanol were kept constant at 1:1. The results indicate that the m-PCs have a strong effect on the microemulsion (L) and liquid crystalline (LC) domains in the water-rich/oil-poor part of the phase diagrams, although all diagrams correspond to a single lecithin:m-PC ratio. On decreasing the acyl chain length, and thus increasing the hydrophilicity of the surfactant, there was a corresponding increase in the L area, which moved towards the aqueous corner of the phase diagrams. The LC phase was detected only in the presence of the hexadecanoyl derivative for the systems containing MCT, and it was not detected only in the presence of the butanoyl derivative for the systems containing IPM. The use of a second hydrophilic surfactant to adjust the packing properties of the lecithin-alcohol systems, and/or to increase the fluidity of the surfactant film, increased the region of existence of the isotropic systems. This may be of importance in the formulation of drug delivery systems, especially those which are diluted by biological fluids upon administration.

Inhibition of lipoperoxidation of linoleic acid by five antioxidants of different lipophilicity.

The efficacy of oxidation inhibition of five natural and synthetic antioxidants (BHT, BHA, nordihydroguaiaretic acid (NDGA), quercetin and rutin) was studied in O/W emulsions. Linoleic acid was used as a reference molecule; the reaction was initiated by an azo-compound. The kAH characterizing the reaction of the antioxidant with the peroxyl radical decreases in the following order: kAH(BHA) > kAH(BHT) > kAH(NDGA) > kAH(quercetin) > kAH(rutin).

Calorimetric study on the solubilization of butanol by alkylphosphate and alkylphosphate-lecithin systems.

Microcalorimetric studies on alkylphosphate-butanol and alkylphosphate-butanol-lecithin systems were carried out as a first step to study the role of butanol (used as cosurfactant) in the formation of microemulsions. The enthalpy of solubilization; delta H, of the same amount of butanol (1.806 mol kg-1) in aqueous sodium monoalkyl-phosphates, with a hydrocarbon chain varying from 6 to 10 carbon atoms, was investigated as a function of alkylphosphate concentration. Measurements were performed in the presence and in the absence of lecithin. The enthalpy values measured upon addition of butanol to the mixtures were negative in all cases. Below the critical micelle concentration (CMC) of the alkylphosphates, the heats of butanol dissolution were found to decrease upon increasing the concentration of the alkylphosphate. This behaviour was related to the dissolution of butanol in water and to the formation of mixed butanol-alkylphosphate and butanol-alkylphosphate-lecithin micelles. Above the CMC essentially constant delta H values were found. The delta H measured may be the sum of simultaneous effects--heat of alcohol dissolution and the simple alkylphosphate micelle dissociation or alkylphosphate-lecithin mixed aggregate dissociation and the heat of mixed micelle formation. The delta H at the plateaus were linearly related to the corresponding CMC values of the alkylphosphates.

Microemulsions as topical delivery vehicles: ocular administration of timolol.

The topical administration of timolol as an ion-pair with octanoate was achieved by use of an oil-in-water microemulsion containing lecithin as a surfactant. The microemulsion, a solution of the ion-pair and a solution of timolol alone were instilled in the conjunctival sac of rabbits. A rapid method for the separation and determination of timolol in aqueous humour by HPTLC was used. The bioavailability of timolol from the microemulsion and the ion-pair solution was higher than that obtained from timolol alone. The areas under the curve for timolol in aqueous humour after administration of the microemulsion and the ion-pair solution were 3.5 and 4.2 times higher, respectively, than that observed after the administration of timolol alone.

Influence of chlorpromazine on the accumulation of 5-hydroxytryptamine by interaction with ATP.

5-Hydroxytryptamine accumulates at pH 6.0 when ATP is present on one side of an artificial lipoidal barrier. In the presence of chlorpromazine, the diffusion of ATP through the barrier and a decrease in the accumulation of serotonin can be noted. The diffusion rate constants of ATP and serotonin are related to the concentration of chlorpromazine.