Susi Burgalassi

Solid lipid nanoparticles (SLN) as ocular delivery system for tobramycin

Aim of this study was to evaluate solid lipid nanoparticles (SLN) as carriers for topical ocular delivery of tobramycin (TOB). The SLN were in the colloidal size range (average diameter below 100 nm; polydispersity index below 0.2) and contained 2.5% TOB as ion-pair complex with hexadecyl phosphate. The preocular retention of SLN in rabbit eyes was tested using drug-free, fluorescent SLN (F-SLN): these were retained for longer times on the corneal surface and in the conjunctival sac when compared with an aqueous fluorescent solution. A suspension of TOB-loaded SLN (TOB-SLN) containing 0.3% w/v TOB was administered topically to rabbits, and the aqueous humour concentration of TOB was determined up to six hours. When compared with an equal dose of TOB administered by standard commercial eyedrops, TOB-SLN produced a significantly higher TOB bioavailability in the aqueous humour.

Evaluation of muco-adhesive properties and in vivo activity of ophthalmic vehicles based on hyaluronic acid

Abstract A series of prospective ophthalmic vehicles based on hyaluronic acid (HA) and on polyacrylic acid (PAA) (solutions, gels, matrices prepared by compression and by casting) containing pilocarpine (Pi) or tropicamide (Tr) was evaluated for muco-adhesion, for ocular retention and for biological activity (miosis, mydriasis) in rabbits. The muco-adhesive properties were investigated in vitro using a tensile apparatus with mucin-coated surfaces, while the ocular behaviour was estimated visually, using vehicles containing a fluorescent marker. Good to excellent muco-adhesive properties were detected in the HA preparations. The bioavailability-enhancing effect, however, was not very satisfactory with Pi, probably on account of the high solubility and diffusivity of the drug. The effect was more evident with the less soluble drug Tr. The validity of the method used for evaluating bioadhesion, and the relevance of the physicochemical characteristics of the drug to a muco-adhesive ocular delivery system are discussed.

Development and in vitro/in vivo testing of mucoadhesive buccal patches releasing benzydamine and lidocaine

Mucoadhesive patches releasing topical drugs in the oral cavity at a slow, predetermined rate may present distinct advantages over traditional dosage forms such as mouthwashes, oral gels and lozenges. The present study was concerned with the preparation and evaluation of mucoadhesive buccal patches for controlled release of benzydamine (BNZ) and lidocaine (LDC). The drugs were used as hydrochlorides, or, to reduce their solubility and improve their release characteristics, as salts with pectin or polyacrylic acid. A LDC-tannic acid complex was also prepared and tested. After an initial screening of mucoadhesive polymers, tamarind gum (TG), a polysaccharide obtained from the seeds of Tamarindus indica, was selected as the adhesive component. In vitro tests, carried out on a cell line of human buccal epithelial origin, indicated a very low sensitivity for TG. The patches, prepared by compressing appropriate mixtures containing the drug salts/complexes, lactose and TG, were tested in vitro for mucoadhesion and drug release, and in vivo on human volunteers for retention and release of BNZ. The devices containing the salts of BNZ with pectin and polyacrylic acid, and the complex of LDC with tannic acid showed zero-order release kinetics in vitro. The patches adhered for over 8 h to the upper gums of the volunteers, and were perfectly tolerated. BNZ hydrochloride was released in vivo and in vitro with practically identical profiles.

Gel-forming erodible inserts for ocular controlled delivery of ofloxacin

A new application of high molecular weight (400 kDa) linear poly(ethylene oxide) (PEO) in gel-forming erodible inserts for ocular controlled delivery of ofloxacin (OFX) has been tested in vitro and in vivo. Inserts of 6 mm diameter, 20 mg weight, medicated with 0.3 mg OFX, were prepared by powder compression. The in vitro drug release from inserts was mainly controlled by insert erosion. The erosion time scale was varied by compounding PEO with Eudragit L100 (EUD) 17% neutralized (EUDNa17) or 71% neutralized (EUDNa71). The insert erosion rate depended on the strength of interpolymer interactions in the compounds, and on the hydrophilic-hydrophobic balance of compounds. Immediately after application in the lower conjunctival sac of the rabbit eyes, the inserts based on plain PEO, PEO-EUDNa17 or PEO-EUDNa71 formed mucoadhesive gels, well tolerated by the animals; then the gels spread over the corneal surface and eroded. The gel residence time in the precorneal area was in the order PEO-EUDNa71 < PEO < PEO-EUDNa17. Compared to commercial OFX eyedrops, drug absorption into the aqueous humor was retarded by the PEO-EUDNa71 inserts, and both retarded and prolonged by the PEO-EUDNa17 inserts, while C(max) (maximal concentration in the aqueous) and AUC(eff) (AUC in the aqueous for concentrations > MIC) were barely altered by either insert type. On the other hand, C(max), AUC(eff) and t(eff) (permanence time in the aqueous at concentrations > MIC) were strikingly increased by plain PEO inserts with respect to commercial eyedrops (5.25 +/- 0.56 vs. 1.39 +/- 0.05 microg ml(-1); 693.6 vs. 62.7 microg ml(-1) min; and 290 vs. 148 min, respectively). Bioavailability increase has been ascribed to PEO mucoadhesion and/or increased tear fluid viscosity.

Development of a Simple Dry Eye Model in the Albino Rabbit and Evaluation of Some Tear Substitutes

The present paper is concerned with the development of a simple dry eye model in the rabbit, induced by daily repeated instillations of 1.0% atropine sulphate. The evolution of the dry eye syndrome in the animals was assessed by the Schirmer I test and by examination of the cornea after fluorescein staining. The model produced rapidly some typical dry eye symptoms and could be satisfactorily used for a preliminary assessment of the protective activity of some polymeric tear substitutes. These were based on hydroxypropylmethylcellulose, sodium hyaluronate, sodium polyacrylate or tamarind gum. The latter polymer showed the best overall results. Ferning tests on the formulations were also performed: their validity as predictors of the efficacy of tear substitutes is discussed.

Cytotoxicity of potential ocular permeation enhancers evaluated on rabbit and human corneal epithelial cell lines

A series of prospective ocular permeation enhancers, benzalkonium chloride (BAC), cetylpyridinium chloride (CPC), ethylenediaminetetraacetic acid (EDTA), polyoxyethylene (20) stearyl ether (PSE) and polyethoxylated castor oil (PCO) were tested for cytotoxicity on cultures of rabbit (RCE) and human (HCE) corneal epithelial cells. The cells were treated for 5,15 and 60 min with different concentrations of the test substances, in serum-free medium and in medium containing 15% foetal bovine serum (FBS). The cytotoxicity was evaluated by WST-1 test. The EC(50) values for HCE, after 15 min exposure and in the presence of FBS, indicate the following order of cytotoxicity: PSE> or =BAC>CPC>EDTA>PCO. After 1 h exposure the order of decreasing cytotoxicity was PSE> or =BAC>CPC>PCO>EDTA. In all cases the presence of FBS appeared to exert a protective effect against the cytotoxic effect.

In vitro transungual permeation of ciclopirox from a hydroxypropyl chitosan-based, water-soluble nail lacquer.

Commercial antimycotic nail lacquers are commonly based on water-insoluble resins. The present study was aimed at evaluating a novel, experimental nail lacquer (P-3051, Polichem SA, Lugano, Switzerland) based on the water-soluble film-forming agent hydroxypropyl chitosan (HPCH). The in vitro permeation of ciclopirox (CPX) from P-3051 and from a commercial, water-insoluble lacquer based on a vinyl resin (Penlac™, Aventis Pharma), was investigated using thin membranes obtained from bovine hooves, an accepted model for human nails. Similar CPX permeation fluxes at steady state through the membranes, but significantly different lag times were observed for P-3051 and Penlac™, when these were tested as dry films. The formulations thus appeared to influence only the time required by CPX to saturate the membrane, and not the final drug concentration gradient in the membrane. Permeation experiments performed on the same membranes and on hairless mouse skin with P-3051 and with a similar, HPCH-free vehicle (ERV), both tested in liquid form, disproved the possibility that HPCH might act as a permeation enhancer for CPX in either substrate. The possible reasons for the greater efficiency of the HPCH vehicle in terms of CPX transfer from the vehicle itself to the keratin membrane are discussed. This effect might be tentatively attributed to a particular affinity of HPCH for the membrane, resulting in intimate contact and strong adhesion of the HPCH lacquer to the keratin substrate.

Effect of chitosan on in vitro release and ocular delivery of ofloxacin from erodible inserts based on poly(ethylene oxide)

The effects of chitosan hydrochloride (CH-HCl) on in vitro release of ofloxacin (OFX) from mucoadhesive erodible ocular inserts and on the relevant ocular pharmacokinetics have been studied both to contribute evidence of the ability of CH-HCl to enhance transcorneal penetration of drugs and to increase the therapeutic efficacy of topically applied OFX. Circular inserts of 6 mm in diameter, 0.8-0.9 mm in thickness and 20 mg in weight, medicated with 0.3 mg drug, were prepared by powder compression. The addition of 10, 20 or 30% medicated CH-HCl microparticles, obtained by spray-drying, to formulations based on poly(ethylene oxide) of MW 900 kDa (PEO 900) or 2000 kDa (PEO 2000) produced changes in the insert microstructure which accelerated both insert erosion and OFX release from inserts. The effect was stronger with higher CH-HCl fractions. Of the CH-HCl-containing formulations based on either PEO 900 or PEO 2000, PEO 900-CH-HCl (9:1 w/w) was more suitable for a prolonged OFX release. Following insertion in the lower conjunctival sac of the rabbits eye, such an insert produced no substantial increase of AUC(eff) (AUC in the aqueous humour for concentrations >MIC(90%)) with respect to inserts based on plain PEO; however, it produced a concentration peak in the aqueous significantly higher than that produced by any of the CH-HCl-free PEO inserts, and well higher than the MIC(90%) for the more resistant ocular pathogens (7 microg/ml vs. 4 microg/ml). It has been argued that the increase was due to the ability of CH-HCl to enhance the transcorneal permeability of the drug.

Comparison of the effect of ultrasound and of chemical enhancers on transdermal permeation of caffeine and morphine through hairless mouse skin in vitro.

The effect of ultrasound (US) on permeation of two model drugs, caffeine (CAF) and morphine (MOR), through hairless mouse skin in vitro was compared with that of three chemical enhancers. Low-frequency (40 KHz), low-power (<0.5 W/cm(2)) US was used; the effect of high-frequency US (1.5-3.0 MHz) was also evaluated in the case of CAF. The chemical enhancers, tested in combination with propylene glycol (PG), were benzalkonium chloride (BAC) oleyl alcohol (OA) and alpha-terpineol (TER). The high-frequency US enhancement of CAF transdermal flux was not statistically significant, while low frequency produced a small but significant increase of the enhancement factor. The effect of US on CAF permeation, however, was lower than that produced by chemical enhancers, in particular OA. The effect of low-frequency US on permeation of MOR was significantly greater (about 10-fold) when compared, on the same frequency and intensity basis, with the effect on CAF. The most active chemical enhancer for MOR, OA, had practically the same effect as low-frequency US. Sonicated skin, although showing slight histological changes, recovered its original low permeability characteristics after turning off sonication. Within the tested system, chemical enhancement appears to offer some advantages over low-frequency US.

Effect of different terpene-containing essential oils on permeation of estradiol through hairless mouse skin.

Purpose of the present investigation was to evaluate six terpene-containing essential oils for their capacity to promote permeation of estradiol (ES) through hairless mouse skin in vitro. Tests on cajuput, cardamom, melissa, myrtle, niaouli and orange oil, all used at the 10% w/w concentration in propylene glycol (PG), evidenced niaouli oil (NIA) as the best permeation promoter for ES. Tests on the main terpene components of NIA (1,8 cineole, alpha-pinene, alpha-terpineol and D-limonene), evaluated neat (10% w/w in PG) or in admixture, confirmed the better promoting activity of whole NIA. The present data point to the validity of complex terpene mixtures, such as that composing NIA, as transdermal penetration enhancers for moderately lipophilic drugs like ES.