Patrizia Chetoni

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.

Evaluation of ocular permeation enhancers: In vitro effects on corneal transport of four β-blockers, and in vitro/in vivo toxic activity

Abstract The efficacy and toxicity of a series of prospective ocular penetration enhancers (benzalkonium chloride, EDTA, non-ionic surfactants, surface-active heteroglycosides and bile salts) was investigated in vitro, using isolated rabbit corneas. As test drugs four β-blocking agents were used, chosen in order of increasing lipophilicity: atenolol (AT), timolol (TM), levobunolol (LB) and betaxolol (BX). The increased corneal hydration induced by the enhancers was taken as an index of cellular and tissue damage; the ocular irritancy of the agents was also tested in rabbits in vivo. In the absence of enhancers, the apparent corneal permeability coefficients of the four drugs were in the order AT ⋍ TM

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.

Evaluation of high- and low-molecular weight fractions of sodium hyaluronate and an ionic complex as adjuvants for topical ophthalmic vehicles containing pilocarpine

Ophthalmic vehicle; Hyaluronic acid; Pilocarpine; Miotic test; Ocular permanence test; Rabbit; Bioadhesion Summary Two low-molecular-weight fractions of sodium hyaluronate (Na-HA), denominated Hyalastin® and Hyalectin®, were investigated as potential adjuvants for ophthalmic vehicles containing pilocarpine nitrate (PiN). Tests were also performed on an ionic complex (HA/PiB) prepared from hyaluronic acid (derived from Hyalastin®) and pilocarpine base. The performance of the vehicles under study was verified by miosis and ocular retention tests carried out on albino rabbits, against a series of reference vehicles, three of which contained a high-molecular-weight fraction of Na-HA (Healon®). The group of 14 reference and test preparations exhibited Newtonian or pseudoplastic flow characteristics and encompassed a wide range of apparent viscosities (1 to 1054 mPa s). The results indicate that the HA/PiB salt and the high-MW Na-HA can significantly increase the bioavailability of pilocarpine with respect to reference vehicles of comparable viscosity: an effect that can be reasonably attributed to muco-adhesive effects. Conversely, in the present rabbit tests, the low-MW fractions of Na-HA performed poorly as adjuvants for the PiN solutions.

Pectin microspheres as ophthalmic carriers for piroxicam: evaluation in vitro and in vivo in albino rabbits

Microparticulate polymeric delivery systems have been suggested as a possible approach to improve the low bioavailability characteristics shown by standard ophthalmic vehicles (collyria). Purpose of this study was the evaluation of pectin microspheres as delivery system for piroxicam (Px). The microspheres were prepared by a spray-drying technique; their morphological characteristics were investigated by scanning electron microscopy (SEM), and their in vitro release behavior was evaluated in pH 7.0 USP buffer using a flow-through apparatus. Px loaded in the pectin microspheres showed a faster in vitro dissolution rate with respect to solid micronized drug. The precorneal retention of fluorescein-loaded microspheres was evaluated in vivo in albino rabbits: an aqueous dispersion of fluorescent microspheres showed a significantly increased residence time in the eye (2.5 vs. 0.5 h) when compared with a fluorescein solution. In vivo tests in rabbits of dispersions of Px-loaded microspheres also indicated a significant improvement of Px bioavailability in the aqueous humour (2.5-fold) when compared with commercial Px eyedrops. The potential advantages and limitations of this delivery system are discussed.

Preparation and evaluation in vitro of colloidal lipospheres containing pilocarpine as ion pair

Abstract Aqueous dispersions of solid lipospheres containing up to 7.5% pilocarpine as lipophilic ion pairs were submitted to a preliminary evaluation. The lipospheres (diameter 75–85 nm) consisted mainly of stearic acid and egg lecithin; pilocarpine base was incorporated as ion pair with mono-octylphosphate, monodecylphosphate and monohexade-cylphosphate. The following parameters were investigated: stability constants (β) and lipophilicity of the ion pairs, size, polydispersity and drug content of the lipospheres, pilocarpine release in vitro. The preparations might constitute a promising vehicle for sustained ocular delivery of pilocarpine.