Rufloxacin Eyedrops: Effect of Different Formulations on Ocular Pharmacokinetics in Rabbits

PURPOSE

To evaluate the aqueous humor pharmacokinetics of rufloxacin in rabbits after topical administration of different formulations, and to individuate the ones showing the best pharmacokinetic profile.

METHODS

Six formulations were instilled in rabbit eyes: two pH 7.2 suspensions of non-salified rufloxacin base, or zwitterion (RUF), one of which was viscosized with tamarind seed polysaccharide (TSP); two pH 7.2 solutions of RUF obtained using hydroxypropyl-beta-cyclodextrin (CD), one of which was viscosized with TSP; and two pH 5.0 solutions of rufloxacin hydrochloride (RUF-HCl ), one of which was viscosized with TSP. At different times after administration, samples of aqueous humor were withdrawn and analyzed by high-pressure liquid chromatography. The main pharmacokinetic parameters of RUF in the aqueous humor produced by the different formulations were calculated and statistical differences were assessed.

RESULTS

The best results, in terms of aqueous humor bioavailability, were observed with two TSP-viscosized formulations: a solution of the hydrochloride (TSP/RUF-HCl) and a suspension of the base (TSP/RUF), followed by the non-viscosized solution of RUF-HCl. The formulations containing CD-solubilized RUF were much less effective.

CONCLUSIONS

The present data confirm the significant availability-enhancing properties of tamarind seed polysaccharide, and indicate that solubilization of RUF with hydroxypropyl-beta-cyclodextrin (CD/RUF) results in decreased drug availability with respect to standard formulations. Two of the TSP-viscosized formulations (RUF suspension and RUF-HCl solution) produced aqueous humor RUF concentrations in the range of activity against Enterobacteriaceae and Pseudomonas aeruginosa, thus warranting further studies on applications of rufloxacin in ocular therapy.

Poloxamer 407 microspheres for orotransmucosal drug delivery. Part II: In vitro/in vivo evaluation

Aim of this research was to evaluate novel microspheres based on poloxamer 407, alone or in mixture with Gelucire(®) 50/13, as possible buccal delivery system for atenolol (AT). The microspheres have been prepared by spray congealing and investigated to assess AT in vitro delivery through cellulose membranes and ex vivo permeation using porcine buccal mucosa. The microparticles were tested as such or directly compacted to obtain tablets. For comparison the physical mixtures, tablets of the physical mixtures and an AT solution were examined. Finally, the microparticles were sublingually administered in rabbits to evaluate AT pharmacokinetics compared to a market oral tablet (reference). The AT release from microspheres through the synthetic membrane was delayed with respect to the drug solution, more markedly when microparticles contained poloxamer as unique adjuvant; this formulation enhanced AT transmucosal permeation. The enhancement effect of poloxamer was confirmed by the permeation experiments on the corresponding physical mixture. Tabletting hindered both release through cellulose membranes and transmucosal permeation of drug. In vivo studies revealed that the absolute bioavailability of microsphere formulations was higher than that of reference in spite of a lower dosage of drug, suggesting a possible dose reduction by AT microparticles orotransmucosal administration.

Hydrosoluble medicated nail lacquers: in vitro drug permeation and corresponding antimycotic activity

BACKGROUND

Two nail lacquers, containing ciclopirox (CPX) or amorolfine (MRF), based on water-insoluble polymers are currently considered mainstays of topical treatment of onychomycosis. The present study aimed at evaluating the antimycotic activity of a new water-soluble nail lacquer containing CPX (CPX/sol), easily removable by washing with water and applicable to periungual skin.

OBJECTIVES

To compare transungual permeation of CPX with that of MRF in the same hydroxypropyl chitosan-based nail lacquer (MRF/sol) and with a nonwater-soluble reference (Loceryl); Galderma International, La Défense, France), and to evaluate the antimycotic activity of CPX/sol and Loceryl against the most common fungal strains that cause onychomycosis. Methods In vitro drug permeation experiments with CPX/sol, MRF/sol and Loceryl were carried out through bovine hoof slices. Experimental permeates from CPX/sol and Loceryl underwent in vitro susceptibility testing against clinical isolates of dermatophytes, moulds and yeast. Results MRF transungual flux from MRF/sol lacquer was significantly higher when compared with Loceryl. CPX was able to permeate hoof membranes more easily compared with MRF. CPX and MRF concentrations in the subungual fluids collected after application of CPX/sol or Loceryl were sufficient to inhibit fungal growth, with the exception of Candida parapsilosis. Smaller amounts of fluid containing CPX were required for complete inhibition of fungal growth. Efficacy index values were significantly higher for CPX/sol. Conclusions Application of the CPX/sol nail lacquer allows rapid nail penetration of CPX, providing CPX levels sufficient to inhibit fungal growth for a prolonged period of time (30 h) after application of lacquer dose. CPX/sol nail lacquer appeared superior to the market reference Loceryl in terms of both vehicle (hydroxypropyl chitosan) and active ingredient (CPX) as witnessed by its higher efficacy on all nail pathogens.

Niaouli oils from different sources: analysis and influence on cutaneous permeation of estradiol in vitro

Previous studies in vitro had identified niaouli essential oil (NEO) as a valuable transdermal permeation promoter for estradiol (ES). Subsequent considerations on the complex issue of NEO provenance and composition stimulated the present investigation, which was aimed at defining the composition of NEOs obtained from four different sources, at evaluating their influence on transdermal permeation of ES through hairless mouse skin, and at formulating and evaluating simpler terpene mixtures mimicking the NEOs' composition. While all oils contained 1,8-cineol (eucalyptol) as the main component, appreciable variations in composition could be evidenced, originating differences on the ES cutaneous permeation. Two artificial mixtures containing the same proportions of the main terpenes present in each oil (except the commercially unavailable gamma-terpineol) proved equal or significantly superior in activity when compared with the original oils. It is felt that this study might contribute to the formulation of terpene mixtures acting more efficiently and reproducibly with respect to natural NEOs, whose complex and variable composition, depending on growing place, season, and extraction process, is well documented in the relevant literature.

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.

Ocular toxicity of some corneal penetration enhancers evaluated by electrophysiology measurements on isolated rabbit corneas

The influence on electrical resistance and membrane potential of rabbit corneas in vitro of some chemicals used as adjuvants in ophthalmic formulations was investigated, in the attempt to correlate changes in electrophysiological properties of the corneal tissue (possibly indicative of toxic/damaging effects to the corneal epithelium), with the promoting effect of the substances on transcorneal permeation in vitro of timolol maleate (TM). The chemicals, tested at different concentrations, were benzalkonium chloride (BAC), sodium ethylenediaminetetraacetate (EDTA), polyoxyethylene-20-stearyl ether (PSE), polyethoxylated castor oil (PCO), deoxycholic acid sodium salt (DC) and cetylpyridinium chloride (CPC). For these substances, definite correlations were found between promoting activity for permeation of TM and modification of electrophysiological parameters. These parameters were in all cases significantly altered by all agents at all concentrations after a 5-h contact. However, after a 1-h contact, 0.001% PSE and CPC did not significantly modify the corneal resistance, while PCO and PSE did not significantly modify the transcorneal potential at the tested concentrations. Only 0.001% PSE, a nonionic surfactant used as solubilizer and emulsifier, active as promoter for TM, did not modify both electrophysiological parameters to a significant extent after 1 h. The results of this study indicate correlations between ocular toxicity, promoting activity for transcorneal permeation of timolol and modification of the electrophysiological parameters.

Effect of iontophoresis on transcorneal permeation 'in vitro' of two beta-blocking agents, and on corneal hydration

Purpose of the present investigation was to examine the effect of iontophoresis on permeation of two beta-blocking agents, timolol maleate (TM) and betaxolol hydrochloride (BX) across rabbit corneas in vitro. Continuous or pulsed current of variable intensity and duration was applied, and possible corneal damage due to the electric treatment was assessed by measuring the corneal hydration level. The effect of iontophoresis on corneal permeation of the relatively more hydrophilic TM was much greater than the effect on the more lipophilic BX. It was found that for both drugs the iontophoretically driven transcorneal penetration is governed only by current density and overall time of treatment, irrespective of the type of treatment (single or repeated) and of current (constant or pulsed). For both drugs all significant permeation increases due to iontophoresis were invariably accompanied by a significant increased corneal hydration, indicative of damage to the corneal epithelium. Even if the present in vitro data cannot be extrapolated to an in vivo treatment, they confirm the potential risk associated with ocular iontophoresis.

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.

Increased corneal hydration induced by potential ocular penetration enhancers: assessment by differential scanning calorimetry (DSC) and by desiccation

The corneal toxicity of some surfactants of possible use as ocular penetration enhancers was investigated by measuring their effect on hydration of rabbit corneas 'in vitro'. The tested substances were benzalkonium chloride (BAC), cetylpyridinium chloride (CPC), ethylenediaminetetraacetic acid disodium salt (EDTA), polyoxyethylene-20-stearyl ether (Brij 78, PSE), polyethoxylated castor oil (Cremophor EL, PCO) and sodium deoxycholate (DC). Freshly excised corneas, mounted in perfusion cells, were kept in contact for 1 h with solutions of these agents; corneal hydration was then evaluated by measuring: (a) their total (free+bound) water content by desiccation (gravimetric analysis); and (b) their free water content by differential scanning calorimetry (DSC). The DSC measurements also provided a rough quantitative estimate of corneal solutes. All tested agents significantly influenced corneal hydration, evidently as a consequence of alteration of the corneal epithelium. Although a brief contact with the precorneal tissues 'in vivo' may not prove harmful, the use of these compounds as potential ocular permeation enhancers or otherwise as ingredients of topical ocular formulations for long-term use should be considered with caution.

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.

Relevance of polymer molecular weight to the in vitro/in vivo performances of ocular inserts based on poly(ethylene oxide)

A previous study of the present authors on gel-forming erodible inserts, based on high molecular weight (MW, 400 kDa) poly(ethylene oxide) (PEO), for ocular controlled delivery of ofloxacin (OFX) has been extended to investigate the effects of PEO MW, in the 200-2000 kDa range, on insert properties relevant to therapeutic efficacy. Mucoadhesion has shown a dependence on MW, with a maximum for PEO 400. The in vitro drug release from inserts based on PEO 200, PEO 400 and PEO 900 was mainly controlled by insert erosion, whereas with PEO 2000 it was mainly diffusion-controlled in a first phase, followed by an erosion-controlled phase. The erosion time scale depended directly on MW. Immediately after application in the lower conjunctival sac of the rabbit eye, the inserts based on PEO of whichever MW formed mucoadhesive gels, well tolerated by the animals; then the gels spread over the corneal surface and eroded. PEO 2000 was unsuitable as an insert material, since the resulting gel spilled from the eye, due to excessive swelling. The gel residence time in the precorneal area, the drug permanence time in the aqueous humor at concentrations > MIC and the time to reach the maximal drug concentration in the aqueous humor (C(max)) depended directly on MW, indicating that transcorneal absorption was governed by gel erosion. All inserts increased Cmax and AUCeff (AUC for concentrations > MIC) with respect to the commercial eyedrops. The increases caused by PEO 400 and PEO 900 were similar (3.78- and 3.16-fold, respectively, for Cmax; 11.06- and 12.37-fold, respectively, for AUCeff), whereas smaller increases were produced by PEO 200. The PEO 400 and PEO 900 inserts have shown a potential for a topical treatment of endophthalmitis.

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.

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.

Xyloglucan as a novel vehicle for timolol: pharmacokinetics and pressure lowering activity in rabbits

This study was aimed at verifying the performances of a mucoadhesive polysaccharide from tamarind seed (xyloglucan or TSP, tamarind seed polysaccharide) as an adjuvant for ophthalmic vehicles containing timolol. Three formulations (one experimental vehicle based on TSP and two reference commercial eye drops) containing 5 mg/ml timolol base equivalents were administered to the eyes of pigmented rabbits. Drug concentrations in tear fluid, cornea, iris-ciliary body, aqueous humor and plasma were determined, as well as intraocular pressure. The polymer under investigation, in spite of a comparatively low viscosity, produced high timolol concentrations in the ocular tissues and a low systemic absorption. The performances of the TSP vehicle were comparable to those of a reference "in situ" gelling formulation (Timoptic XE). The results point to TSP as a potentially useful adjuvant for ophthalmic delivery systems.

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.

Pharmacokinetics and anti-inflammatory activity in rabbits of a novel indomethacin ophthalmic solution

The formulation of aqueous ophthalmic solutions containing indomethacin (IND) presents serious problems due to poor solubility and stability of the drug. The purpose of this study was to evaluate a novel 0.1% IND formulation containing a poly(oxyethylene)-poly(oxypropylene) block copolymer (poloxamer 407) as solubilizer. This formulation was evaluated for stability, bioavailability and anti-inflammatory activity in comparison with an ophthalmic IND solution currently on the market. The experimental solution, tested for IND stability at different temperatures, compared favorably with the commercial solution. In rabbits, it produced significantly higher IND levels in the aqueous humor and, in an immunogenic uveitis model, it induced a comparatively faster resolution of the symptoms, as determined by inflammation scores and by IOP measurements. The data indicate poloxamer 407 as a potentially valuable nonirritating, solubilizing and stabilizing agent for indomethacin.

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.

Prolonged, contemporaneous administration of pilocarpine and timolol increases the aqueous humor pilocarpine levels in rabbits

The purpose of this study was to gather information on the mechanism by which timolol/pilocarpine (TI/PI) combination eyedrops provide additive ocular hypotensive effects. An hypothesis, according to which the combination eyedrops prolong the intraocular permanence of PI as a consequence of decreased aqueous humor secretion induced by TI, was not supported by clear-cut literature evidence. It was thus sought to verify if repeated instillations in albino rabbits of combination TI/PI eyedrops do effectively prolong the turnover of PI. Commercial eyedrops containing 0.68% w/v TI maleate and 2.0% w/v PI hydrochloride, buffered at pH 6.8, and two reference solutions containing PI hydrochloride alone (2% w/v), buffered at pH 5.5 and 6.8, were instilled b.i.d. in albino rabbits for five days. Aqueous humor samples, analyzed after the last treatment, showed that the aqueous humor PI levels observed after administration of the combination eyedrops were significantly higher than those resulting from administration of the reference formulations. When compared with the pH 6.8 reference solution, the pH 5.5 one produced slightly higher and more sustained drug levels in the aqueous humor. The present results appear to confirm the assumption that an increased retention of PI in the aqueous humor is responsible for the additive effects on intraocular pressure reported by several authors for the combination TI/PI eyedrops.

Silicone rubber/hydrogel composite ophthalmic inserts: preparation and preliminary in vitro/in vivo evaluation

The present report describes the development and in vitro/in vivo testing of rod-shaped mucoadhesive ophthalmic inserts fitting the upper or lower conjunctival fornix. Cylindrical devices (diameter 0.9 mm, length 6-12 mm, weight 3-8 mg) all containing 0.8 mg oxytetracycline HCl (OXT) were prepared from appropriate mixtures of silicone elastomer, OXT and sodium chloride as release modifier. A stable polyacrylic acid (PAA) or polymethacrylic acid (PMA) interpenetrating polymer network (IPN; 30 or 46% w/w) was grafted onto the inserts' surface by treatment with a mixture of acrylic (or methacrylic) acid and ethylene glycol dimethacrylate in xylene at 100 degrees C. Mucoadhesion studies in vitro showed that the mucoadhesive properties increased significantly with increasing thickness of the IPN layer. The inserts were tested for drug release in vitro, and for drug release and retention in rabbit eyes. The presence of IPN, as well as of NaCl, in general increased the drug release rate. The PMA-grafted devices released OXT at lower rates when compared with the PAA-grafted ones. A nearly zero-order release rate for about 1 week was observed in vitro for some types of inserts. When tested in rabbits, some IPN-grafted inserts maintained in the lacrimal fluid a OXT concentration of 20-30 microg/ml for several days: the in vitro minimum inhibitory concentration values (MIC 90%) of OXT against micro-organisms responsible of common ocular infections range from 0.8 to 2.0 microg/ml, while MIC 90% values in the range 14-50 microg/ml have been indicated for Pseudomonas aeruginosa. The ocular retention of IPN-grafted samples was significantly higher with respect to ungrafted ones. The presently described mucoadhesive silicone inserts might prove efficient therapeutic systems for chemotherapy of ocular bacterial infections, such as trachoma.

Ocular mini-tablets for controlled release of timolol: evaluation in rabbits

Topical delivery of timolol by inserts or similar controlled-release devices may offer distinct advantages over administration by eyedrops. The purpose of this investigation was the evaluation in rabbits of ophthalmic inserts (denominated mini-tablets, MT) for sustained/controlled release of timolol maleate (TiM). The MTs (diameter 3.5 mm, thickness 1.5 mm, average TiM content 0.34 or 0.68 mg) were prepared by compressing appropriate mixtures of powders with a standard tabletting machine. A thin, rate-controlling membrane was applied over the devices by spraying aqueous dispersions of acrylic copolymers. A first series of different (uncoated and coated) MTs were tested for release of TiM to the lacrimal fluid, using commercial eyedrops (Timoptol 0.5%) as a reference standard. Two MTs (one of which was coated) and the same reference solution were then selected for an ocular absorption study. Analysis of TiM in the aqueous humor indicated that the coated MT was capable of maintaining low and steady levels of TiM for at least 19 h, while the other device, identical but uncoated, produced a prolonged-pulse effect lasting about 8 h. The apparent mean residence time (MRT) of TiM in the aqueous humor was 1.3 h for the reference solution, 3.2 h for the uncoated MT, and 5.7 h for the coated one. The present preliminary results point to the potential validity of coated mini-tablets as simple systems for controlled ocular delivery of timolol.

Effect of suleparoide on fibrinolysis in the anterior chamber of rabbits

Intra-ocular fibrin deposition following ocular surgery is a serious postoperative complication. The current management of severe postoperative fibrin response is usually ineffective. A quantitative model of fibrin deposition in the rabbit anterior chamber was used to assess the efficacy of Suleparoide I.N.N. (HHS-5) in preventing fibrin formation and in promoting the clearance of fibrinous membranes. Citrated human plasma was injected intracamerally after paracentesis to induce the formation of fibrin clots: 10 min or 24 h after plasma injection, solutions of HHS-5 at different concentrations were injected into the anterior chamber of rabbits. Intra-ocular HHS-5 injection 10 min after plasma injection prevented the formation of fibrinous membranes in a dose-dependent fashion in almost all treated animals. When HHS-5 was injected at 24 h after fibrin clot formation, a reduction of clot areas was observed but the membranes did not completely disappear. No evidence of ocular toxicity was detected by slit-lamp biomicroscopy, intra-ocular pressure and corneal thickness measurements. On the basis of the results obtained with the present animal model, HHS-5 appears as an effective and safe agent for the prevention of fibrinous membrane formation. The data suggest a potential use of HHS-5 for the prophylaxis of fibrin formation in human eyes undergoing extensive intraocular surgery, or in diabetic patients where a hypercoagulable state may be present.

Mucoadhesive ophthalmic vehicles: evaluation of polymeric low-viscosity formulations

A series of polyanionic natural or semi-synthetic polymers (polygalacturonic acid, hyaluronic acid, carboxymethylamylose, carboxymethylchitin, chondroitin sulfate, heparan sulfate and mesoglycan) were evaluated as potential mucoadhesive carriers for ophthalmic drugs. Solutions containing cyclopentolate (CY) or pilocarpine (PI) as salts (or polyanionic complexes) with the acidic polymers, all showing a low viscosity, were tested for miotic (resp. mydriatic) activity in albino rabbits. In the case of some polymeric complexes, small but significant increases of the areas under the activity vs. time curves (AUC) over reference cyclopentolate hydrochloride (CYHC1) or pilocarpine nitrate (PINO3) vehicles, and significant AUC decreases after removal of precorneal mucin by treatment with N-acetylcysteine were observed. A correlation was found between these data, considered indicative of the occurrence of a mucoadhesive interaction "in vivo", and "in vitro" viscometric data expressing the polymers-mucin force of interaction. The advantages and limitations of the mucoadhesive non-viscous approach in the formulation of ophthalmic vehicles are presented and discussed.

Influence of drug release rate on systemic timolol absorption from polymeric ocular inserts in the pigmented rabbit

There is an expectation that ocular inserts, regardless of the nature of the polymer, will faithfully reduce systemic drug absorption. This may not necessarily be so, however, since not all polymers would release drug at the same rate and to the same extent. The objective of the present study was to determine how drug release rate from various polymeric ocular inserts may influence systemic timolol absorption in the pigmented rabbit. The inserts tested were made of polyvinyl alcohol (PVA), hydroxypropylcellulose (HPC), or partial ethyl ester of poly(vinyl methyl ether/maleic anhydride) (PVMMA), approximately 89.4% w/w in all cases. Some polyvinyl alcohol inserts contained timolol in salt form with Carbopol 940 (PVA-C940), 8.6% w/w. The time course of timolol in plasma over 6 hr was monitored using reversed phase HPLC. While all inserts reduced the peak timolol concentration in plasma (Cmax), only the PVA and HPC inserts, which released timolol rapidly in vitro, reduced the extent of systemic timolol absorption (AUC). On the other hand, both PVA-C940 and PVMMA inserts, which released timolol relatively slowly in vitro, increased the extent of systemic timolol absorption. Moreover, the time at which peak timolol concentration was achieved in the plasma was much delayed, raising the possibility of delayed timolol absorption until discharge of the presumably viscous and/or mucoadhesive solutions of PVA-C940 and PVMMA inserts into the nasal cavity. It may be concluded that not all polymeric ocular inserts reduce systemic timolol absorption. Whether an insert would do so depends on the interplay of residence time in the conjunctival sac and rate of drug release from the insert.

Preliminary evaluation of a series of amphiphilic timolol prodrugs: possible evidence for transscleral absorption

A series of amphiphilic esters of timolol malonate (octanoyl, decanoyl, dodecanoyl, myristoyl and palmitoyl timolol) were tested in rabbits for their capacity to antagonise the isoproterenol-induced ocular hypotension, using timolol maleate as reference standard. The most active prodrug, palmitoyl timolol malonate (PTM) was also evaluated for its capacity: (a) to decrease IOP in a model of bethamethasone-induced ocular hypertension, and (b) to permeate "in vitro" through rabbit corneal tissues. PTM, the prodrug with the longest aliphatic chain and therefore the greatest amphiphilic/lipophilic character, showed "in vivo" significant activity differences with respect to timolol maleate: the beta-antagonism was more important at earlier and later experimental times, and the IOP decrease was more marked at longer times. The prodrug, however, showed "in vitro" an inferior corneal permeability when compared with timolol maleate. The significant differences observed for the beta-antagonism of PTM at earlier times of the test might be attributed to transscleral absorption, due to the physicochemical characteristics of the prodrug, while the prolonged action (also observed in the IOP-depression test) might be due to sustained release, resulting from accumulation of the prodrug in the corneal epithelium. The present preliminary results are indicative of the potentiality of amphiphilic properties in a prodrug molecule.

Intraocular pressure reduction and systemic absorption of timolol after administration of one side-coated inserts in rabbits

The object of this study was to test whether flat, circular ophthalmic inserts releasing drug only from one side, would show improved activity parameters and reduced systemic absorption. To this purpose, uncoated and one-side coated hydroxypropylcellulose inserts containing timolol were prepared and evaluated. An acrylic copolymer (Eudragit RS) was used as coating material. Timolol release from inserts was studied both in vitro and in vivo. Timolol release in vitro from the coated inserts was much slower than from the uncoated ones, due to the smaller releasing surface area. Compared with timolol eyedrops (0.5%, 50 microliters), administration of 250 micrograms of timolol in uncoated or coated inserts produced a significantly greater hypotensive effect at 6 and 8 hr post instillation in rabbits with artificially increased intraocular pressure. The coated inserts containing 62.5 micrograms of timolol antagonised isoproterenol-induced ocular hypotension significantly more than timolol eyedrops (0.5%, 12.5 microliters) and uncoated inserts containing 62.5 micrograms of timolol. Both uncoated and coated inserts provided a significant sustaining of timolol release in tear fluid and decreased systemic peak concentrations of timolol with respect to the eyedrop control. However, one-side coated inserts failed to show significant improvements with respect to the uncoated samples.

Vehicle effects in ophthalmic bioavailability: an evaluation of polymeric inserts containing pilocarpine

A series of polymeric ophthalmic inserts containing pilocarpine were formulated with four different types of polyvinyl alcohol, PVA, and two types of hydroxypropylcellulose. Pilocarpine was present as the nitrate, or as the salt with polyacrylic acid, PAA. In-vivo miosis vs time experiments on albino rabbits, showed that all inserts increased significantly the bioavailability of pilocarpine, with respect to a standard solution of pilocarpine nitrate. Two PVA inserts, containing the PAA-salt of pilocarpine, were particularly effective. The preparations were also submitted to in-vitro release tests and to differential scanning calorimetry, to ascertain the release mechanism, and to verify, via the thermal behaviour, possible interactions between drug and polymers. The chemical and physiochemical factors, most likely to influence the ophthalmic bioavailability of pilocarpine from the present preparations, are briefly reviewed.