G. Di Colo

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.

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.

Is dialysis a reliable method for studying drug release from nanoparticulate systems?-A case study.

The kinetics of in vitro drug release from nanoparticulate systems is extensive, though uncritically, being studied by dialysis. Evaluating the actual relevance of dialysis data to drug release was the purpose of this study. Diclofenac- or ofloxacin-loaded chitosan nanoparticles crosslinked with tripolyphosphate were prepared and characterized. With each drug, dynamic dialysis was applied to nanoparticle dispersion, solution containing dissolved chitosan·HCl, and solution of plain drug. Drug kinetics in receiving phase (KRP), nanoparticle matrix (KNM) and nanoparticle dispersion medium (KDM) were determined. Release of each drug from nanoparticles was also assessed by ultracentrifugation. Although KRP data may be interpreted in terms of sustained release from nanoparticles, KNM and KDM data show that, with both drugs, the process was in fact controlled by permeation across dialysis membrane. Analysis of KRP data reveals a reversible interaction of diclofenac with dispersed nanoparticle surface, similar to the interaction of this drug with dissolved chitosan·HCl. No such interactions are noticed with ofloxacin. The results from the ultracentrifugation method agree with the above interpretation of dialysis data. This case study shows that dialysis data from a nanoparticle dispersion is not necessarily descriptive of sustained-release from nanoparticles, hence, if interpreted uncritically, it may be misleading.

Antibodies to a new viral citrullinated peptide, VCP2: fine specificity and correlation with anti‐cyclic citrullinated peptide (CCP) and anti‐VCP1 antibodies

Anti‐citrullinated protein/peptide antibodies (ACPA) are a hallmark of rheumatoid arthritis (RA) and can be measured using different citrullinated substrates. In this paper we describe a new viral citrullinated peptide – VCP2 – derived from the Epstein–Barr virus‐encoded protein EBNA‐2 and analyse its potential as substrate for ACPA detection. Analysing sera from 100 RA patients and 306 controls, anti‐VCP2 immunoglobulin (Ig)G were found in 66% of RA sera, IgM in 46% and IgA in 39%, compared with less than 3% of control sera. Anti‐VCP2 IgG was associated with erosive arthritis, the presence of rheumatoid factor and anti‐VCP1 and anti‐cyclic citrullinated peptide (CCP) antibodies. Anti‐VCP2 antibodies were detected in 1% and anti‐VCP1 antibodies in 4% of CCP‐negative RA sera; conversely, 3% of the VCP‐negative sera were CCP‐positive. Taken together, these data suggest that VCP2 could offer a valuable tool for ACPA detection. Inhibition assays showed that two non‐overlapping epitopes – a citrulline–glycine stretch shared between VCP1 and VCP2 and the N‐terminal portion of the VCP2 sequence – were targeted by anti‐VCP2 antibodies. Moreover, in some RA sera that tested positive in CCP and VCP2 assays, preincubation with VCP2 inhibited binding to CCP, whereas in other sera the binding was unaffected. Thus, the reactivity with more than one ACPA substrate might be due in some RA patients to antibody populations with different specificities, and in others to cross‐reactive antibody populations. Finally, affinity‐purified anti‐VCP2 antibodies immunoprecipitated deiminated Epstein–Barr virus nuclear antigen (EBNA‐2) from an EBNA‐2‐transfected cell line, suggesting that viral sequences may be involved in the generation of the ACPA response.

Silicone microspheres for pH-controlled gastrointestinal drug delivery

Silicone microspheres containing pH-sensitive hydrogels are prepared, characterized and evaluated for their potential pH-controlled gastrointestinal (GI) drug delivery. The pH-sensitive hydrogels are semi-interpenetrating polymer networks (semi-IPN(s)) made of varying proportions of poly(methacrylic acid-co-methylmethacrylate) (Eudragit (EUD) L100 or EUD S100) and crosslinked polyethylene glycol 8000 (P8000C). Up to 35 wt% hydrogel particles of mean volume diameters from 89 to 123 microm, medicated with 15 wt% prednisolone (PDN), are encapsulated, with 100% efficiency, into morphologically acceptable silicone microspheres in the 500-1000 microm size range, by a modified emulsion vulcanization method. Microspheres are eluted for 9 h with isotonic fluids at pH values increasing from 1.2 to 7.4, to simulate transit across the GI regions. PDN release depends on dissolution medium pH and on hydrogel composition, which determines hydrogel pH-sensitivity. With the P8000C-EUD L100 (1:2) semi-IPN, the release shows a marked peak at pH 6.8. The P8000C-EUD S100 (1:2) semi-IPN causes a gastroprotection and an almost uniform distribution of released drug between media at pH 6.8 and 7.4. With the P8000C-EUD S100 (1:1) semi-IPN, the dose fraction released to gastric fluid increases to match the values for the media at pH 6.8 and 7.4. With the pH-insensitive, highly swelling, P8000C, the largest dose fraction is released to the gastric medium and release is of Fickian type. With semi-IPNs, release depends weakly on the buffer molarity of the dissolution medium, a reduction from 0.13 to 0.032 of which renders the release rate to the media at pH 6.8 and 7. 4 more uniform.

In vitro evaluation of a pH-sensitive hydrogel for control of GI drug delivery from silicone-based matrices

Abstract The release of drugs having very different aqueous solubilities and partitioning properties, such as salicylamide (SAM), nicotinamide (NAM), clonidine·HCl (CHC) and prednisolone (PDN), from 1 mm thick silicone discs containing, in dispersion, around 35 wt% medicated granules of a pH-sensitive hydrogel, is studied in vitro. The hydrogel is a poly(acrylic acid) (PAA):poly(ethylene oxide) interpenetrating polymer network (IPN). The matrices are eluted with simulated GI fluids, i.e., with a medium of pH 1.2 for 2 h, followed by a medium of pH 6.8 for 2 h, followed by a medium of pH 7.4 for 5 h. The release rate pattern is always bimodal and is determined by the pH-dependent swelling of the IPN granules in matrix. In simulated gastric fluid (SGF) the IPN swelling degree is low and the release is limited to an initial burst, followed by a rapid decline. In simulated intestinal fluid (SIF), PAA in the IPN becomes ionized, the IPN swelling degree increases and the release rate rises to a second maximum. The drug fraction released is always preponderant in SIF compared to SGF. The matrix swelling and drug release rates are influenced by the granule size. With a loading dose of 5 wt% in IPN granules in the 355–425 μm size range, SAM, NAM and PDN show the same release rates in SIF. Differences arise when the load is raised to 20 wt% and/or the granule size range is reduced to 105–250 μm. CHC shows an ionic interaction with PAA in the IPN, which limits the release rate in SIF. The release of drugs not ionically interacting with PAA is virtually uninfluenced by ample variations in osmolality, ionic strength and buffer molarity of dissolution medium.

Vehicle effects on in vitro skin permeation of and stratum corneum affinity for model drugs caffeine and testosterone

The effects of Labrasol (LBS) (glycolysed ethoxylated C8/C10 glycerides), Labrafil (LBF) (glycolysed ethoxylated glycerides), Transcutol (TSC) (diethylene glycol monoethyl ether) and DPPG (propylene glycol dipelargonate) on the flux across excised human skin of the lipophilic testosterone (TST) and the hydrophilic caffeine (CAF) and on the affinity of the human stratum corneum for these drugs are compared taking propylene glycol (PG) and liquid petrolatum (LP) as reference vehicles. DPPG and LBF enhance CAF flux relative to PG while LBS and TSC increase the stratum corneum affinity for TST relative to LP. However, the materials tested enhance neither the flux of nor the stratum corneum affinity for both drugs with respect to either reference. On the other hand, a saturated solution of DPPG in PG enhances both properties for both drugs relative to PG. Such effects are ascribed to the ability of DPPG to interact with the lipid bilayers and to that of PG to promote DPPG penetration into stratum corneum and to create interaction sites in such a tissue.

Drug release from silicone elastomer through controlled polymer cracking: an extension to macromolecular drugs

Abstract An attempt to promote macromolecule release at controlled rates from a polydimethylsiloxane elastomer (Silastic Q7-4840) through osmotically induced osmotically active granules in the 40–106,106–150 or 150–212 μm size range, composed of bovine serum albumin (BSA) and sodium chloride in a 35:65 or 70:30 w/w ratio. The latter granule composition was found to be unsuitable, due to an inadequate level of osmotic agent. With the 35:65 w/w BSA-NaCl ratio in granules protein release to normal saline is of zero-order in the matrix swelling stage. The stationary release rate and time scale are modulated through matrix geometry and granule load and size. With disk-shaped devices and 106–150 or 150–212 μm granule size the release rate and granule load are linked by a log-log correlation. The release pattern is determined by the rate of polymer cracking. The solutes are carried through cracks by a composite convective-diffusive flux.

In vitro evaluation of a system for pH-controlled peroral delivery of metformin

Oral absorption of the antihyperglycaemic agent metformin (MF x HCl) is confined to the upper part of the intestine, therefore controlled-release oral formulations of this drug should ensure a complete release during transit from stomach to jejunum. Compressed matrix tablets based on pH-sensitive poly(ethylene oxide) (PEO)-Eudragit L100 (EUD L) compounds have shown in vitro a compliance with the above requirement. The polymer compounds were prepared by a coevaporation process. The release pattern of MF x HCl from matrices depended on the PEO-EUD L ratio in the coevaporate. The 1:1 (w/w) ratio was unable to control MF x HCl release in simulated gastric fluid (SGF, pH 1.2), because the matrix material was excessively hydrophilic. Nevertheless, the release rate in SGF could be modulated by increasing the EUD L fraction in the coevaporate. With a PEO (M(w), 400 kDa)-EUD L (1:2, w/w) ratio the percent dose released in 2 h to SGF, where the coevaporate was insoluble, was around 23 or 50% with 10 or 20% loading dose. The release was then completed within the successive 2 h of elution with simulated jejunal fluid (SJF, pH 6.8) where EUD L and the coevaporate gradually dissolved. Release in SGF was controlled by matrix swelling and/or drug diffusion in matrix, whereas matrix dissolution controlled release in SJF. The unique release-controlling properties of the polymer compounds were due to PEO-EUD L macromolecular interactions. Matrices show promise of a gradual and complete release of MF x HCl from stomach to jejunum, unaffected by gastric pH fluctuations. This mode of administration might allow the use of lower therapeutic doses compared to existing immediate- or sustained-release products, thus minimising side effects.

A study of release mechanisms of different ophthalmic drugs from erodible ocular inserts based on poly(ethylene oxide).

When topical controlled delivery of ophthalmic drugs is realised via erodible inserts, drug bioavailability is maximised, if release is controlled exclusively by insert erosion, since parallel mechanisms which increase the release rate, also increases the dose fraction cleared from the precorneal area by tear fluid draining. The respective contributions of diffusion and erosion to the release mechanism of different drugs, namely, prednisolone (PDS), oxytetracycline hydrochloride (OTH) and gentamicin sulfate (GTS), from erodible ocular inserts based on poly(ethylene oxide) (PEO) of molecular weight 400 or 900kDa was determined by an in vitro technique adequate to predict the release mechanism in vivo. PDS and OTH were released with erosion-controlled kinetics. With therapeutic doses of these drugs in the inserts (0.3mg, 1.5%), the possibility of a purely erosive mechanism was shown to rely upon drug-PEO molecular interactions, which limit drug diffusion in the swollen matrix. This was the case with OTH, for which strong interactions with PEO were measured, whereas some contribution from the parallel diffusive mechanism was evidenced for PDS, which showed weaker interactions with polymer. Such a contribution disappeared when the PDS concentration in the insert was increased to 6%, which suggested that the erosive mechanism is favoured by a drug concentration in the hydrated insert substantially higher than solubility. On the other hand, the release of about 50% GTS dose was controlled by diffusion, due to the high water solubility of this drug, accompanied by weak drug-PEO interactions. In this case the residence time of drug in the precorneal area is expected to be significantly shorter than that of the PEO carrier.