Zimei Wu

Conjunctival and corneal tolerability assessment of ocular naltrexone niosomes and their ingredients on the hen's egg chorioallantoic membrane and excised bovine cornea models.

This study aimed at combining the hens egg test-chorioallantoic membrane (HET-CAM), bovine corneal opacity and permeability (BCOP) test and histological examination of excised corneas to evaluate the conjunctival and corneal toxicity of niosomes and their ingredients. Various surfactant/lipid combinations and concentrations (1-10%, w/v) were investigated for the ocular delivery of an ambitious drug (naltrexone hydrochloride) for treatment of diabetic keratopathy. Four niosomal formulations were investigated and found to be non irritant to the 10 days old HET-CAMs (an acceptable conjunctival model). Only one of the tested ingredients (sodium cholate - CH) showed moderate irritation, however such an effect was diminished when incorporated into niosomes. Corneal opacity and fluorescein permeability scores for the test substances correlated well with the HET-CAM test results. Corneal erosion and stromal thickness were found to be in agreement with the HET-CAM and BCOP results, which discriminated well between moderately and mildly irritant test substances. Corneal histological examination revealed toxicity signs included epithelial erosion, stromal condensation and stromal vacuolisation, which allowed better discrimination between strong and moderate irritants. It is concluded that the prepared niosomes possess good ocular tolerability and minimal ocular tissue irritation. They can be further investigated as ocular delivery systems using appropriate animal models.

Niosomes and discomes for ocular delivery of naltrexone hydrochloride: morphological, rheological, spreading properties and photo-protective effects.

Naltrexone hydrochloride (NTX) is a promising treatment for corneal disorders linked to diabetes mellitus (diabetic keratopathy). However, NTX has a major stability problem due to autoxidation, which is likely to hinder its formulation as eye drops for treatment of diabetic keratopathy. In this study, in-house developed NTX non-ionic surfactant vesicles (niosomes and discomes) were evaluated for their spreading, rheological properties and their ability to impede the inevitable autoxidation of NTX in aqueous solutions. The measured contact angles and spreading coefficients for niosomes reflected significantly (P<0.05) better wetting and spreading abilities than the aqueous vehicle. The prepared niosomes were significantly more viscous (P<0.05) than the aqueous solution. The lipid content, size and composition of niosomes are the main factors affecting the viscosity of niosomal dispersions. Exposure of NTX solution to artificial daylight illumination (10,000 lux) can produce extensive degradation of NTX due to oxidation. The prepared formulations were able to significantly (P<0.05) protect the encapsulated NTX from the photo-induced oxidation compared with free NTX solutions. The investigated niosomes lend themselves as a potential ocular delivery modality for NTX.

A stability-indicating HPLC assay with diode array detection for the determination of a benzylpenicillin prodrug in aqueous solutions

The aim of this study was to develop a stability-indicating HPLC assay for the determination of penethamate (PNT), an ester prodrug of benzylpenicillin (BP), in aqueous solutions. The method was validated by subjecting PNT to forced decomposition under stress conditions of acid, alkali, water hydrolysis and oxidation. A quenching solution was developed to limit degradation to negligible levels before and during the analysis. Both PNT and BP were simultaneously determined and separated in presence of degradation products on a C(18) column using a mobile phase consisting of methanol-acetonitrile-acetate buffer. Different degradation products were formed in the stress conditions. The peak purity indexes of PNT and BP obtained by diode array detection were >0.999, confirming the absence of other co-eluting substances. The assay was linear for both analytes in the concentration range 1-100 microg mL(-1). The LOD and LOQ of PNT were 0.03 and 0.09 microg mL(-1) respectively. Degradation of PNT followed pseudo-first-order kinetics with t(1/2) of 43.6 min at pH 2.01 and 4.2 min at pH 9.31. In addition, the absence of BP in the acidic solutions of PNT emphasises the futility of monitoring BP to assess the stability of PNT. In conclusion, the assay is rapid and stability-indicating with adequate precision and accuracy, and in conjunction with the quenching solution, can be used for stability studies of PNT with simultaneous quantitation of BP. The degradation studies provide useful information for formulation development of PNT.

Tissue compatibility and pharmacokinetics of three potential subcutaneous injectables for low-pH drug solutions

OBJECTIVESnThe aim of the study was to investigate the tissue tolerance and bioavailability of four formulations containing 5% ricobendazole solubilised at low pH, following subcutaneous injection in sheep. Formulations were: a water-in-oil emulsion, a microemulsion, a hydroxypropyl-beta-cyclodextrin (HP-beta-CD, 20%) drug solution, and a low-pH drug solution (reference).nnnMETHODSnIn-vitro cytotoxicity of the formulations was investigated in L929 fibroblasts using MTS viability and lactate dehydrogenase leakage assays. Each formulation and respective vehicle was injected into either side of the back of a sheep to investigate the tissue tolerance and pharmacokinetics.nnnKEY FINDINGSnIn-vitro studies suggested that both the emulsion and the microemulsion are unlikely to give a burst release of the low-pH drug solution in aqueous media. The microemulsion showed the greatest in-vitro cytotoxic effect but no significant difference was observed between the other formulations. In sheep, the three new formulations and vehicles caused little or no injection-site reactions compared with a marked response to the reference formulation. Bioavailabilities of HP-beta-CD formulation, emulsion and microemulsion formulations, relative to the reference formulation, were 194, 155 and 115%, respectively.nnnCONCLUSIONSnThe three new subcutaneous injectables showed promise for reducing irritation of low-pH solubilised ricobendazole. HP-beta-CD significantly enhanced the drug absorption. Controlling the burst release of the low-pH drug solution may improve tissue tolerance and minimise post-injection precipitation, and hence increase drug bioavailability. The in-vitro cytotoxicity studies did not predict the in-vivo irritation effects.Objectives Our aim was to investigate the effect of etoricoxib on the anticonvulsant activity of phenytoin and diazepam against seizure models in mice. In addition the acute adverse effect of etoricoxib was assessed with a chimney test.

Preformulation characteristics of the opioid growth factor antagonist-naltrexone hydrochloride: stability and lipophilicity studies

In the last twenty years mesoporous materials (e.g., silica, silicon, and to a lesser extent titanium) have been extensively investigated as possible carriers for controlled drug delivery purposes. The great benefits of these materials are their high surface areas and pore volumes with tunable pore sizes and easily functionalized pore surface properties, which allow high drug payloads and from very rapid to slow release kinetics for controlled drug release formulations. The present review focuses on recent research on the exploitation of mesoporous silica and silicon based materials for controlled drug release applications. In particular, fabrication processes of these materials, drug loading and drug release profiles and mechanisms, as well as further functionalization of the porous surface structures of the materials are surveyed. Several examples of drug delivery formulations, together with drug release mechanisms, such as sustained release and stimuli-responsive controlled-release, are also presented herein.

Absorption and tissue tolerance of ricobendazole in the presence of hydroxypropyl-β-cyclodextrin following subcutaneous injection in sheep

Post-injection precipitation may cause poor and erratic drug absorption and tissue irritation at the injection site. Tissue tolerance and pharmacokinetics of a low pH ricobendazole (RBZ) injectable containing 20% hydroxypropyl-beta-cyclodextrin (HP-beta-CD) were simultaneously investigated after subcutaneous injection in sheep compared to a reference formulation without HP-beta-CD. Each animal received a RBZ containing formulation on one side of the back and the respective vehicle on the contralateral side. The HP-beta-CD vehicle showed good tissue tolerance and the acidic solution caused minimal injection site reactions. Both RBZ containing formulations caused pain on injection and tissue histological changes in some animals. Lack of elevation of plasma creatine kinase indicated that none of the formulations caused significant damage to the underlying muscle tissue. Compared to the reference formulation, AUC and C(max) of the HP-beta-CD formulation were 1.6 and 2.2 times higher, respectively, whereas t(max), MRT and t(1/2) were significantly shorter suggesting faster and greater absorption of RBZ in the presence of HP-beta-CD. This was attributed to the effect of inhibition of post-injection drug precipitation and drug absorption enhancement of HP-beta-CD. In conclusion, HP-beta-CD was shown to be a tissue-compatible excipient with potential to inhibit post-injection precipitation and increase absorption of poorly water soluble drugs. Additionally, the HP-beta-CD formulation showed promise as an injectable that potentially minimizes irritation by reducing the dose required.

Stability of ricobendazole in aqueous solutions

The chemical stability of ricobendazole (RBZ) was investigated using a stability-indicating high performance liquid chromatographic (HPLC) assay with ultraviolet detection. The degradation kinetics of RBZ in aqueous solution was evaluated as a function of pH, buffer strength and temperature. The oxidation reaction in hydrogen peroxide solution was also studied. Degradation products were analyzed by mass spectroscopy and degradation pathways are proposed. Degradation of RBZ followed pseudo first-order kinetics and Arrhenius behavior over the temperature range 24-55 degrees C. A V-shaped pH-rate profile over the pH range 2-12 was observed with maximum stability at pH 4.8. The shape of the pH-rate profile was rationalized by catalytic effects of various components in the solution on each RBZ species. At pH 11 the activation energy for hydrolysis was 79.5 kJ/mol, and phosphate catalysis was not observed. Oxidation occurred in hydrogen peroxide solutions and was catalyzed by the presence of copper (Cu(2+)) ions. Ricobendazole amine and albendazole sulfone were identified by MS assay to be the degradation products of hydrolysis and oxidation respectively.

Tissue compatibility and pharmacokinetics of three potential subcutaneous injectables for low-pH drug solutions: Subcutaneous injectables for low-pH drug solutions

Objectivesu2002 The aim of the study was to investigate the tissue tolerance and bioavailability of four formulations containing 5% ricobendazole solubilised at low pH, following subcutaneous injection in sheep. Formulations were: a water‐in‐oil emulsion, a microemulsion, a hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD, 20%) drug solution, and a low‐pH drug solution (reference).

Pre-formulation and chemical stability studies of penethamate, a benzylpenicillin ester prodrug, in aqueous vehicles.

Penethamate (PNT) is a diethylaminoethyl ester prodrug of benzylpenicillin used to treat bovine mastitis via the intramuscular route. Because of its instability, PNT products must be reconstituted before administration and the reconstituted injection has a short shelf life (7 days at 2–8°C). The purpose of this paper was to investigate whether the stability of PNT can be improved in order to achieve a chemically stable ready-to-use aqueous-based PNT formulation or at least to extend the shelf life of the reconstituted suspension. A chemical stability study of PNT in aqueous-based solutions as a function of pH, buffer strength, solvent mixtures and temperature, supported by studies of its solubility in mixed solvents, allowed predictions of the shelf life of PNT solution and suspension formulations. PNT degraded in aqueous solutions by several pathways over the pH range 2.0–9.3 with a V-shaped pH-rate profile and a minimum pH of around 4.5. The stability of PNT solutions in mixed solvents was greater than in aqueous solutions. For example, in propylene glycol:citrate buffer (60:40, v/v, pH 4.5), the half-life of PNT was 4.3 days compared with 1.8 days in aqueous buffer. However, solubility of PNT in the mixed solvent was higher than that in aqueous solution and this had an adverse effect on the stability of suspensions. By judicious choosing of pH and mixed solvent, it is possible to achieve a storage life of a PNT suspension of 5.5 months at 5°C, not sufficient for a ready-to-use product but a dramatic improvement in the storage life of the reconstituted product.

Characterization and evaluation of β-glucan formulations as injectable implants for protein and peptide delivery.

Context: Injectable implants are biodegradable, syringeable formulations that are injected as liquids, but form a gel inside the body due to a change in pH, ions or temperature. Objective: To investigate the effect of polymer concentration, pH, ions and temperature on the gel formation of β-glucan, a natural cell-wall polysaccharide derived from barley, with particular emphasis on two-phase system formation after addition of dextran or PEG. Materials and methods: Oscillation viscometry was used to evaluate the gel character by measuring flow index (N), storage (G′) and loss (G″) moduli. Two-phase systems were further characterized for hardness and syringeability using a texture analyzer. Finally, in vitro release characteristics were determined using Franz diffusion cells. Results: Oscillation viscometry revealed that only addition of dextran or PEG resulted in distinct gel formation. This was seen by a decrease in N after polymer addition. Moreover, hardness (in g) of the gels increased significantly (pu2009<u20090.001) from 3.65u2009±u20090.43 to 34.30u2009±u20098.90 (dextran) and 805.80u2009±u20095.30 (PEG) 24u2009h after polymer addition. In vitro release profiles showed significantly (pu2009<u20090.05) reduced AUC0–8 h, k and percentage of drug released from two-phase systems compared to β-glucan dispersions, with the PEG system resulting in the lowest amount released over 8u2009h (15.1u2009±u20091.6%). Discussion: The unfavorable mixing enthalpy and higher water affinity of PEG resulted in the formation of a dense β-glucan gel. Conclusion: 1.5% (w/w) β-glucan combined with PEG at a ratio of 1:3 seemed to be the most promising injectable formulation with respect to fastest gel formation, increased hardness and sustained release.