Studies on rifampicin release from ethylcellulose coated nonpareil beads

How wound environments trigger the release from Rifampicin-loaded liposomes

BACKGROUND

Chronic wounds often contain high levels of proinflammatory cytokines that prolong the wound-healing process. Patients suffering from these conditions are likely to benefit from topical rifampicin therapy. Although recent research indicates considerable anti-inflammatory properties of the antibiotic, currently, there are no commercial topical wound healing products available. To address this medical need, a liposomal drug delivery system was developed. A mechanistic investigation outlined major influences of wound environments that affect the release kinetics and, as a consequence, local bioavailability.

METHODS

Liposomes were prepared using the thin-film hydration method and subsequently freeze-dried at the pilot scale to improve their stability. We investigated the influence of oxidation, plasma proteins, and lipolysis on the in vitro release of rifampicin and its two main degradation products using the Dispersion Releaser technology. A novel simulated wound fluid provided a standardized environment to study critical influences on the release. It reflects the pathophysiological environment regarding pH, buffer capacity, and protein content.

RESULTS

During storage, the liposomes efficiently protect rifampicin from degradation. After the dispersion of the vesicles in simulated wound fluid, despite the significant albumin binding (>70%), proteins have no considerable effect on the release. Also, the presence of lipase at pathophysiologically elevated concentrations did not trigger the liberation of rifampicin. Surprisingly, the oxidative environment of the wound bed represents the strongest accelerating influence and triggers the release.

CONCLUSION

A stable topical delivery system of rifampicin has been developed. Once the formulation comes in contact with simulated wound fluid, drug oxidation accelerates the release. The influence of lipases that are assumed to trigger the liberation from liposomes depends on the drug-to-lipid ratio. Considering that inflamed tissues exhibit elevated levels of oxidative stress, the trigger mechanism identified for rifampicin contributes to targeted drug delivery.

Preparation and characterization of emamectin benzoate nanoformulations based on colloidal delivery systems and use in controlling Plutella xylostella (L.) (Lepidoptera: Plutellidae)

Colloidal delivery systems have been widely used as carriers for controlled delivery of pesticides to improve the efficacy and photostability of natural and semi-synthetic pesticides. In this study, we have synthesized emamectin benzoate nanoformulations (EB + NFs) depending on polymeric nanocapsules (PNC) and two types of the nanosilica, mesoporous nanosilica (MCM-48) and silicon dioxide nanoparticles (SNPs) as carriers for the emamectin benzoate (EB). The fabricated nanoformulations were characterized by using X-ray diffraction analysis, Fourier transform infrared spectroscopy, particle size, zeta potential, morphology, absolute recovery (AR), entrapment efficiency (EE), UV stability and release kinetics. The obtained results showed that the carriers had a remarkable loading ability for EB and improved the EB photostability. The EE% of nanoformulations were 92.84%, 87.45% and 71.19% for emamectin benzoate polymeric nanocapsules (EB + PNC), emamectin benzoate SNPs (EB + SNPs) and emamectin benzoate MCM-48 (EB + MCM-48) respectively. The insecticidal activity of EB + NFs against Plutella xylostella showed that the EB + SNPs was more effective than other EB + NFs and EB alone. The LC₅₀ values were 0.18, 4.03, 8.49 and 11.06 mg L⁻¹ for EB + SNPs, EB + MCM-48, EB + PNC and EB respectively. The obtained results suggest the colloidal delivery systems that used in this study could improve the efficacy and photostability for EB, and they are able to overcome the disadvantage of the natural and semi-synthetic pesticides such as environmental sensitivity and to increase the efficacy of pesticides, which eventually leads to reduce the dosage of pesticides needed, reducing the number of applications required in comparison to conventional formulations.

Colloidal delivery systems have been widely used as carriers for controlled delivery of pesticides to improve the efficacy and photostability of natural and semi-synthetic pesticides.

Peculiar effect of polyethylene glycol in comparison with triethyl citrate or diethyl phthalate on properties of ethyl cellulose microcapsules containing propranolol hydrochloride in process of emulsion-solvent evaporation

Plasticizers play a crucial role in various process of microencapsulation. In this study, the effect of incorporation of plasticizer in process of emulsion solvent evaporation was investigated on properties of ethyl cellulose (EC) microcapsules containing propranolol hydrochloride. The effect of plasticizer type and concentration were investigated on characteristics of microcapsules prepared from different viscosity grades of EC. Product yield, encapsulation efficiency, mean particle size, shape, surface characteristics, solid state of drug, and drug release profiles were evaluated. Product yield and encapsulation efficiency were not dependent on plasticizer type and concentration. However, encapsulation efficiency decreased with increase in EC viscosity grade in the most of the cases. The mean particle size was in the range of 724-797 μm and was not dependent on plasticizer type. Microcapsules formed in the presence of PEG had a very smooth surface with few pores. XRD and DSC studies revealed a reduction of drug crystallinity after microencapsulation especially in presence of PEG. The results showed that the presence of TEC and DEP with different concentrations had no marked effect on drug release from microcapsules containing different viscosity grades of EC. This was not the case when PEG was used, and despite its water solubility it reduced the drug release rate noticeably. The reduction in the drug release in the presence of PEG was concentration-dependent. The use of PEG as a plasticizer in process of emulsion solvent evaporation highly improved the EC microcapsule structure and retarded the drug release rate and therefore is recommended.

Supercritical antisolvent co-precipitation of rifampicin and ethyl cellulose

Rifampicin-loaded submicron-sized particles were prepared through supercritical anti-solvent process using ethyl cellulose as polymeric encapsulating excipient. Ethyl acetate and a mixture of ethyl acetate/dimethyl sulfoxide (70/30 and 85/15) were used as solvents for both drug and polymeric excipient. When ethyl acetate was used, rifampicin was crystallized separately without being embedded within the ethyl cellulose matrix while by using the ethyl acetate/dimethyl sulfoxide mixture, reduced crystallinity of the active ingredient was observed and a simultaneous precipitation of ethyl cellulose and drug was achieved. The effect of solvent/CO₂ molar ratio and polymer/drug mass ratio on the co-precipitates morphology and drug loading was investigated. Using the solvent mixture, co-precipitates with particle sizes ranging between 190 and 230nm were obtained with drug loading and drug precipitation yield from respectively 8.5 to 38.5 and 42.4 to 77.2% when decreasing the ethyl cellulose/rifampicin ratio. Results show that the solvent nature and the initial drug concentrations affect morphology and drug precipitation yield of the formulations. In vitro dissolution studies revealed that the release profile of rifampicin was sustained when co-precipitation was carried out with the solvent mixture. It was demonstrated that the drug to polymer ratio influenced amorphous content of the SAS co-precipitates. Differential scanning calorimetry thermograms and infrared spectra revealed that there is neither interaction between rifampicin and the polymer nor degradation of rifampicin during co-precipitation. In addition, stability stress tests on SAS co-precipitates were carried out at 75% relative humidity and room temperature in order to evaluate their physical stability. SAS co-precipitates were X-ray amorphous and remained stable after 6months of storage. The SAS co-precipitation process using a mixture of ethyl acetate/dimethyl sulfoxide demonstrates that this strategy can be successful for controlling rifampicin delivery.

Rifampicin-loaded ‘flower-like’ polymeric micelles for enhanced oral bioavailability in an extemporaneous liquid fixed-dose combination with isoniazid

Background: Coadministration of rifampicin (RIF)/isoniazid (INH) is clinically recommended to improve the treatment of tuberculosis. Under gastric conditions, RIF undergoes fast hydrolysis (a pathway hastened by INH) and oral bioavailability loss. Aim: We aimed to assess the chemical stabilization and the oral pharmacokinetics of RIF nanoencapsulated within poly(ε-caprolactone)-b-PEG-b-poly(ε-caprolactone) ‘flower-like’ polymeric micelles. Materials & methods: The chemical stability of RIF was evaluated in vitro under acid conditions with and without INH, and the oral pharmacokinetics of RIF-loaded micelles in rats was compared with those of a suspension coded by the US Pharmacopeia. Results: Nanoencapsulation decreased the degradation rate of RIF with respect to the free drug. Moreover, in vivo data showed a statistically significant increase of RIF oral bioavailability (up to 3.3-times) with respect to the free drug in the presence of INH. Conclusion: Overall results highlight the potential of this nanotechnology platform to develop an extemporaneous liquid RIF/INH fixed-dose combination suitable for pediatric administration.

Original submitted 6 April 2013; Revised submitted 7 August 2013

Electrosprayed core-shell polymer-lipid nanoparticles for active component delivery

A key challenge in the production of multicomponent nanoparticles for healthcare applications is obtaining reproducible monodisperse nanoparticles with the minimum number of preparation steps. This paper focus on the use of electrohydrodynamic (EHD) techniques to produce core-shell polymer-lipid structures with a narrow size distribution in a single step process. These nanoparticles are composed of a hydrophilic core for active component encapsulation and a lipid shell. It was found that core-shell nanoparticles with a tunable size range between 30 and 90 nm and a narrow size distribution could be reproducibly manufactured. The results indicate that the lipid component (stearic acid) stabilizes the nanoparticles against collapse and aggregation and improves entrapment of active components, in this case vanillin, ethylmaltol and maltol. The overall structure of the nanoparticles produced was examined by multiple methods, including transmission electron microscopy and differential scanning calorimetry, to confirm that they were of core-shell form.

Characteristics of polyurethane-based sustained release membranes for drug delivery

This paper is focused on the preparation and physicochemical characterization of two poly(ester ether urethane)s with rifampicin in their matrix and different molar concentrations of urethane groups. The polyurethanes with rifampicin were processed as asymmetrical microporous membranes by a phase inversion method and characterized by attenuated total reflection — Fourier transform infrared (ATR-FTIR) spectroscopy and differential scanning calorimetry (DSC). The influence of the surface morphology in the release of drug compounds was analyzed by scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle, and water uptake. The release of rifampicin depends on the molar concentration of urethane groups and also on the surface morphology of the polyurethane membranes. The antibacterial activity was evaluated with S. Epidermidis RP 62 A and P. Aeruginosa ATCC 1544. Finally, the biocompatibility of the polyurethane membranes was studied with human dermal fibroblasts (HDF) to evaluate the potential biomedical applications.

Preparation and characterization of imidacloprid lignin-polyethylene glycol matrices coated with ethylcellulose

Imidacloprid, a systemic insecticide that has a water solubility of 610 mg L(-1), has been formulated in lignin-polyethylene glycol matrices by a melting process. This formulation was coated in a Wurster type fluidized-bed equipment using ethylcellulose and dibutyl sebacate. Imidacloprid has been entrapped, with an entrapment efficiency higher than 87% in all cases. Thermogravimetric analysis, differential scanning calorimetry, and Fourier transformed infrared spectroscopy studies indicate the stability and compatibility of polymers and imidacloprid. Scanning electron microscopy images show a homogeneous film of ethylcellulose in coated formulations. From T(50) values (the time taken for 50% of the active ingredient to be released into water), the release rate of imidacloprid is controlled by changing the thickness of the coating film and modifying its surface properties by adding a plasticizer. T(50) values, ranging from 3.02 to 168.6 h, allow supplying the appropriate amount of imidacloprid in each specific agronomic practice to increase the efficiency of this bioactive material and minimize the risk of environmental pollution.

Formulation and optimization of sustained release Stavudine microspheres using response surface methodology

The aim of the current study was to formulate and optimize the formulation on the basis of in vitro performance of microsphere. A 3² full factorial design was employed to study the effect of independent variables, polymer-to-drug ratio (X₁) and stirring speed (X₂), on dependent variables, encapsulation efficiency, particle size, and time to 80% drug release. The best batch exhibited a high entrapment efficiency of 70% and mean particle size 290 μm. The drug release was also sustained for more than 12 hours. The study helped in finding the optimum formulation with excellent sustained drug release.

Rehydrated lyophilized rifampicin-loaded mPEG-DSPE formulations for nebulization

Rifampicin-loaded nanoparticles were prepared using two different molecular weights of poly-(ethylene oxide)-block-distearoyl phosphatidyl-ethanolamine (mPEG2000-DSPE and mPEG5000-DSPE) polymers. Particle sizes of all formulations studied were in the range of 162-395 nm. The entrapment efficiency (EE) was not affected by the copolymer's molecular weight, and the highest EE (100%) was obtained with drug to copolymer ratio of 1:5. The differential scanning calorimetry (DSC) thermograms showed Tg of rifampicin-loaded PEG-DSPE nanoparticles that shifted to a lower value, indicating entrapment of rifampicin in polymer matrix. The Fourier transformed infrared spectra revealed no chemical interactions between the drug and both copolymers. The in vitro drug release from the formulations occurred over 3 days and followed first-order release kinetic and Higuchi diffusion model. The nebulization of rehydrated lyophilized rifampicin mPEG-DSPE formulations had mass median aerodynamic diameter of 2.6 microm and fine particle fraction of 42%. The aerodynamic characteristic of the preparations was not influenced by the molecular weight of the copolymers. Therefore, it is suggested that both mPEG-DSPE are promising candidates as rifampicin carrier for pulmonary delivery.

Biowaiver monographs for immediate release solid oral dosage forms: rifampicin

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of new multisource and reformulated immediate release (IR) solid oral dosage forms containing rifampicin as the only Active Pharmaceutical Ingredient (API) are reviewed. Rifampicin's solubility and permeability, its therapeutic use and index, pharmacokinetics, excipient interactions and reported BE/bioavailability (BA) problems were taken into consideration. Solubility and absolute BA data indicate that rifampicin is a BCS Class II drug. Of special concern for biowaiving is that many reports of failure of IR solid oral dosage forms of rifampicin to meet BE have been published and the reasons for these failures are yet insufficiently understood. Moreover, no reports were identified in which in vitro dissolution was shown to be predictive of nonequivalence among products. Therefore, a biowaiver based approval of rifampicin containing IR solid oral dosage forms cannot be recommended for either new multisource drug products or for major scale-up and postapproval changes (variations) to existing drug products.

Use of ethylcellulose to control chlorsulfuron leaching in a calcareous soil

Controlled release formulations (CRFs) have been researched to reduce the water-polluting risk derived from the use of conventional formulations of chlorsulfuron. Coated chlorsulfuron granules were produced in a Wuster-type fluidized-bed equipment using two different amounts of ethylcellulose. The highest one was modified by the addition of a plasticizer such as dibutyl sebacate. The encapsulation efficiency and morphological properties of coated granules having been studied, the chlorsulfuron kinetic release in water was studied. In addition, the mobility of chlorsulfuron in a calcareous soil was finally carried out. High encapsulation efficiency was obtained, being nearly 100% in all cases. SEM pictures show a homogeneous film in coated CRFs; thickness oscillates between 23.32 microm for the system prepared with a 10% of ethylcellulose and 32.61 microm for the system prepared with a 20% ethylcellulose plus plasticizer. The rate of chlorsulfuron release from coated CRFs is diminished in all cases in relation to chlorsulfuron commercial formulation, the latter being completely dissolved in <1 h, but it took at least 50 days to release 90% of chlorsulfuron from the formulation coated with a 20% ethylcellulose plus plasticizer. Using a generic equation, the time taken for 50% of the active ingredient to be released into water (t(50)) was calculated. From the analysis of the t(50) values, it can be deduced that the release rate of chlorsulfuron can be mainly controlled by changing the thickness of the coating film, by modifying the surface properties of the coating film, and by adding a plasticizer. Mobility experiments carried out in calcareous soil show that the use of coated CRFs reduces the presence of chlorsulfuron in the leachate compared to commercial formulation.

Design and Study of Rifampicin Oral Controlled Release Formulations

Oral controlled release formulations of rifampicin have been developed by using hydroxypropyl methylcellulose polymer at different ratios. From in vitro release data, we found that the release was extended with an increase of polymer proportion from 20% to 40%. However, increase in polymer beyond 40% resulted in no significant change in the release rate. There was a distinct difference in the release rate and release character due to variation in the compression force. The release kinetics were analyzed using Ritger and Peppas exponential equation. Stability studies at ambient storage conditions for 1 year showed that formulations were stable.

Development andin-vitroevaluation of modified release tablets including ethylcellulose microspheres loaded with diltiazem hydrochloride

In this study, development of modified release tablet formulations containing diltiazem hydrochloride-loaded microspheres to be taken once rather than two or three times a day was attempted. For this purpose, ethylcellulose microspheres were prepared by emulsion-solvent evaporation technique. The influence of emulsifier type and drug/polymer ratio on production yield, encapsulation efficiency, particle size, surface morphology and in-vitro release characteristics of the microspheres was evaluated. Suitable microspheres were selected and tabletted using different tabletting agents, Ludipress, Cellactose80, Flow-Lac100 and excipients Compritol888 ATO, KollidonSR. Tablets were evaluated from the perspective of physical and in-vitro drug release characteristics. It was seen that type and ratio of the excipients played an important role in the tabletting of the microspheres. As a result, two tablet formulations containing 180 mg diltiazem hydrochloride and using either Compritol888 ATO or KollidonSR were designed successfully and maintained drug release for 24 h with zero order and Higuchi kinetics, respectively.

Tuberculosis chemotherapy: current drug delivery approaches

Tuberculosis is a leading killer of young adults worldwide and the global scourge of multi-drug resistant tuberculosis is reaching epidemic proportions. It is endemic in most developing countries and resurgent in developed and developing countries with high rates of human immunodeficiency virus infection. This article reviews the current situation in terms of drug delivery approaches for tuberculosis chemotherapy. A number of novel implant-, microparticulate-, and various other carrier-based drug delivery systems incorporating the principal anti-tuberculosis agents have been fabricated that either target the site of tuberculosis infection or reduce the dosing frequency with the aim of improving patient outcomes. These developments in drug delivery represent attractive options with significant merit, however, there is a requisite to manufacture an oral system, which directly addresses issues of unacceptable rifampicin bioavailability in fixed-dose combinations. This is fostered by the need to deliver medications to patients more efficiently and with fewer side effects, especially in developing countries. The fabrication of a polymeric once-daily oral multiparticulate fixed-dose combination of the principal anti-tuberculosis drugs, which attains segregated delivery of rifampicin and isoniazid for improved rifampicin bioavailability, could be a step in the right direction in addressing issues of treatment failure due to patient non-compliance.

Development of a simple method for the preparation of a silica gel based controlled delivery system with a high drug content

Silica gel was used as core particles to design a simple preparation for controlled delivery system with a high drug content. Drug loading was carried out by immersing the silica gel in a pre-heated drug solution or suspension. HPLC, SEM, DSC, PXRD analysis and N2 adsorption studies evaluated the drug-loading process. In the next step, the drug-loaded silica gel was coated with hydroxypropyl methylcellulose (HPMC) and an aqueous dispersion of ethylcellulose (Aquacoat) to control the drug release. The release profile was determined using a dissolution test. The results showed that silica gel could adsorb great quantities of the drug, up to about 450 mg/g, by repetition of the loading process. Evaluation of the drug-loading process indicates that drug deposition in the pores occurs during the loading process and the drug-loading efficacy is strongly related to the drug solubility. On the other hand, the dissolution test showed that the drug release could be controlled by polymer coating the drug-loaded silica gel. An HPMC undercoating effectively suppresses the drug release, as it smoothes the drug-loaded core surface and aids in the formation of a continuous Aquacoat coating film. The floating property was also observed during the dissolution test.

The influence of plasticizers on the release of theophylline from microporous-controlled tablets

The aim of present work was to investigate the influence of plasticizer on the release of theophylline from microporous-controlled tablets. Three plasticizers, acetyltributyl citrate (ATBC), castor oil, and triacetin, were included in this study. These plasticizers reduced the crystallinity of poly(epsilon-caprolactone) (PCL)/poly(ethylene glycol) (PEG)-blended films, and the most prominent change of enthalpy of fusion was the film plasticized by triacetin. This might be due to triacetin penetrating into both PCL and PEG domains. However, the lipophilic property of castor oil only allowed it to alter the crystallization of hydrophobic PCL domain. The Young's modulus and the tensile strength of films showed a decreased tendency while increasing the amount of plasticizer. The change of elongation of plasticized blended films was irregular and was dependent of the type of plasticizer. The size of micropores formed in the presence of plasticizer was larger than those micropores formed in its absence. The fatty plasticizer, castor oil, altered the thermal and mechanical performance and pore size of films via soluble in PCL domain, which resulted in the release of theophylline from castor oil plasticized-coated tablets, which in turn enhanced and closed to a constant release pattern.

Osmotically regulated asymmetric capsular systems for simultaneous sustained delivery of anti-tubercular drugs

Sustained release asymmetric membrane capsular systems were developed for simultaneous oral delivery of rifampicin and isoniazid sodium in order to reduce the problems associated with the multi drug therapy of tuberculosis. Dense semipermeable membrane coating capsules were also prepared for the delivery of these drugs by adopting two different filling approaches. In vitro release studies were carried out for both types of systems and the results were compared. Asymmetric membrane capsules provided sustained release of rifampicin associated with initial burst release, where isoniazid release rates were comparatively high due to higher aqueous solubility. Dense semipermeable membrane systems provided controlled release of both drugs but were devoid of initial burst release of isoniazid. To overcome these drawbacks, a modified asymmetric system was developed by adding appropriate amount of hydrophilic polymer mixture with isoniazid. The system provided satisfactory sustained release of rifampicin and isoniazid with initial burst release may be sufficient to achieve minimum effective concentration in blood. In vitro dissolution kinetics of the systems followed first order kinetics and statistical analysis of release rate data proved that modified asymmetric system was better amongst the developed systems.

Interaction of rifampicin and isoniazid with large unilamellar liposomes: spectroscopic location studies

The location of isoniazid and rifampicin, two tuberculostatics commonly used for the treatment of Mycobacterium tuberculosis and Mycobacterium avium complex infectious diseases, in bilayers of dimyristoyl-L-alpha-phosphatidylcholine (DMPC) and dimyristoyl-L-a-phosphatidylglycerol (DMPG) have been studied by 1H NMR and fluorimetric methods. Steady-state fluorescence intensity and fluorescence energy transfer studies between rifampicin and a set of functionalized probes [n-(9-anthroyloxy)stearic acids, n=2, 12] reveal that, in both systems, isoniazid is located at the membrane surface whereas rifampicin is deeply buried inside the lipid bilayers. Steady-state fluorescence anisotropy studies performed with the probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and trimethylammonium-diphenylhexa-triene (TMA-DPH), not only corroborate the above results, but also show that no changes in membrane fluidity were detected in either liposome. The 1H NMR results, in DMPC liposomes, confirm the location of rifampicin near the methylene group of the acyl chains of the lipid bilayers.