Preparation of novel cationic copolymer microspheres and evaluation of their function by in vitro and in vivo tests as pH-sensitive drug carrier systems

Novel pH-sensitive copolymer microspheres containing methylacrylic acid and styrene cross-linking with divinylbenzene were synthesized by free radical polymerization. The microspheres that were formed were then characterized by Fourier-Transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), size analysis, and X-ray analysis. The copolymer microspheres showed pulsatile swelling behavior whenthe pH of the media changed. The pH-sensitive microspheres were loaded with diltiazem hydrochloride (DH). The release characteristics of the free drug and the drug-loaded microspheres were studied under both simulated gastric conditions and intestinal pH conditions. The in vivo evaluation of the pulsatile preparation was subsequently carried out using beagle dogs as experimental subjects. The results demonstrated that the drug release exhibited a pulsatile character both in vitro and in vivo.     

Drug Product Development: A Technical Review of Chemistry,Manufacturing, and Controls Information for the Support of Pharmaceutical Compound Licensing Activities

Abstract

Tolmetin microspheres were prepared by the coacervation process from the ethylcellulose. Microspheres were obtained both in presence and without protecting colloids, such as polyisobutilene (PIB) or ethyl-vinylacetate copolimers (EVA). The effect of these agents on the preparation, drug content, wall thickness, surface morphology, drug dissolution arid release from microspheres, were evaluated. The dissolution rate analysis was carried out also in the presence of a surfactant (Tween 80) at different pH values.

In addition, microspheres containing Tolmetin as a core material were submitted to biological tests, in comparison with the free drug, to evaluate upon experimental models the antipyretic activity and the gastric tolerability.     

Evaluation of pH-Sensitivity and Drug Release Characteristics of (Polyacrylamide-Grafted-Xanthan)–Carboxymethyl Cellulose-Based pH-Sensitive Interpenetrating Network Hydrogel Beads

Novel pH-sensitive interpenetrating network hydrogel beads of polyacrylamide-grafted-xanthan (PAAm-g-XG) and sodium carboxymethyl cellulose (NaCMC) loaded with ketoprofen were prepared and evaluated for pH sensitivity and drug release characteristics. The pH-sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under the nitrogen atmosphere followed by alkaline hydrolysis. The grafting and alkaline hydrolysis reactions were confirmed by Fourier transform infrared spectroscopy. Differential scanning calorimetry and X-ray diffraction studies were carried out to know the crystalline nature of encapsulated drug. Scanning electron microscopic study revealed that the interpenetrating polymer network (IPN) beads possess porous matrix structure in alkaline pH whereas nonporous matrix structure was observed in acidic pH. The swelling of the beads and drug release was significantly increased when pH of the medium was changed from acidic to alkaline. The results of pulsatile swelling study indicated that the IPN beads changed their swelling behavior when pH of the external medium was altered. As pH of the medium was changed from 1.2 to 7.4, a considerable increase in swelling was observed for all the beads. However, swelling process was slower than the deswelling. At higher pH values, the carboxyl functional groups of hydrogels undergo ionization and the osmotic pressure inside the beads increases resulting in higher swelling. Drug release followed case II transport mechanism in acidic medium whereas anomalous/non-Fickian transport mechanism was observed in alkaline medium.     

In vitro evaluation of a novel pH sensitive drug delivery system based cockle shell-derived aragonite nanoparticles against osteosarcoma

ABSTRACT

Background: Osteosarcoma (OS) is a highly malignant primary bone cancer. Severe side effects and multidrug resistance are obstacles faced with chemotherapy against OS. With the hope to overcome the obstacles of the conventional chemotherapy, various targeted drug delivery systems using nanotechnology have been explored in the past few decades. Biogenic calcium carbonate (CaCO₃) has great potential to be a smart drug delivery system.

Results: In this study, cockle shells-derived aragonite nanoparticles (ANPs) were developed and loaded with doxorubicin (DOX). The physicochemical properties of the DOX-loaded ANPs (DOX-ANPs) were characterised by various techniques. The results of drug-loading study demonstrated that DOX was loaded onto ANPs at high loading and encapsulation efficiency (11.09% and 99.58%, respectively). The pH-sensitive release of DOX from DOX-ANPs was successful. At lower pH values (4.8), the release of DOX was much quicker than that at pH 7.4. Additionally, cellular uptake study using fluorescence microscopy showed obviously cellular uptake of DOX-ANPs through endocytosis. Moreover, the flow cytometric analysis revealed DOX-ANPs-induced cell cycle arrest, which was consistent with the mechanism of DOX. DOX-ANPs also showed an efficient cytotoxicity against OS cancer cells, close to the toxicity effect of free DOX at the same concentration. Morphological observations showed microvilli disappearance, chromatin condensation, cell shrinkage, membrane blebbing, and formation of apoptotic bodies, which confirmed both DOX-ANPs- and DOX-induced apoptosis of OS cancer cells in vitro.

Conclusion: Our findings indicated that ANPs could act as a pH-sensitive drug delivery against OS.     

In Vitro Evaluation of Albumin Microspheres Containing Actinomycin D

Abstract

Albumin microspheres containing actinomycin D were prepared by the heat stabilization method. The compata-bility of the drug with magnetite and the optimum stability of the drug in different pH were studied. Drug loaded albumin microspheres containing magnetite showed good magnetic response. Release of the drug was slow and continued for 7 days exhibiting sustained release property. The difference as regards to the size, shape, drug content and release rate from freshly prepared and freeze dried drug loaded albumin microspheres was negligible.     

A pH-sensitive nanocomposite microsphere based on chitosan and montmorillonite with in vitro reduction of the burst release effect

Objective: The aim of this study was to prepare pH-sensitive ofloxacin (OFL)/montmorillonite (MMT)/chitosan (CTS) nanocomposite microspheres that improve the burst release effect of the drug by the solution intercalation technique and emulsification cross-linking techniques. Methods: First, OFL/MMT hybrids were prepared through the solution intercalation technique. Then, OFL/MMT-intercalated OFL/MMT/CTS nanocomposite microspheres were obtained through emulsification cross-linking technology. The intercalated nanocomposite was confirmed by Fourier-transform infrared spectroscopy and X-ray diffraction. Finally, in vitro release of OFL from the microspheres was performed in simulated gastric fluids and simulated intestinal fluids. The effect of MMT content on drug encapsulation efficiency and the drug release of the nanocomposite microspheres were investigated. Results: The results showed that the release rate of OFL from the nanocomposite microspheres at pH 7.4 was higher than that at pH 1.2. Compared with pure CTS microspheres, the incorporation of certain amount of MMT in the nanocomposite microspheres can enhance the drug encapsulation efficiency and reduce the burst release. Conclusion: A sustained release particulate system can be obtained by incorporating MMT into the nanocomposite microspheres and can improve the burst release effect of the drug.     

In Vitro and In Vivo Performance of a Multiparticulate Pulsatile Drug Delivery System

ABSTRACT

The objective of this study was to investigate the in vitro and in vivo drug release performance of a rupturable multiparticulate pulsatile system, coated with aqueous polymer dispersion Aquacoat® ECD. Acetaminophen was used as a model drug, because in vivo performance can be monitored by measuring its concentration in saliva. Drug release was typical pulsatile, characterized by lag time, followed by fast drug release. Increasing the coating level of outer membrane lag time was clearly delayed. In vitro the lag time in 0.1 N HCl was longer, compared to phosphate buffer pH 7.4 because of ionisable ingredients present in the formulation (crosscarmelose sodium and sodium dodecyl sulphate). In vitro release was also longer in medium with higher ion concentration (0.9% NaCl solution compared to purified water); but independent of paddle rotation speed (50 vs.100 rpm). Macroscopically observation of the pellets during release experiment confirms that the rupturing of outer membrane was the main trigger for the onset of release. At the end of release outer membrane of all pellets was destructed and the content completely released.

However, pellets with higher coating level and correspondingly longer lag time showed decreased bioavailability of acetaminophen. This phenomenon was described previously and explained by decreased liquid flow in the lower part of intestine. This disadvantage can be considered as a limitation for drugs (like acetaminophen) with high dose and moderate solubility; however, it should not diminish performance of the investigated system in principle.     

Evaluation of pH-sensitivity and drug release characteristics of (polyacrylamide-grafted-xanthan)-carboxymethyl cellulose-based pH-sensitive interpenetrating network hydrogel beads

Novel pH-sensitive interpenetrating network hydrogel beads of polyacrylamide-grafted-xanthan (PAAm-g-XG) and sodium carboxymethyl cellulose (NaCMC) loaded with ketoprofen were prepared and evaluated for pH sensitivity and drug release characteristics. The pH-sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under the nitrogen atmosphere followed by alkaline hydrolysis. The grafting and alkaline hydrolysis reactions were confirmed by Fourier transform infrared spectroscopy. Differential scanning calorimetry and X-ray diffraction studies were carried out to know the crystalline nature of encapsulated drug. Scanning electron microscopic study revealed that the interpenetrating polymer network (IPN) beads possess porous matrix structure in alkaline pH whereas nonporous matrix structure was observed in acidic pH. The swelling of the beads and drug release was significantly increased when pH of the medium was changed from acidic to alkaline. The results of pulsatile swelling study indicated that the IPN beads changed their swelling behavior when pH of the external medium was altered. As pH of the medium was changed from 1.2 to 7.4, a considerable increase in swelling was observed for all the beads. However, swelling process was slower than the deswelling. At higher pH values, the carboxyl functional groups of hydrogels undergo ionization and the osmotic pressure inside the beads increases resulting in higher swelling. Drug release followed case II transport mechanism in acidic medium whereas anomalous/non-Fickian transport mechanism was observed in alkaline medium.     

Moment Analysis for the Evaluation of In Vitro Drug Release and In Vivo Bioavailability of Theophylline Microcapsules

Abstract

Statistical moment analysis has been used to establish an in vitro-in vivo correlation for five types of theophylline ethylcellulose microcapsules prepared by using various concentrations of ethylene-vinyl acetate (EVA) copolymer as a coacervation-inducing agent. The concentration of EVA copolymer was found to be played an important function in the controlled release of theophylline microcapsules. Correlations were found between the in vitro dissolution behavior, e.g., MDT _0→7, in vitro' and the rate of bioavailability, e.g., Cmax, Tmax, MDT _{in vivo} or MRT_0→2, although there was no valid correlation with the extent of bioavailability, e.g., AUC_0→27. Thus, moment analysis by studying the quantitative in vitro-in vivo correlations relating to drug release was validated.     

In Vitro and In Vivo Preparation Evaluations of Bleomycin Implants and Microspheres Prepared with DL-Poly (Lactide-Co-Glycolide)

ABSTRACT

In this investigation, poly(lactide-co-glycolide) (PLGA) gel implants and microspheric depot systems of bleomycin (BLM) were formulated and evaluated in vivo in mice bearing transplantable solid tumor (fibrosarcoma). The pharmacodynamic studies showed that both the formulations retarded tumor growth significantly (p < 0.05) when compared to the control animals (without any drug treatment). Preliminary pharmacokinetic studies illustrated controlled release of the drug into the systemic circulation to elicit the anti-neoplastic action. The gel implants showed better release characteristics and greater pharmacodynamic action when compared to the microspheres, thus demonstrating the feasibility of employing biodegradable depot polymer gel matrix for chronic cancer therapy.     

In Vivo Characteristics of Injectable Poly(DL-Lactic Acid) Microspheres for Long-Acting Drug Delivery

Abstract

Poly(DL-lactic acid) (PLA) microspheres containing testosterone (T) were prepared by the solvent evaporation process to evaluate their physical properties such as size distribution, shape, drug content, in vivo controlled drug release, pharmacological influences on the prostate gland in castrated rats, and histopathological findings of tissues surrounding the implants. The in vivo release of T from PLA microspheres containing 30 mg of drug obtained with chloroform was continued over a 6-week period. This effect is attributed to high dispersibility ofT in the device when obtained with chloroform. Both serum drug levels and prostate gland weight recovery suggested the effects of a long-acting drug delivery system. The histopathological findings showed that the devices used were completely degraded 10 weeks after injection.     

Comparative In Vitro evaluation of cumulative release of the urinary antiseptics Nalidixic acid,Pipemidic acid,Cinoxacin, and norfloxacin from white beeswax Microspheres

Abstract

The in vitro diffusion of nalidixic acid (1), pipemidic acid (2), cinoxacin (3), and norfloxacin (4) was studied. The transfer rate constants (k_d) from simulated gastro-intestinal juices to simulated plasma, throughout artificial wall lipid membranes, were defined. The k_d values suggested that the four drugs are absorbed both in gastric and intestinal environments in similar amounts. To obtain lack of gastric unwanted effects white beeswax microspheres containing 1, 2, 3, and 4 were investigated as a vehicle for the drug intestinal release; they were prepared by the meltable dispersion process using wetting agents. Discrete, reproducible free flowing microspheres were obtained. The drug content increased when the particle size growed; it ranged from 4% to 18%. More than 95% of the isolated microspheres were of particle size range 100–500 μm. The drug release was evaluated in vitro. Dissolution of entrapped active ingredients was greatly retarded allowing absorption only in the intestinal tract as result of microsphere formation.     

In Vitro and In Vivo Release of Naltrexone from Biodegradable Depot Systems

ABSTRACT

The aim of this study was to prepare poly(d, l-lactide) (PLA) microspheres containing naltrexone (NTX) by a solvent evaporation method, and to evaluate both in vitro and in vivo release characteristics and histopathological findings of tissue surrounding an implant formulation in rats.

This method enabled the preparation of microspheres of regular shape and relatively narrow particle size distribution. The in vitro release profiles of NTX from PLA microspheres showed the release of NTX did not follow zero-order kinetics. An initial burst release was observed, subsequently followed by a nearly constant rate of 0.4% per day after ten days. The cumulative amount of NTX released at the end of 60 days was 80%. Compressed microspheres showed near zero-order sustained release of NTX for 360 days. The plasma NTX levels in rats showed that for compressed microspheres NTX concentrations were constant and exceeded 2 ng/mL for 28 days. Throughout the 28 days of study, the implantations cause a minor inflammatory response, which can be regarded as a normal defence mechanism. The sustained release performance of NTX from the biodegradable depot systems may provide a reliable, convenient, and safe mechanism for the administration of NTX for the long-term treatment of opioid dependence.     

Acrylic acid–methyl methacrylate copolymer for oral prolonged drug release

Acrylic acid (AA)–methyl methacrylate (MMA) based copolymers, in different molar ratios (3:7, 4:6, 5:5, 6:4, and 7:3) were synthesized using tetrahydrofuran as solvent and AIBN as free radical initiator. Increase in acrylic acid concentration promoted pH-dependent swelling of copolymer and copolymer AA:MMA (3:7) was selected due to minimum swelling. ATR/FTIR and ¹H NMR spectra of the copolymer showed absence of vinyl bond/protons present in the monomers suggesting successful polymerization. The copolymer was hemocompatible. Flurbiprofen sodium microspheres made with the copolymer, by oil/oil solvent evaporation, were spherical, anionic (zeta potential −59.0 mV) and contained 4.53% drug. ATR spectrum of microspheres showed peaks for aromatic C=C stretching and substituted benzene ring, indicating entrapment of flurbiprofen. XRD analysis revealed crystalline structure of flurbiprofen while copolymer and microspheres were amorphous. DSC thermograms showed a sharp melting endotherm of flurbiprofen sodium at 129.26°C against broad endotherms of copolymer and microspheres having peaks at 82.24 and 86.59°C, respectively. The thermogram of microspheres did not show the melting peak of flurbiprofen. The microspheres exhibited no drug release at pH <6.8 and released 83.4 and 99% drug at pH 6.8 and 7.4 in 3 h. The microspheres did not adhere on gastric mucosa at pH 1.2 but showed mucoadhesion time of 28 min on intestinal mucosa at pH 6.8. Thus, the microspheres on oral administration, would release the drug in distal ileum, suggesting the potential of the hemocompatible copolymer for enteric coating for prolonged drug release.     

Carnauba Wax Microspheres Loaded with Valproic Acid: Preparation and Evaluation of Drug Release

Abstract

To minimize unwanted toxic effects of valproic acid (1) by the kinetic control of drug release, gastroresistant carnauba wax microspheres loaded with the antiepileptic agent were prepared. The preparation was based on a technique involving melting and dispersion of drug-containing wax in an aqueous medium. The resulting emulsion after cooling under rapid stirring produced solid, discrete, reproducible free flowing microspheres which converted the liquid drug droplets into solid material. About 94% of the isolated microspheres were of particle size range 200-425 μm. The microspheres were analyzed to determine the drug content in various particle size range and to characterize the in vitro release profile. The average drug content was 26% w/w. The intestinal drug discharge of 1 from the carnauba wax microspheres was studied and compared with the release patterns observed for white beeswax and hexadecanol microspheres previously described. The drug release performance was greatly affected by the material used in the microencapsulation process. In the intestinal environment carnauba wax microspheres exhibited more rapid initial rate of release and about 80% of the entrapped drug was discharged in 120 min while complete release occurred in about 8 h.     

Peroral Sustained-Release Film-Coated Pellets as a Means to Overcome Physicochemical and Biological Drug-Related Problems. I. In Vitro Development and Evaluation

Abstract

In vitro preformulation testing has shown that the solubility and dissolution rate of the model drug compound ucb 11056 are highly pH dependent. Considering this, different sustained-release (SR) oral dosage forms of ucb 11056 were developed aiming to obtain the most constant and complete release of the drug during transit in the gastrointestinal (GI) tract. Classical approaches based on the use of SR formulations such as hydrophilic matrix tablets or pellets coated with one film-forming polymer (Eudragit NE30D or L30D-55) did not fulfill all expectations on the basis of their in vitro evaluation, i.e., the drug release and pattern remained highly dependent on the pH of the dissolution medium. Therefore, taking advantage of the flexibility of release adjustment obtainable from coating of pellets with different kinds of pH-sensitive film layers, a quite satisfactory pH independence of the release characteristics was obtained using formulation blends of neutral and anionic acrylic polymers. For the selected SR pellets batch 15 coated with NE30D/L30D-55 (7:3), the tridimensional topographic representation of the drug release versus time and pH showed that, notwithstanding the pH-dependent aqueous solubility of the drug, the release profiles were relatively homogeneous for any pH value ranging between 1 and 7.     

Preparation,Characterization and In-Vitro Release Kinetics of Salbutamol Sulphate Loaded Albumin Microspheres

Abstract

Salbutamol sulphate loaded Bovine serum albumin microspheres were prepared by heat denaturation method. The effects of such preparation conditions as denaturation temperature, denaturation time, protein concentration and phase volume ratio on the extent of drug loading, size and size distribution and drug release were studied. An increase in protein concentration from 5% w/v to 15% w/v increased the mean particle size from 8.5 μm to 16.6 μm and decreased the drug loading from 46% w/w to 18% w/w. A decrease in the phase volume ratio substantially lowered mean particle size and size distribution. An increase in the severity of denaturaion conditions lowered both the drug incorporated and drug released. The kinetics of drug release from microspheres were compared to the theoretical models of Higuchi diffusional release and first order release. Both the models gave an adequate fit to the data. Scanning electron microscopy revealed that the dummy microspheres are spherical with smooth surfaces. As the drug-protein ratio increased, the microspheres exhibited rough surfaces showing the presence of drug crystals.     

Dissolution Characteristics of Polycaprolactone-Polylactide Microspheres of Chlorpromazine

Abstract

Studies were conducted on the preparation of controlled release polycaprolactone-polylactide microcapsules of chlorpromazine and on release of the drug from the microcapsules in pH 7.0 buffer medium. A wide range of release rates of the drug was obtained by simple change in the polymer system. Chlorpromazine was released from the microspheres in a biphasic manner consisting of an initial fast release phase followed by a slow-release phase. Increasing the drug content increased the initial drug release rate but no significant drug loading effect on the second stage dissolution rate was noted. There was no significant effect of particle size on the drug release rate from the microspheres. The swelling property of the microspheres and the agglomerate nature of the sieve fractions may complicate the drug release kinetics and obscure the particle size effect on dissolution rate.     

Acrylic acid–methyl methacrylate (2.5:7.5/2:8) enteric copolymer for colon targeted drug delivery

Enteric copolymers of acrylic acid and methyl methacrylate (2.5:7.5 and 2:8) were prepared using tetrahydrofuran as solvent and AIBN as free radical initiator for colon targeting. FTIR and ¹H NMR spectra of the copolymers showed absence of vinyl bond/protons present in the monomers suggesting successful polymerization. Flurbiprofen sodium microspheres (M1 and M2) made with the copolymers, by oil/oil solvent evaporation, were spherical, anionic (zeta potential –57.8 and –53.7 mV) and contained 5.47 and 5.89% drug. FTIR spectrum of microspheres showed peaks for aromatic C = C stretching and substituted benzene ring, indicating entrapment of flurbiprofen. PXRD revealed crystalline structure of flurbiprofen while copolymer and microspheres were amorphous. DSC thermograms showed a sharp melting endotherm of flurbiprofen sodium at 129.26°C against broad endotherms of copolymers and microspheres. The microspheres released 43 and 36% drug at pH 6.8 in 2 h and 99 and 96% at pH 7.4 in next 3–4 h.The microspheres did not adhere on gastric-mucosa at pH 1.2 but showed mucoadhesion time of 18 min and 9 min on intestinal mucosa at pH 6.8. Thus, the microspheres on oral administration, would release the drug in colon, suggesting the potential of the hemocompatible copolymers for pH dependent colon targeted drug delivery system.     

Preparation of grafted microspheres CPVA-g-PSSS and studies on their drug-carrying and colon-specific drug delivery properties

Sodium 4-styrene sulfonate (SSS) was graft-polymerized on the surfaces of crosslinked polyvinyl alcohol (CPVA) microspheres in a manner of surface-initiated graft-polymerization by using cerium salt-hydroxyl group redox initiation system, obtaining the grafted microspheres CPVA-g-PSSS. The chemical structure and physicochemical characters of CPVA-g-PSSS microspheres were fully characterized with infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and zeta potential determination. The aim of this work is to constitute a novel colon-specific drug delivery system via molecular design by using CPVA-g-PSSS microspheres as the drug-carrying material and by taking metronidazole (MTZ) as the model drug. The drug-carrying ability and mechanism of the grafted microspheres CPVA-g-PSSS for MTZ were investigated. Finally, in-vitro release tests for the drug-carrying microspheres were conducted. The experimental results show that in an acidic medium, the grafted microspheres CPVA-g-PSSS exhibit strong adsorption ability for MTZ by driving of electrostatic interaction, and have an adsorption capacity of 112 mg/g, displaying the high efficiency of drug-carrying. The in-vitro release behavior of the drug-carried microspheres is highly pH-sensitive. In the medium of pH = 1, the drug-carrying microspheres do not release the drug, whereas in the medium of pH = 7.4, a sudden delivery phenomenon of the drug will occur, displaying an excellent colon-specific drug delivery behavior.