Factors influencing the profiles of TRH release from copoly(d,l-lactic/glycolic acid) microspheres

Peptide loaded polymeric nanoparticles by non-aqueous nanoprecipitation

It is always a challenge to encapsulate water-soluble peptides in polymer nanoparticle (NP) systems. We establish and validate our newly developed non-aqueous nanoprecipitation method to encapsulate neuro-peptides drugs such as oxytocin and Luteinizing hormone-releasing hormone (LHRH) in poly(sebacic anhydride) (PSA) NPs. NPs were prepared by a solvent-antisolvent process under a strict anhydrous environment to obtain high drug loading and to avoid premature PSA degradation and drug release. Dynamic light scattering (DLS) and Scanning Electron Microscopy (SEM) reveal the size for both drug loaded PSA NPs to ∼ 300 nm. The drug loaded NPs were dispersible and spherical in shape with uniform morphology. The in vitro release profile of oxytocin from PSA NPs occurs with the burst release of ∼ 50% within the first hour in the aqueous release medium, whereas LHRH release is comparatively slow. Thus, looking into the fast degrading properties of PSA and drug release behavior, the developed NPs can be used for direct delivery of the neuropeptides to the olfactory epithelium using a refillable nasal atomizer that deposits mist onto the olfactory neuro-epithelium. We also applied our developed method to prepare NPs of poly(lactic-co-glycolic acid) (PLGA), polylactic acid (PLA), and poly(ε-caprolactone) (PCL). A Thyrotropin releasing hormone (TRH) was used as the sample neuropeptide drug to validate our non-aqueous method. The results reveal the formation of TRH loaded PLGA, PLA and PCL NPs with 100% drug loading. TEM analysis shows the formation of spherical NPs, having similar release properties as those of PSA NPs. Overall, we report that our developed method is suitable for co-encapsulating hydrophilic drugs in polymer NPs with high drug loading and release properties.

Coupling the in vivo performance to the in vitro characterization of PLGA microparticles

The main objective of the study was to determine if rodent housing conditions, specifically housing climate, could impact the in vivo performance of poly(lactide-co-glycolide) (PLGA) microspheres through temperature modification of the subcutaneous space. Vivitrol®, a once monthly naltrexone injectable suspension, was chosen as a model PLGA microparticle formulation for this study. Two lots of Vivitrol were used to ascertain any potential differences that may exist between the batches and if in vitro characterization techniques could delineate any variation(s). The pharmacokinetics of the naltrexone-PLGA microparticles were determined in the rodent model under two different housing climates (20 vs. 25 °C). The results demonstrate that such difference in housing temperature resulted in a change in subcutaneous temperature but actually within a narrow range (36.31-36.77 °C) and thus minimally influenced the in vivo performance of subcutaneously injected microparticles. The shake-flask method was used to characterize the in vitro release at 35, 36, and 37 °C and demonstrated significant differences in the in vitro release profiles across this range of temperatures. Minimal differences in the in vitro characterization of the two lots were found. While these results did not provide statistical significance, the local in vivo temperature may be a parameter that should be considered when evaluating microparticle performance. The IVIVCs demonstrate that in vitro release at 37 °C may not accurately represent the in vivo conditions (i.e., subcutaneous space in rodents), and in certain instances lower in vitro release temperatures may more accurately represent the in vivo microenvironment and provide better correlations. Future studies will determine the extent temperature and specifically co-housing, may have on the relative impact of the in vivo performance of injectable polymeric microparticles based upon the significant differences observed in the in vitro release profiles across the range of 35-37 °C.

How subtle differences in polymer molecular weight affect doxorubicin-loaded PLGA nanoparticles degradation and drug release

Aims: To evaluate the influence of minor differences in molecular weights of commercially available low molecular weight PLGA grades on the kinetics of doxorubicin release from the nanoparticles.Methods: Three low-molecular weight 50/50 PLGA polymers were thoroughly characterised concerning intrinsic viscosity, molecular weight (Mw), acid value, and residual monomer content. The doxorubicin-loaded nanoparticles prepared using these polymers were evaluated concerning the kinetics of drug release and hydrolytic degradation.Results: The Mw of the polymers were slightly different: 10.2, 10.3, and 4.7 kDa. The nanoparticles obtained from the polymer with Mw of 4.7 kDa exhibited considerably higher rates of drug release and polymer degradation.Conclusion: In the case of low molecular weight PLGA grades even a few kilodaltons could be important for the batch-to-batch reproducibility of the nanoformulation parameters. These results bring forward the importance of in-house characterisation of the polymers to be used for the nanoparticle preparation.

Carriers for the tunable release of therapeutics: etymological classification and examples

Introduction Physiological processes at the molecular level take place at precise spatiotemporal scales, which vary from tissue to tissue and from one patient to another, implying the need for carriers that enable tunable release of therapeutics. Areas covered Classification of all drug release to intrinsic and extrinsic is proposed, followed by the etymological clarification of the term 'tunable' and its distinction from the term 'tailorable'. Tunability is defined as analogous to tuning a guitar string or a radio receiver to the right frequency using a single knob. It implies changing a structural parameter along a continuous quantitative scale and correlating it numerically with the release kinetics. Examples of tunable, tailorable and environmentally responsive carriers are given, along with the parameters used to achieve these levels of control. Expert opinion Interdependence of multiple variables defining the carrier microstructure obstructs the attempts to elucidate parameters that allow for the independent tuning of release kinetics. Learning from the tunability of nanostructured materials and superstructured metamaterials can be a fruitful source of inspiration in the quest for the new generation of tunable release carriers. The greater intersection of traditional materials sciences and pharmacokinetic perspectives could foster the development of more sophisticated mechanisms for tunable release.

Polymeric nanoparticles and microparticles for the delivery of peptides, biologics, and soluble therapeutics

Biologically derived therapeutics, or biologics, are the most rapidly growing segment of the pharmaceutical marketplace. However, there are still unmet needs in improving the delivery of biologics. Injectable polymeric nanoparticles and microparticles capable of releasing proteins and peptides over time periods as long as weeks or months have been a major focus in the effort to decrease the frequency of administration. These particle systems fit broadly into two categories: those composed of hydrophilic and those composed of hydrophobic polymeric scaffolds. Here we review the factors that contribute to the slow and controlled release from each class of particle, as well as the effects of synthesis parameters and product design on the loading, encapsulation efficiency, biologic integrity, and release profile. Generally, hydrophilic scaffolds are ideal for large proteins while hydrophobic scaffolds are more appropriate for smaller biologics without secondary structure. Here we also introduce a Flash NanoPrecipitation method that has been adopted for encapsulating biologics in nanoparticles (40-200nm) at high loadings (50-75wt.%) and high encapsulation efficiencies. The hydrophilic gel interior and hydrophobic shell provide an opportunity to combine the best of both classes of injectable polymeric depots.

IVIVC from Long Acting Olanzapine Microspheres

In this study, four PLGA microsphere formulations of Olanzapine were characterized on the basis of their in vitro behavior at 37°C, using a dialysis based method, with the goal of obtaining an IVIVC. In vivo profiles were determined by deconvolution (Nelson-Wagner method) and using fractional AUC. The in vitro and in vivo release profiles exhibited the same rank order of drug release. Further, in vivo profiles obtained with both approaches were nearly superimposable, suggesting that fractional AUC could be used as an alternative to the Nelson-Wagner method. A comparison of drug release profiles for the four formulations revealed that the in vitro profile lagged slightly behind in vivo release, but the results were not statistically significant (P < 0.0001). Using the four formulations that exhibited different release rates, a Level A IVIVC was established using the deconvolution and fractional AUC approaches. A nearly 1 : 1 correlation (R² > 0.96) between in vitro release and in vivo measurements confirmed the excellent relationship between in vitro drug release and the amount of drug absorbed in vivo. The results of this study suggest that proper selection of an in vitro method will greatly aid in establishing a Level A IVIVC for long acting injectables.

PLGA/Ag nanocomposites: in vitro degradation study and silver ion release

New nanocomposite films based on a biodegradable poly (DL-Lactide-co-Glycolide) copolymer (PLGA) and different concentration of silver nanoparticles (Ag) were developed by solvent casting. In vitro degradation studies of PLGA/Ag nanocomposites were conducted under physiological conditions, over a 5 week period, and compared to the behaviour of the neat polymer. Furthermore the silver ions (Ag(+)) release upon degradation was monitored to obtain information on the properties of the nanocomposites during the incubation. The obtained results suggest that the PLGA film morphology can be modified introducing a small percentage of silver nanoparticles that do not affect the degradation mechanism of PLGA polymer in the nanocomposite. However results clearly evinced the stabilizing effect of the Ag nanoparticles in the PLGA polymer and the mineralization process induced by the combined effect of silver and nanocomposite surface topography. The Ag(+) release can be controlled by the polymer degradation processes, evidencing a prolonged antibacterial effect.

Microparticulate based topical delivery system of clobetasol propionate

Psoriasis is a chronic, autoimmune skin disease affecting approximately 2% of the world's population. Clobetasol propionate which is a superpotent topical corticosteroid is widely used for topical treatment of psoriasis. Conventional dosage forms like creams and ointments are commonly prefered for the therapy. The purpose of this study was to develop a new topical delivery system in order to provide the prolonged release of clobetasol propionate and to reduce systemic absorption and side effects of the drug. Clobetasol propionate loaded-poly(D,L-lactic-co-glycolic acid) (PLGA) microspheres were prepared by oil-in-water emulsion-solvent evaporation technique. Particle size analysis, morphological characterization, DSC and XRD analyses and in vitro drug release studies were performed on the microparticle formulations. Emulgel formulations were prepared as an alternative for topical delivery of clobetasol propionate. In vitro drug release studies were carried out from the emulgel formulations containing pure drug and drug-loaded microspheres. In addition, the same studies were performed to determine the drug release from the commercial cream product of clobetasol propionate. The release of clobetasol propionate from the emulgel formulations was significantly higher than the commercial product. In addition, the encapsulation of clobetasol propionate in the PLGA microspheres significantly delayed the drug release from the emulgel formulation. As a result, the decrease in the side effects of clobetasol propionate by the formulation containing PLGA microspheres is expected.

Preparation of ONO-1301-loaded poly(lactide-co-glycolide) microspheres and their effect on nerve conduction velocity

Objectives

The aim of this study was to prepare poly(lactide-co-glycolide) (PLGA) microspheres containing ONO-1301, a novel long-acting prostacyclin agonist with thromboxane synthase inhibitory activity, with 10% of drug released in the initial burst and a sustained-release period of about 3 weeks after administration. The effect of PLGA type (molecular weight and the lactide/glycolide (L/G) ratio in PLGA), the preparative conditions and the particle size on the in-vitro release profile were examined. The effect of optimized ONO-1301-loaded PLGA microspheres on delayed nerve condition velocity (NCV) was investigated in streptozotocin (STZ) induced diabetic rats.

Methods

ONO-1301 PLGA microspheres were produced by the oil-in-water emulsion/solvent evaporation method. Drug release from the prepared microspheres was monitored in phosphate buffer solution at 37°C for 4 weeks by high-performance liquid chromatography. The in-vivo study was performed in STZ-induced diabetic rats treated with optimized ONO-1301 PLGA microspheres (10 mg/kg by intramuscular or subcutaneous injection every 3 weeks). NCV was measured in the thigh 4, 8 and 12 weeks after induction.

Key findings

The molecular weights of PLGA, the L/G ratio in PLGA and the particle diameter all affected the length of the sustained release period. Drug release from microspheres containing PLGA 5050 (MW 50 000, L/G 50/50), with an average diameter of about 30 µm, could be sustained for 3 weeks in vitro. In the in-vivo study, delayed NCV was significantly increased by treatment with these ONO-1301 PLGA microspheres once every 3 weeks, in comparison with vehicle only.

Conclusion

Local intramuscular injection of sustained-release ONO-1301 PLGA microspheres improved delayed NCV in STZ-induced diabetic rats.

Automatic, sequential power generation for prolonging the net lifetime of a miniature biofuel cell stack

A sequential power generation system for prolonging the net lifetime of a miniature biofuel cell stack has been developed. The system consists of layered chambers of enzyme fuel cells designed to be exposed sequentially to fuel solution by automatically switched fuel flow. The cell chambers were initially separated by magnetized plastic covers sealed with a degradable glue, poly(lactic-co-glycolic acid) (PLGA). The time that the cover was opened by attraction with an external magnet, thereby activating the following cell, was adjustable from a few hours to a few weeks by controlling the weight ratio of Fe(3)O(4) in the covers and the molecular weight of PLGA. By using sequential power generation in this way, the power output of the system was stable for longer periods, and therefore the net lifetime of the stack has been extended as compared with that of a single biofuel cell.

Glycyrrhetic acid-loaded microparticles: liver-specific delivery and therapeutic potential against carbon tetrachloride-induced hepatitis

The microparticles (MPs) of an anti-hepatotoxic drug, glycyrrhetic acid (GLA), were prepared using poly(dl-lactic acid-co-glycolic acid) as a drug carrier, and their in-vitro properties, biodistribution and therapeutic effects were investigated. The MPs showed a particle diameter distribution of 1.0–1.4 μm and a drug content of approximately 10% (w/w). In the in-vitro release in a mixture of methanol and phosphate-buffered saline pH 7.4 (3:7, v/v), slow release was observed after an initial burst release of approximately 30% (w/w). After i.v. administration of MPs in normal mice, GLA was mainly distributed to the liver. After i.v. administration in normal mice, the MPs maintained a much higher liver concentration than did GLA solution, and the plasma concentration also tended to be higher for MPs than for GLA solution. As to therapeutic effect, the liver was damaged by repeated injection of carbon tetrachloride (CCl4) in mice every 48 h, and the drugs were administered intravenously as a single dose 3 h after the first injection of CCl4. At 10 mg GLA eq. kg−1, the MPs significantly suppressed the plasma level of glutamic pyruvic transaminase for at least 141 h after administration, while GLA solution did not become significantly effective within 45 h post-administration. MPs are suggested as a possible useful system to prolong the therapeutic effect of GLA.

Formulation and performance characterization of radio-sterilized "progestin-only" microparticles intended for contraception

The aim of this study was to formulate and characterize a microparticulate system of progestin-only contraceptive. Another objective was to evaluate the effect of gamma radio-sterilization on in vitro and in vivo drug release characteristics. Levonorgestrel (LNG) microspheres were fabricated using poly(lactide-co-glycolide) (PLGA) by a novel solvent evaporation technique. The formulation was optimized for drug/polymer ratio, emulsifier concentration, and process variables like speed of agitation and evaporation method. The drug to polymer ratio of 1:5 gave the optimum encapsulation efficiency. Speed of agitation influenced the spherical shape of the microparticles, lower speeds yielding less spherical particles. The speed did not have a significant influence on the drug payloads. A combination of stabilizers viz. methyl cellulose and poly vinyl alcohol with in-water solvent evaporation technique yielded microparticles without any free drug crystals on the surface. This aspect significantly eliminated the in vitro dissolution "burst effect". The residual solvent content was well within the regulatory limits. The microparticles passed the test for sterility and absence of pyrogens. In vitro dissolution conducted on the product before and after gamma radiation sterilization at 2.5 Mrad indicated no significant difference in the drug release patterns. The drug release followed zero-order kinetics in both static and agitation conditions of dissolution testing. The in vivo studies conducted in rabbits exhibited LNG release up to 1 month duration with drug levels maintained within the effective therapeutic window.

Fabrication, characterization and in vivo studies of biodegradable gamma sterilized injectable microparticles for contraception

A Levonorgestrel-loaded microparticulate system was developed with gelatin and bovine serum albumin using triple emulsion technique coupled with chemical cross-linking thermal rigidization method. The formulation was optimized for various formulation variables and process parameters. The microparticulate system was characterized by scanning electron microscopy, encapsulation efficiency, moisture content, IR, DSC, XRD, residual solvent content and evaluated for sterility, abnormal toxicity and absence of pyrogens. Microparticles were sterilized by gamma irradiation at 2.5 Mrad. The system was injected intramuscularly in rabbits and drug blood levels estimated using radioimmunoassay technique. An optimized drug to polymer ratio of 0.4:0.75 w/w gave drug encapsulation efficiency of about 40%. The in vitro drug release followed Higuchi square root kinetics. In in vivo studies the AUC0-t was found to be 12849.25 pg/mL.day(-1) with mean residence time calculated to be about 16 days and Kel of 0.02 day(-1). Levonorgestrel (LNG) levels were maintained between 200 and 400 pg/mL. The pharmacokinetic results indicate that LNG is released from the injectable microparticles for a period of one-month duration.

Poly(ethylene glycol)-modified proteins: implications for poly(lactide-co-glycolide)-based microsphere delivery

The reduced injection frequency and more nearly constant serum concentrations afforded by sustained release devices have been exploited for the chronic delivery of several therapeutic peptides via poly(lactide-co-glycolide) (PLG) microspheres. The clinical success of these formulations has motivated the exploration of similar depot systems for chronic protein delivery; however, this application has not been fully realized in practice. Problems with the delivery of unmodified proteins in PLG depot systems include high initial "burst" release and irreversible adsorption of protein to the biodegradable polymer. Further, protein activity may be lost due to the damaging effects of protein-interface and protein-surface interactions that occur during both microsphere formation and release. Several techniques are discussed in this review that may improve the performance of PLG depot delivery systems for proteins. One promising approach is the covalent attachment of poly(ethylene glycol) (PEG) to the protein prior to encapsulation in the PLG microspheres. The combination of the extended circulation time of PEGylated proteins and the shielding and potential stabilizing effects of the attached PEG may lead to improved release kinetics from PLG microsphere system and more complete release of the active conjugate.

Impact of bulk and surface properties of some biocompatible hydrophobic polymers on the stability of methylene chloride-in-water mini-emulsions used to prepare nanoparticles by emulsification–solvent evaporation

The emulsifying and stabilizing ability of several hydrophobic (insoluble in water and soluble in volatile organic solvents) polymers, such as Eudragit RL, Eudragit RS, PLGA, PCL, and their mixtures, with regard to the methylene chloride (MC)-in-water mini-emulsions, has been compared to the viscosity of MC solutions and to the properties of adsorption and spread monolayers of these polymers. Eudragits RS and RL contain approximately 2.5 and approximately 5 mol% of pendent cationic trimethylammonium (TMA) groups per approximately 164 g/mol segments, whereas PLGA and PCL contain 1 and 2 polar carbonyl groups per 130 and 114 g/mol, respectively. The electrostatic attraction between the dipoles, formed by TMA groups and the condensed counter ions in the MC solutions, leads to the contraction of macromolecular coils of Eudragits, whereas the PLGA and PCL macromolecules, interacting by low polar carbonyl groups (with dipole moment mu = 2.7 D) retain more extended conformation in MC. This explains why the characteristic viscosities [eta] of MC solutions are much lower for the former polymers ( approximately 0.1 dL/g) with regard to PLGA and PCL solutions whose [eta] is equal to 0.3 and 0.6 dL/g, respectively. The ionization of TMA groups in contact with the water phase leads to the irreversible adsorption of Eudragits at the MC/water interface and to high decrease of the interfacial tension gamma (down to 4 mN/m for the 5% MC solutions). Whereas PLGA and PCL possessing low polar carbonyl groups adsorb poorly at the MC/water interface exhibiting gamma congruent with 28 mN/m. Higher stability of spread monolayers of Eudragits (pi* approximately 40 mN/m) with regard to PLGA and PCL (pi* < 20 mN/m) correlates well with higher interfacial activity of the former with regard to the later. The higher surface potential DeltaV of Eudragits (0.9 V) with regard to PLGA (0.3 V) and PCL (0.4V) is explained by the formation of electric double layer (DL) by the former, whereas the later contribute to the DeltaV only by cumulative dipole moments of carbonyl groups. The experimental values of surface potentials correlate well with the Gouy-Chapman model of the DL and the Helmholtz model of the monolayer. The ensemble of experimental results leads to the conclusion that higher emulsifying and stabilizing ability of Eudragits with regard to PLGA and PCL is due to higher adsorption activity of the former which form the corona of polymeric chains with ionized TMA groups around the droplets. It can be postulated that Eudragit polymers have good surface active properties which may allow manufacturing of biocompatible nanoparticles by emulsification-solvent evaporation method without surfactants.

In vitro characteristics of poly(lactic-co-glycolic acid) microspheres incorporating gelatin particles loading basic fibroblast growth factor

AIM

To construct a sustained drug release system for basic fibroblast growth factor (bFGF). With this special system, bFGF can be used to repair an injured peripheral nerve, injured spinal cord, or as a carrier for other drugs that need to be released over a long time.

METHODS

Microsphere composite was prepared by encapsulating bFGF into gelatin particles with poly(lactic-co-glycolic acid) (PLGA) as its outer-coating. The encapsulation was conducted by a phase separation method.

RESULTS

The average diameter of the gelatin particle-PLGA microsphere composite was 5-18 mum, and bFGF-loading efficiency was up to 80.5%. The bFGF releasing experiment indicated that this new composite system could release bFGF continuously and protect bFGF from denaturation.

CONCLUSION

A modified approach was successfully employed to develop a biodegradable system for sustained release of the drug of bFGF in vitro.

Characterization of polymeric poly(ε-caprolactone) injectable implant delivery system for the controlled delivery of contraceptive steroids

Contraceptive steroids levonorgestrel (LNG) and ethinyl estradiol (EE) have been encapsulated with poly(epsilon-caprolactone) (PCL) microspheres using a w / o /w double emulsion method. The microspheres prepared were smooth and spherical, with a mean size from 8-25 microm. In vitro release profiles of microspheres showed a trend of increasing initially at the first week, and thereafter the release was sustained. At the end of the seventh week LNG/EE from 1:5 and 1:10 PCL microspheres were 60 and 48%, 52 and 46%, respectively. An in vitro degradation study shows that at the 20th week the microspheres maintained the surface integrity. The PCL microspheres showed a triphasic in vivo release profile with an initial burst effect due to the release of the steroid adsorbed on the microsphere surface, a second sustained release phase due to the steroid diffusion through the pores or channels formed in the polymer matrix, and third phase due to polymer bioerodible. Histological examination of PCL microspheres injected intramuscularly into thigh muscle of a rat showed a minimal inflammatory reaction demonstrating that contraceptive steroid-loaded microspheres were biocompatible. The level of inflammatory cytokines determined by immunostaining for IL-1alpha, the tissue response to formulations at the first week was considered mild, whereas at the end of the 20th week the inflammatory response ceased. Thus, this study helped us to evaluate the feasibility of using these microspheres as a long-acting biodegradable drug delivery system for contraceptive steroids.

Characterization of biodegradable drug delivery vehicles with the adhesive properties of leukocytes II: effect of degradation on targeting activity

The site-specific expression of selectins (P- and E-selectin) on endothelial cells of blood vessels during inflammation provides an opportunity for the targeted delivery of anti-inflammatory drugs to sites of chronic inflammation. It is well documented that the selectins mediate the initial interaction (rolling) of leukocytes in an inflamed vessel by binding to carbohydrate-presenting counter-receptors displayed on leukocytes. Previous work in our laboratory has shown that artificial capsules with the adhesive properties of leukocytes can be made by attaching leukocyte adhesive ligands to polymer microspheres (Biomaterials 23(10) (2002) 2167). Specifically, we showed that drug-loaded poly (lactic-co-glycolic-acid) (PLGA) microspheres coated with biotinylated-Sialyl LewisX (sLeX), a carbohydrate that serves as a ligand to selectins, mimic the adhesive behavior of leukocytes on selectins in flow chambers, displaying slow rolling under flow, suggesting that these drug-loaded particles can potentially target inflammatory sites in vivo. Since the effectiveness of this delivery system might depend on the degradation of polymer microspheres as well as the degradation of sLeX molecules, we measured the effect of polymer and ligand degradation on the adhesiveness of microspheres over time. We show that degrading sLeX microspheres maintain the ability to recognize selectin surfaces under flow for at least 2 weeks and that the ability to sustain recognition depends upon the extent at which microspheres are loaded. We also show that microsphere rolling velocity increases as microsphere degrade and that this increase is due to a combination of increase in average microsphere size and loss of sLeX molecules on microsphere surface--a result of microsphere degradation confirmed by flow cytometry. Control experiments show that microsphere, not sLeX, degradation limits the lifetime of our targeted delivery system; therefore, factors affecting degradation such as type of polymer, type of drug, extent of drug loading and microsphere size, provide an opportunity for engineering the time-scale of activity for the delivery system.

Oil core-polymer shell microcapsules prepared by internal phase separation from emulsion droplets. I. Characterization and release rates for microcapsules with polystyrene shells

Microcapsules with an oil core surrounded by a polymeric shell have been prepared by the controlled phase separation of polymer dissolved within the oil droplets of an oil-in-water emulsion. The dispersed oil phase consists of the shell polymer (polystyrene), a good solvent for the polymer (dichloromethane), and a poor solvent for the polymer (typically hexadecane). Removal of the good solvent results in phase separation of the polymer within the oil droplets. If the three interfacial tensions between the core oil, the shell-forming polymer, and the continuous phase are of the required relative magnitudes, a polymer shell forms surrounding the poor solvent. A UV-responsive organic molecule was added to the oil phase, prior to emulsification, to investigate the release of a model active ingredient from the microcapsules. This molecule should be soluble in the organic core but also have some water solubility to provide a driving force for release into the continuous aqueous phase. As the release rate of the active ingredient is a function of the thickness of the polymeric shell, for controlled release applications, it is necessary to control this parameter. For the preparative method described here, the thickness of the shell formed is directly related to the mass of polymer dissolved in the oil phase. The rate of volatile solvent removal influences the porosity of the polymer shell. Rapid evaporation leads to cracks in the shell and a relatively fast release rate of the active ingredient. If a more gentle evaporation method is employed, the porosity of the polymer shell is decreased, resulting in a reduction in release rate. Cross-linking the polymer shell after capsule formation was also found to decrease both the release rate and the yield of the active ingredient. The nature of the oil core also affected the release yield.

Development of implant tablet for a week-long sustained release

An implant tablet for a week-long sustained release was developed by the direct compression method using poly-DL-lactic acid (PLA) and poly(DL-lactic acid-co-glycolic acid) copolymer (PLGA) as a matrix and phenol red (PR) as a model drug. The in vitro release was affected by formulations, especially by drug content and polymer species. The release rate correlated with the rate of absorption of water. The implant tablet (30 mg) containing 1 mg of PR, prepared using PLGA (MW 10,000; lactic acid/glycolic acid=1:1, mol/mol) by compression at 50 kg/cm(2) for 10 s, was found to efficiently exhibit a week-long sustained release in vitro, and applied in vivo. The remaining amount or plasma concentration of PR after s.c. administration of the implant tablet to rats demonstrated that the implant tablet showed a week-long sustained release in vivo. The present implant tablet is suggested to be useful as a drug delivery system for supplying drugs for approximately 1 week.

Mechanistic evaluation of the glucose-induced reduction in initial burst release of octreotide acetate from poly(d,l-lactide-co-glycolide) microspheres

One major obstacle for development of injectable biodegradable microspheres for controlled peptide and protein delivery is the high initial burst of drug release occurring over the first day of incubation. We describe here the significant reduction in initial burst release of a highly water-soluble model peptide, octreotide acetate, from poly(D,L-lactide-co-glycolide) microspheres by the co-encapsulation of a small amount of glucose (e.g., 0.2%w/w), i.e., from 30+/-20% burst - glucose to 8+/-3% + glucose (mean+/-SD, n=4). This reduction is unexpected since hydrophilic additives are known to increase porosity of microspheres, causing an increase in permeability to mass transport and a higher burst. Using the double emulsion-solvent evaporation method of encapsulation, the effect of glucose on initial burst in an acetate buffer pH 4 was found to depend on polymer concentration, discontinuous phase/continuous phase ratio, and glucose content. Extensive characterization studies were performed on two microsphere batches, +/-0.2% glucose, to elucidate the mechanism of this effect. However, no significant difference was observed with respect to specific surface area, porosity, internal and external morphology and drug distribution. Continuous monitoring of the first 24-h release of octreotide acetate from these two batches disclosed that even though their starting release rates were close, the microspheres + glucose exhibited a much lower release rate between 0.2 and 24h compared to those - glucose. The microspheres + glucose showed a denser periphery and a reduced water uptake at the end of 24-h release, indicating decreased permeability. However, this effect at times was offset as glucose content was further increased to 1%, causing an increase in surface area and porosity. In summary, we conclude that the effect of glucose on initial burst are determined by two factors: (1) increased initial burst due to increased osmotic pressure during encapsulation and drug release, and (2) decreased initial burst due to decreased permeability of microspheres.

Effect of the size of biodegradable microparticles on drug release: experiment and theory

The aim of this study was to investigate the effect of the size of biodegradable microparticles (monolithic dispersions) on the release rate of an incorporated drug in a quantitative way. 5-Fluorouracil-loaded, poly(lactic-co-glycolic acid)-based microparticles were prepared with a solid-in-oil-in-water solvent extraction technique. In vitro drug release from different-sized particle fractions was measured in phosphate buffer pH 7.4. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and size exclusion chromatography (SEC) were used to monitor the degradation behavior of the polymer and morphological changes of the microparticles upon exposure to the release medium. Based on these experimental results, an appropriate mathematical theory was identified and used to get further insight into the underlying physical and chemical processes, which are involved in the control of drug release. Interestingly, the relative as well as the absolute release rate of the drug increased with increasing microparticle radius, despite of the increasing diffusion pathways. SEC, DSC and SEM analysis revealed that the degradation behavior of the matrix forming polymer was not significantly affected by the size of the devices and that autocatalytic effects do not seem to play a major role. Importantly, the initial drug loading significantly increased with increasing radius of the drug delivery system. Thus, large microparticles became more porous during drug release than small microparticles, leading to higher apparent diffusivities and drug transport rates. This effect overcompensated the effect of the increasing diffusion pathways with increasing microparticle radius, resulting in increased drug release rates with increasing device dimension. The applied mathematical model, considering drug diffusion with non-constant diffusivities (to account for polymer degradation) was able to quantitatively describe the observed drug release patterns. Importantly, an exponential relationship could be established between the diffusion coefficient and the initial loading of the drug. Based on this dependency, it was possible to predict the resulting drug release kinetics for arbitrary microparticle sizes in a quantitative way.

The encapsulation of ribozymes in biodegradable polymeric matrices

Ribozymes are catalytic RNA that bind and cleave specific regions of target RNA. Therefore, protein synthesis by the target RNA may be specifically inhibited by ribozymes. However, ribozymes are rapidly cleared from plasma so effective treatment of proliferative diseases may rely on the repeated administration of these agents to maintain therapeutic ribozyme concentrations. Therefore, the objective of this study was to encapsulate ribozymes in injectable polymeric paste and microsphere formulations to allow for the controlled release of these agents over extended periods of time. Ribozymes were effectively encapsulated in poly(L-lactic acid) (PLLA) and poly(lactic-co-glycolic) (PLGA) microspheres in various size ranges using a modified water-in-oil-in-water emulsion system and in poly(epsilon-caprolactone) (PCL) pastes by physical blending. These formulations released non-degraded ribozymes, in vitro, in a controlled manner. PLLA microspheres released the ribozymes rapidly whereas PLGA released drugs more slowly. The release rate of ribozymes from PCL pastes could be effectively controlled by altering the loading concentration of ribozymes in the paste. These polymeric injectable formulations of ribozymes may allow for the extended treatment of localized disease sites, such as cancer and arthritis, without the need for repeated dosing.

Biodegradable scleral plugs for vitreoretinal drug delivery

Intraocular controlled drug release is one way to facilitate drug efficacy and decrease side effects that occur with systemic administration. Vitreoretinal drug delivery with the biodegradable scleral plug has been investigated. The scleral plug, which is made of biodegradable polymers and drugs, can be implanted at the pars plana using a simple procedure, and it gradually releases effective doses of drugs with polymer biodegradation for several months. The release profiles of the drugs were dependent on the kind of polymers used, their molecular weights, and the amount of drug in the plug. The plugs are effective for treating vitreoretinal diseases such as proliferative vitreoretinopathy. The implantation site was replaced with connective tissue. Electroretinography and histologic studies revealed little retinal toxicity. This implantable scleral plug was supposed to be advantageous for diseases such as cytomegalovirus retinitis that respond to repeated intravitreal injections and for vitreoretinal disorders that require vitrectomy.

Paclitaxel loaded poly(L-lactic acid) microspheres: properties of microspheres made with low molecular weight polymers

Microspheres were prepared from poly(L-lactic acid) polymers having molecular weights between 500 and 50k g/mol. The polymers were synthesized using two initiator molecules, L-lactic acid oligomer (PLLA-LA) or stearyl alcohol (PLLA-SA). For both PLLA-LA and PLLA-SA polymers, glass (Tg) and melting (Tm) transition temperatures and enthalpy of melting all increased as the polymer molecular weight increased. PLLA-SA showed the greatest change in Tg (-13 to 54 degrees C) as molecular weight increased from 500 to 10k x g/mol, compared to 25 to 55 degrees C for PLLA-LA polymers. Changes in Tm and enthalpy of melting with increasing molecular weight were similar for both PLLA-LA and PLLA-SA. Paclitaxel release from 30% paclitaxel loaded microspheres in the size range of 50-90 microm was affected by these changes in polymer properties as molecular weight increased. As the molecular weight increased from 2k to 50k x g/mol the amount of drug released from microspheres over 14 days decreased from 76 to 11% of the initial drug load. The release profiles were consistent with a diffusion controlled mechanism provided a two-compartment model was employed. According to this model, the total amount of 'available' drug (compartment 1) was released by diffusion in 14 days while the remainder (compartment 2) was confined within the polymeric matrix and could not diffuse out at a measurable rate. Following the in vitro release study, microsphere made from 2k-10k g/mol polymers showed significant signs of disintegration whereas 50k x g/mol polymer microspheres remained intact.

Neutrophil activation by plasma opsonized polymeric microspheres: inhibitory effect of pluronic F127

The phagocytosis of drug-loaded polymeric microspheres by white blood cells, such as neutrophils or mononuclear cells, represents the major clearance mechanism by which this foreign material is eliminated from the body. The process of phagocytosis requires the activation of the white blood cells by the microsphere surface, followed by binding and engulfment. Phagocytosis may result in the removal of the microspheres from the blood or the disease site and an inflammatory response. Therefore, we have studied the level of neutrophil activation by microspheres ( +/- opsonization) manufactured from various biomaterials or polymers. Polymer microspheres with equivalent size distributions were made from poly (DL-lactic acid) (PLA), poly(epsilon-caprolactone) (PCL), poly(methyl methacrylate) (PMMA) or a 50 : 50 blend of PLA: poly(ethylene-co-vinyl acetate) (PLA: EVA). Neutrophils were isolated from human blood and activation of these cells by microspheres was measured by chemiluminescence (CL). All four types of microspheres induced only low levels of CL, however these levels were enhanced significantly if the microspheres were pretreated with plasma or IgG suggesting an opsonization effect. The adsorption of IgG or proteins from plasma was confirmed by polyacrylamide gel electrophoresis (SDS-PAGE). The poloxamer Pluronic F127 inhibited the opsonization effect of IgG and plasma on all four types of microspheres and inhibited protein adsorption as measured by SDS-PAGE. Since neutrophil activation is part of the inflammation process in vivo, these in vitro data suggest that all four types of microspheres are likely to be inflammatory if injected into body compartments containing plasma-derived fluids. Pretreatment of the microspheres with Pluronic F127 may reduce the inflammatory potential of the microspheres.

In vitro and in vivo evaluation of a somatostatin analogue released from PLGA microspheres

The purpose of this study was to design poly(lactide-co-glycolide) (PLGA) microspheres for the continuous delivery of the somatostatin analogue, vapreotide, over 2-4 weeks. The microspheres were produced by spray-drying and the desired characteristics, i.e. high encapsulation efficiency and controlled release over 2-4 weeks, achieved through optimizing the type of polymer, processing solvent, and co-encapsulated additive. The in vitro release was tested in fetal bovine serum preserved with 0.02% of thiomersal. Furthermore, formulations were injected intramuscularly into rats to obtain pharmacokinetic profiles. Encapsulation efficiency was between 34 and 91%, depending on the particular formulation. The initial peptide release (within 6 h) was lowest, i.e. <20%, when acetic acid was used as processing solvent and highest, i.e. 57%, with dichloromethane. The various co-encapsulated additives generally lowered the encapsulation efficiency by 15-30%. The best formulation in terms of low burst and effective drug serum levels (>1 ng/ml) over 21-28 days in rats was the one made with end-group uncapped PLGA 50:50, the solvent acetic acid and the additive polyethyleneglycol. In conclusion, the optimization of formulation parameters allowed us to produce vapreotide-loaded PLGA microspheres of suitable characteristics for therapeutic use.

Pharmacokinetics of prolonged-release CPT-11-loaded microspheres in rats

CPT-11-containing microspheres composed of poly-D,L-lactic acid or poly (D,L-lactic acid-co-glycolic acid) copolymers were prepared by an oil-in-water evaporation method. The size and shape of the microspheres were examined, and the drug release rates were analyzed from the in vitro release profiles. CPT-11 aqueous solution was intravenously or intraperitoneally injected at 10 mg/kg, and microspheres were intraperitoneally administered at 50 mg eq CPT-11/kg in rats. The microspheres had an average diameter of around 10 microm and their shape was spherical. All the microspheres contained CPT-11 in a lactone form, and their drug contents and release profiles were basically similar to those of previous microspheres. After i.v. injection of CPT-11 solution, the CPT-11 plasma concentration decreased quickly, SN-38 decreased slowly at a much lower level, and SN-38 glucuronide (SN-38G) declined very slowly at a higher level than SN-38. The plasma concentration of CPT-11 reached a maximum at 30 min after i.p. administration of CPT-11 solution. The area under the plasma concentration-time curve (AUC) of CPT-11 after i.p. administration was somewhat lower compared with that after i.v. administration, but the plasma concentration-time profiles of SN-38 and SN-38G were nearly identical between i.v. and i.p. administration. An i.p. administration of the microspheres resulted in gradually increasing or almost constant CPT-11 levels. The levels of SN-38 were also stable during the observation period (4 days) except for the slowest releasing microsphere in which SN-38 was not detected after 24 h following administration. Intraperitoneal administration of any of the microspheres resulted in stable and similar levels of SN-38G after 24 h following administration. When judging from apparent simple pharmacokinetic analysis, an inconsistency was found between the in vitro drug release and the plasma level to a fair extent, but overall the in vivo drug release rate from microspheres was considered parallel to the in vitro one. The microspheres showing a faster release of CPT-11 exhibited higher plasma levels of CPT-11 and SN-38, explaining the previous results that efficacy was better when the in vitro release rate was higher. That the SN-38 level could be attained to a certain extent even at the range of modest or low plasma concentration of CPT-11 in each administration may be related to the non-linear metabolic conversion from CPT-11 to SN-38.

Influence of additives on the release profile of nifedipine from poly(DL-lactide-co-glycolide) microspheres

Nifedipine-containing poly(DL-lactide-co-glycolide) (PLGA) microspheres of various sizes and drug contents were prepared by the solvent evaporation method. The in vitro release profiles of nifedipine from PLGA microspheres and the degradation pattern of the polymer were evaluated. Four additives were incorporated in the microspheres: two non-fatty plasticizers: diethylphthalate and triacetin, and two fatty substances: isopropyl myristate and Myvacet. Diethylphthalate and Myvacet increased the nifedipine release rate while isopropyl myristate and triacetin had no influence on it. Triacetin seems to be very poorly incorporated into the microspheres. These additives did not modify the degradation rate of the polymer. Differential scanning calorimetry detected a decrease of the glass transition temperature of diethylphthalate-containing microspheres, a small variation with Myvacet, and very little change when triacetin or isopropyl myristate were incorporated. This variation of the glass transition temperature (Tg) tends to imply that nifedipine is released by a diffusion process through the polymer matrix which is enhanced when additives decrease the Tg. Scanning electron microscopy allowed the vizualization of the highly porous structure of microspheres containing the oily substances, and the unchanged smooth surface of diethylphthalate-containing microspheres.

Sustained release dosage of thyrotropin-releasing hormone improves experimental Japanese encephalitis virus-induced parkinsonism in rats

Thyrotropin-releasing hormone (TRH) has been reported to have some possibilities toward the treatment of affective CNS disorders. However, long term treatments with daily injections are often required. Effects of TRH-SR (sustained release microspheres of TRH) which is encapsulated in copoly (dl-lactic/glycolic acid) using an in-water drying method were investigated in experimental Japanese encephalitis virus (JEV)-induced post-encephalitic parkinsonism rats by a pole test and high performance liquid chromatography (HPLC) with an electrochemical detector (ECD). We have already reported that in adult Fischer rats killed 12 weeks after infection with JEV at the age of 13 days a marked decrease of tyrosine hydroxylase-positive neurons was found in the bilateral substantia nigra. TRH-SR (3 mg/kg per 2 weeks, 4 times injections, subcutaneous [s.c.]) improved bradykinesia observed in the JEV-induced parkinsonism rats. Dopamine (DA) concentrations in the JEV-infected rats were profoundly reduced in the striatum as compared with controls. TRH-SR (3 mg/kg, once, s.c.) increased DA in the striatum 7 days after the injection. Although the pathomechanism of post-encephalitic parkinsonism is different from that of Parkinson's disease and TRH possesses a variety of CNS effects as well, these results suggest that TRH-SR play a possible role in the treatment of Parkinson's disease in addition to post-encephalitic parkinsonism as a supportive drug of L-DOPA.

Development and evaluation in vivo of a long-term delivery system for vapreotide, a somatostatin analogue

In recent years peptides and proteins have received much attention as candidate drugs. For many peptides, particularly hormones, it is desirable to release the drug continuously at a controlled rate over a period of weeks or even months. Polylactic acid and poly (lactic-co-glycolic) acid are well known biocompatible biodegradable materials with wide applications including the design of controlled-release systems for pharmaceutical agents. Polylactic acid implants containing vapreotide were prepared by an extrusion method and drug release was evaluated in vivo in rats using an RIA method The development of an injectable, biodegradable depot formulation of a somatostatin analogue (vapreotide) is described which ensures satisfactory peptide blood level in rats over approximately 250 days. A modification of this formulation by means of a wear coating allows minimisation of the initial burst a feature rarely discussed.