Controlled release of a luteinizing hormone-releasing hormone analogue from poly(d,l-lactide-co-glycolide) microspheres

Niridazole biodegradable inserts for local long-term treatment of periodontitis: possible new life for an orphan drug

Periodontal pocket inserts of niridazole (NZ) made with Resomer(R) (grades RG 503H and RG858, designated as RH and RG, respectively) were studied. Various formulation variables were evaluated to obtain a biodegradable delivery systems showing device degradation and drug depletion parallel to each other in vitro. Drug release from the prepared inserts was evaluated using a static dissolution setup (for 1 month). Incorporation of 3 parts of RG in 1 part of RH inserts caused a 50% decrease in the initial release rate. The RH-NZ inserts showed a spurt in release around the 10th day of the study, which coincided with the decrease in device weight, suggesting onset of device degradation. Pilot-scale clinical trials in 12 patients indicated improvements in clinical indices from the baseline values. The average pocket depth was reduced significantly (alpha = 0.05) from 6.34 +/- 1.86 mm at baseline to 5.94 +/- 0.28 mm after 28 days of treatment.

Hyperbranched polymers as drug carriers: microencapsulation and release kinetics

The aim of this work was to study the feasibility of hyperbranched polymers as drug carriers by employing different microparticle formation methods and the influence of loading methods on release kinetics. Commercially available hyperbranched polyester (Perstorp) and three polyesteramides (DSM) were loaded with the pharmaceutical acetaminophen. The gas antisolvent precipitation (GAS), the coacervation, and the particles from gas saturated solutions (PGSS) are among conventional processes that were used to prepare microparticles of drug-loaded hyperbranched polyesters for the first time. For preparing solid dispersions of drug-loaded hyperbranched polyesteramides the solvent method was applied. Infrared (IR) and differential thermal analysis (DTA) studies suggest that acetaminophen is partly dissolved in the polymer matrix and partly crystallized outside the polymer matrix. For acetaminophen-loaded polyesters prepared by the GAS method, the presence of free drugs is predominant when compared to microparticles prepared by the coacervation method. This event disappears for microparticles prepared by the PGSS method. Moreover, the release of drug from drug-loaded Bol-GAS is biphasic, where the initial burst (48%), indicating the presence of unincorporated drugs, is followed by a slow-release phase, suggesting the diffusion of drug through polymer matrices. The release of drugs from drug-loaded Bol-PGSS do not show this behavior since the drug is better dissolved or dispersed in polymer matrices. In the case of drug-loaded polyesteramides, coevaporates prepared from 3 hyperbranched structures (H1690, H1200, and H1500) using the solvent method result in different release kinetics. The hydrophobic characteristic of hyperbranched polyesteramide H1500 shows the biphasic release kinetic whereas the drug released from hydrophilic matrices H1690 and H1200 exhibits fast release comparable to that of pure drug.

Drug delivery from ocular implants

Developing an intraocular drug delivery system (DDS) is urgently needed because most vitreoretinal diseases are refractory to conventional pharmacological approaches; eye drops and systemically administered drugs cannot deliver therapeutic drug concentrations into vitreoretinal tissue. Intraocular DDSs address this problem. Intraocular sustained-drug release via implantable devices or injectable microparticles has been investigated to treat vitreoretinal diseases. A nonbiodegradable implant was first used in 1996 for cytomegalovirus retinitis secondary to the acquired immunodeficiency syndrome. Biodegradable implants, composed of hydrophilic or hydrophobic polymers, in the shape of rods, plugs, discs or sheets have been investigated. An injectable rod is presently being assessed in a Phase III trial to treat macular oedema secondary to diabetic retinopathy or branch-retinal vein occlusion. Intraocular DDSs using a biodegradable implant may soon be successfully used to treat serious intraocular disorders.

Solvent exchange method: a novel microencapsulation technique using dual microdispensers

PURPOSE

A new microencapsulation method called the "solvent exchange method" was developed using a dual microdispenser system. The objective of this research is to demonstrate the new method and understand how the microcapsule size is controlled by different instrumental parameters.

METHOD

The solvent exchange method was carried out using a dual microdispenser system consisting of two ink-jet nozzles. Reservoir-type microcapsules were generated by collision of microdrops of an aqueous and a polymer solution and subsequent formation of polymer films at the interface between the two solutions. The prepared microcapsules were characterized by microscopic methods.

RESULTS

The ink-jet nozzles produced drops of different sizes with high accuracy according to orifice size of a nozzle, flow rate of the jetted solutions, and forcing frequency of the piezoelectric transducers. In an individual microcapsule, an aqueous core was surrounded by a thin polymer membrane; thus, the size of the collected microcapsules was equivalent to that of single drops.

CONCLUSIONS

The solvent exchange method based on a dual microdispenser system produces reservoir-type microcapsules in a homogeneous and predictable manner. Given the unique geometry of the microcapsules and mildness of the encapsulation process, this method is expected to provide a useful alternative to existing techniques in protein microencapsulation.

Drug delivery systems for vitreoretinal diseases

The eye has an environment that is specific unto itself in terms of pharmacokinetics: the inner and outer blood-retinal barriers separate the retina and the vitreous from the systemic circulation and vitreous body, which physiologically has no cellular components, occupies the vitreous cavity, an inner space of the eye, and reduces practical convection of molecules. Considering this, development of a drug delivery system (DDS) is becoming increasingly important in the treatment of vitreoretinal diseases not only to facilitate drug efficacy but also to attenuate adverse effects. The DDS has three major goals: enhances drug permeation (e.g., iontophoresis and transscleral DDS), controls release of drugs (e.g., microspheres, liposomes, and intraocular implants), and targets drugs (e.g., prodrugs with high molecular weight and immunoconjugates). Comprehensive knowledge of these should lead to development of innovative treatment modalities.

In vitro transdermal iontophoretic delivery of leuprolide under constant current application

Transdermal delivery of Leuprolide, a nonapeptide LHRH agonist, was studied using constant current iontophoresis to explore methods for improving iontophoretic efficiency and determine the feasibility of delivery of therapeutic doses of the drug. Universal buffer consisting of citrate, phosphate and borate was used to carry out in vitro permeation experiments with heat separated human epidermis at pH 4.5 and 7.2. In addition, the effect of substituting this buffer with a macromolecular electrolyte, polymaleic acid, on the drug flux and the transference number was studied. Current densities from 0.5 to 2.3 microA/cm2 were used requiring moderate potential differences between 60 and 420 mV to be applied thus limiting irreversible epidermal membrane alterations. The rather high electrical resistance of the epidermis of the order of 200 kohms cm2 was related to the sub-physiological electrolyte concentration. Resistance was continuously monitored to guarantee barrier integrity of the membrane. The permeation rate increased linearly with the current density for the universal buffer and was at pH 7.2 almost double that at pH 4.5 despite the greater ionic valence of the drug at pH 4.5 compared to pH 7.2; this being because of the opposite direction of the electroosmotic flow at the two pH values. Drug transference number at both pH values was approximately 0.5%. Replacement of the universal buffer with polymaleic acid yielded higher drug permeation rates and increased its transference number at comparable pH. Transference number, however, was still approximately 1% at the highest current density, showing that concomitant ions from added electrolyte or extracted from the skin and the electrodes accounted for 99% of the total current. Further, transference number of the drug with polymaleic acid appeared to increase with current density. The fluxes obtained for both electrolyte systems with the present experimental arrangement could be extrapolated to deliver therapeutically relevant doses of the drug.

Preparation and characterization of injectable microspheres of contraceptive hormones

Present study describes the development of a new formulation of levonorgestrel and ethinylestradiol based on double emulsion-solvent evaporation technique using poly(epsilon-caprolactone) (PCL) as biodegradable polymer. The effect of polymer concentration on microspheres and entrapment of drug into microspheres were studied. PCL was selected because of its hydrophobicity and advantages over other biodegradable polymers. Characterization of biodegradable polymer used for controlled drug delivery is essential to ensure reproducibility of in vitro and in vivo performances. The selected characterisation techniques established for PCL microspheres include its loading and entrapment efficiencies, DSC to analyse thermal behaviour, SEM to observe surface morphology, drug content of microspheres and in vitro release of drugs from microspheres. The SEM reports showed that microspheres were with smooth surface and DSC thermograms revealed no interaction between drug and polymer. The entrapment was found to be 58 and 47% for 1:10 and 1:5 batches and in vitro release studies showed that about 69.7% of LNG and 66.7% of EE from 1:10 batch and about 80% of LNG and 75.5% of EE from 1:5 batch for 150 days.

Synthesis and properties of star-shaped polylactide attached to poly(amidoamine) dendrimer

Star-shaped polylactide was synthesized by bulk polymerization of lactide with poly(amidoamine) (PAMAM) dendrimer as initiator, which was marked as PAMAM-g-PLA for simplicity. The nonlinear architecture of PAMAM-g-PLA was confirmed by gel permeation chromatograph, nuclear magnetic resonance, and differential scanning calorimetry analysis. Unlike the linear polylactide (PLA) with similar molecular weight, PAMAM-g-PLA had a higher hydrophilicity and a faster degradation rate because of shortened polymer chains and increased polar terminal endgroups due to its branch structure. The highly branched structure significantly accelerated the release of water-soluble bovine serum albumin from PAMAM-g-PLA microspheres, whereas the linear PLA with similar molecular weight exhibited an initial time lag release. This star polymer may have potential applications for hydrophilic drug delivery in tissue engineering, including growth factor and antibodies to induce tissue regeneration, by adjusting the chain lengths of PLA branches.

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.

Preparation and evaluation of poly(L-lactic acid) microspheres containing rhEGF for chronic gastric ulcer healing

Biodegradable microspheres containing recombinant human epidermal growth factor (rhEGF) were prepared using poly(L-lactic acid) by a solvent evaporation method based on multiple w/o/w emulsion. Encapsulation efficiency and initial release were influenced by the amount of polymer, inner water phase volume and osmotic pressure difference between inner water phase and outer water phase. The effect of osmotic pressure difference between inner water phase and outer water phase in w/o/w emulsion on particle size, porosity and in vitro release of rhEGF from microspheres were also studied. Microspheres prepared with the optimized osmotic pressure, polymer amount and inner water volume produced 21% initial release on the first day with 92% encapsulation efficiency. The blood concentration of rhEGF was maintained at constant levels for 9-11 days after a single subcutaneous (s.c.) administration of rhEGF microspheres. The gastric ulcer healing effect of a single s.c. administration of rhEGF microspheres was increased 1.44-fold compared with twice a day s.c. administration of rhEGF saline solution after 11 days. The enhanced curative ratio of rhEGF loaded microspheres may be due to the optimized osmotic pressure, high encapsulation efficiency and sustained release pattern.

Translocation of drug particles in HPMC matrix gel layer: effect of drug solubility and influence on release rate

The aim of this work was to study the release mechanisms of drugs having different solubility (buflomedil pyridoxalphosphate 65%, sodium diclofenac 3.1%, nitrofutantoin 0.02% w/v,) from hydroxypropyl methylcellulose (HPMC) matrices by concomitantly studying swelling, diffusion and erosion fronts movement and drug delivery. The main goal was to clarify the role played by polymer swelling in drug transport. The results showed that the rate and amount of drug released from swellable matrices was dependent not only from drug dissolution and diffusion but also from solid drug translocation in the gel due to polymer swelling. In fact, as drug solubility decreased, the slower drug dissolution rate in the gel layer allowed drug particles to be transported close to the matrix erosion front. The presence of solid particles in the gel reduced the swelling and the entanglement of polymer chains and affected the resistance of gel towards erosion. As a consequence, the matrix became more erodible. The erosive delivery accelerated after the matrix had been completely transformed into the rubbery state, particularly when a considerable amount of solid drug particles remained in the gel phase.

Salt and cosolvent effects on ionic drug loading into microspheres using an O/W method

Salt effects on aqueous solubility and microsphere entrapment efficiency of a model ionic drug (quinidine sulfate) were studied. Poly-D,L-lactic acid (PLA) microspheres were prepared using an O/W solvent evaporation method with various electrolytes added in different concentrations to the aqueous phase. Salts affect microsphere drug loading by changing the aqueous solubility of both the drug and the organic solvent (dichloromethane, DCM). Quinidine sulfate solubility was depressed by either a common ion effect (Na(2)SO(4)) or by formation of new, less soluble drug salts (e.g., bromide, perchlorate, thiocyanate) for which solubility products (K(sp)) were estimated. Inorganic salts depress DCM aqueous solubility to different extents as described by the Hofmeister series. NaClO(4) and NaSCN depressed drug solubility to the highest extent, resulting in microspheres with high drug loading (e.g., >90%). Other salts such as Na(2)SO(4) did not depress quinidine sulfate solubility to the same extent and did not improve loading. The use of a cosolvent (ethanol) in the organic phase improved microsphere drug loading and resulted in a uniform microsphere drug distribution with smooth release profiles.

In vitro protein release and degradation of poly-dl-lactide-poly(ethylene glycol) microspheres with entrapped human serum albumin: quantitative evaluation of the factors involved in protein release phases

PURPOSE

To quantitatively evaluate the correlations between the amount of initial burst release and the surface-associated protein, and between the onset time for the second burst release and the matrix polymer degradation.

METHODS

Human serum albumin (HSA) was microencapsulated in polylactide (PLA) and poly-dl-lactide-poly(ethylene glycol) (PELA) with PEG contents of 5, 10, 20, and 30%, respectively, using the solvent extraction procedure based on formation of double emulsion w/o/w. Microspheres with similar particle size (1.7-2.0 microm), similar protein entrapment (2.1-2.8%) but different surface-associated proteins (9.3-53.6%) were used to evaluate the in vitro matrix degradation and protein release profiles. Degradation was characterized by studying the intrinsic viscosity decrease, medium pH change, and weight loss of the microspheres.

RESULTS

The matrix degradation and protein release profiles were highly dependent on the polymer composition of the microspheres. Faster decreases in the intrinsic viscosity of recovered matrix polymer, the microspheres weight, and the pH of degradation medium, and earlier onsets for the break in intrinsic viscosity reduction and the mass loss were detected for PELA microspheres with higher PEG content. The hydration and swelling of microspheres matrix contributed greatly to the degradation of matrix polymer. The HSA release showed triphasic profile and involved two mechanisms for all the microsphere samples. Smaller amount of initial burst release, larger gradual release rate, and earlier onset for the second burst release were observed for HSA from matrix polymer with higher PEG content. The extent of the initial burst release was quantitatively related with the surface-associated protein. The second burst release of HSA was observed to occur within 1 week after the onset for mass loss, which was also the break in the intrinsic viscosity reduction rate.

CONCLUSION

Protein release profiles could be rationalized by optimizing the matrix polymer degradation and microsphere characteristics.

The manufacturing techniques of various drug loaded biodegradable poly(lactide-co-glycolide) (PLGA) devices

A considerable research has been conducted on drug delivery by biodegradable polymeric devices, following the entry of bioresorbable surgical sutures in the market about two decades ago. Amongst the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) like poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide, poly(lactide-co-glycolide) (PLGA) have generated immense interest due to their favorable properties such as good biocompatibility, biodegradability, and mechanical strength. Also, they are easy to formulate into different devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Also, they have been approved by the Food and Drug Administration (FDA) for drug delivery. This review discusses the various traditional and novel techniques (such as in situ microencapsulation) of preparing various drug loaded PLGA devices, with emphasis on preparing microparticles. Also, certain issues about other related biodegradable polyesters are discussed.

Mechanistic aspects of the release of levamisole hydrochloride from biodegradable polymers

The release of levamisole hydrochloride from poly-DL-lactide-co-glycolide compacts prepared at 5, 10 and 20% drug loading using two different particle size fractions of drug (90-125 and 125-250 microm) was investigated. Release profiles were significantly different from those previously reported for compacts prepared using the base form of the drug. Release was found to occur in a biphasic manner, with an initial fast release phase followed by a slower polymer degradation controlled release phase. The drug release profiles were successfully described by a model combining contributions from a first-order initial release phase and a polymer degradation controlled drug release phase. The fraction of drug released in the initial burst phase (F(B)) was attributed to the dissolution of drug domains situated at the surface of the polymer-drug compact and this fraction tended to increase with increasing drug particle size, as expected from the model. The increase in F(B) with increased loading was attributed to the clumping of dispersed drug particles which effectively increased the proportion of drug linked to the compact surface.

Characterization of co-polymers of lactic and glycolic acid for supercritical fluid processing

Polymers of lactic and glycolic acid are often used for the production of injectible microparticles with controlled drug release. In the variety of processes used for the microparticle formulation, the Aerosol Solvent Extraction System (ASES) is rather special. Microparticle formation and drying take place in one step by precipitating a methylene chloride solution of the polymer in supercritical CO2. This process sets special requirements to the polymers in crystallinity, solubility, and thermal behavior that are best fulfilled by blocked copolymers. This study investigates a number of lactide-co-glycolide polymers with blocked distribution of the co-monomers by NMR spectroscopy and powder diffraction. The molar ratios are determined by 1H-NMR spectroscopy to verify the manufacturer's declarations of the purchased specimens. Additionally, the block length is determined by application of 13C-NMR. Therefore, a method reported in the literature was modified and evaluated in order to calculate the length of lactide and glycolide sequences in the polymer. Furthermore, this study looks at the impact of synthesis conditions on block length and crystallinity, and the impact of the blocking on both, crystallinity and solubility of the polymers.

Effect of polymer/basic drug interactions on the two-stage diffusion-controlled release from a poly(L-lactic acid) matrix

We investigated the effect of drug physico-chemical properties on the release of basic drugs from poly(L-lactic acid) (P(L)LA) cylindrical matrices (rods; 10 mmx1 mm diameter). All the rods were revealed to exhibit two-stage diffusion-controlled release profiles resulting from the transformation of P(L)LA from an amorphous to a semicrystalline state in aqueous medium. On the assumption that interactions between polymer carboxyl residues and basic drugs control the drug release rate, we evaluated the strength of these interactions by the drug partition between the polymer and the aqueous medium. In the first release stage, the drugs diffused through the swollen polymer matrix. The polymer-drug interactions shielded the polymer terminal carboxyl residues, thereby resulting in a less hydrated matrix and consequent diminishment of drug diffusion. In the second release stage, the drugs diffused through the water-filled micropores which had developed as a result of polymer crystallization. The stronger polymer-basic drug interactions reduced the drug diffusion rate by decreasing not only the porosity of the matrix, but also the drug partition to the water-filled micropores. It was also found that the fractional drug release rate in the second stage increased with drug content of the rod at the pH where both the polymer carboxyl residues and the drugs were ionized. Since the polymer-drug interactions must be close to saturation with increasing drug content, we believe this result to be due to an increase in the ratio of the drug partition to the water-filled micropores.

A heterogeneously structured composite based on poly(lactic-co-glycolic acid) microspheres and poly(vinyl alcohol) hydrogel nanoparticles for long-term protein drug delivery

PURPOSE

To prepare a heterogeneously structured composite based on poly (lactic-co-glycolic acid) (PLGA) microspheres and poly(vinyl alcohol) (PVA) hydrogel nanoparticles for long-term protein drug delivery.

METHODS

A heterogeneously structured composite in the form of PLGA microspheres containing PVA nanoparticles was prepared and named as PLGA-PVA composite microspheres. A model protein drug, bovine serum albumin (BSA), was encapsulated in the PVA nanoparticles first. The BSA-containing PVA nanoparticles was then loaded in the PLGA microspheres by using a phase separation method. The protein-containing PLGA-PVA composite microspheres were characterized with regard to morphology, size and size distribution, BSA loading efficiency, in vitro BSA release, and BSA stability.

RESULTS

The protein-containing PLGA-PVA composite microspheres possessed spherical shape and nonporous surface. The PLGA-PVA composite microspheres had normal or Gaussian size distribution. The particle size ranged from 71.5 microm to 282.7 microm. The average diameter of the composite microspheres was 180 microm. The PLGA-PVA composite microspheres could release the protein (BSA) for two months. The protein stability study showed that BSA was protected during the composite microsphere preparation and stabilized inside the PLGA-PVA composite microspheres.

CONCLUSIONS

The protein-containing PLGA-PVA composite may be suitable for long-term protein drug delivery.

Gamma irradiation for terminal sterilization of 17beta-estradiol loaded poly-(D,L-lactide-co-glycolide) microparticles

17beta-Estradiol-loaded microparticles using poly-(D, L-lactide-co-glycolide) polymer (PLG) were prepared by a modified spray-drying method and the effects of gamma-irradiation on drug substance, polymer and microparticles were investigated. Irradiation doses ranging from 5.1 to 26.6 kGy were applied using a 60Co-radiation source. 17beta-Estradiol drug substance showed excellent stability against gamma-irradiation in the investigated dose range, whereas microencapsulated estradiol seems to be converted to conjugation products with PLG, and to a lesser extent to the degradation product 9,11-dehydroestradiol. The weight-average molecular weight of the PLG polymers decreased with increasing irradiation dose while polydispersity indices (M(w)/M(n)) remained nearly unchanged, compatible with a random chain scission mechanism in lactide/glycolide-copolymer degradation. In vitro drug release studies showed accelerated kinetics with increasing irradiation doses due to dose dependent polymer degradation. Microbiological process monitoring showed decreasing bioburden with increasing spraying time, which was successfully further reduced by applying irradiation sterilization. Microencapsulated test spore suspensions of Bacillus pumilus ATCC 27142, the official test specimen for the gamma-sterilization process, revealed effective reduction of bioburden, confirming its published D(10) value. In conclusion, our studies demonstrated efficacy of gamma-irradiation as terminal sterilization method for poly-(D,L-lactide-co-glycolide) polymer-based drug delivery systems. The sterilization conditions need to be carefully adjusted for the final dosage form.

Mechanism of drug release from poly(L-lactic acid) matrix containing acidic or neutral drugs

The release profiles of acidic and neutral drugs from poly(L-lactic acid) [P(L)LA] matrices were investigated to reveal their release mechanism. Cylindrical matrices (rods; 10 mmx1 mm diameter) were prepared by the heat compression method. The acidic and neutral drugs investigated were dissolved in the P(L)LA rods. It was found that the release profiles consisted of two sequential stages. At the first release stage, P(L)LA remained in an amorphous state and the drugs diffused through the hydrated matrices. At the second release stage, P(L)LA transformed to a semicrystalline state and the drugs diffused through water-filled micropores developed by polymer crystallization. In addition, the drugs were also found to precipitate out as crystals in the rods, resulting in a transformation of the rods into drug-dispersed matrices. On the basis of these findings, we derived a modified diffusion equation for the drug release at the second stage. This equation showed good fits to the release profiles of these drugs. Furthermore, the availability of the derived equation was supported by the acceleration in the fractional drug release rate noted both with decreases in the drug content in the rod and increases in the pH of the medium.

Vaccine delivery to animals

For many years vaccination of animals has been practiced to prevent infectious diseases using inactivated organisms or modified live organisms. The live vaccines were effective but lacked safety. The vaccines made with inactivated organisms required an adjuvant to induce an immune response that was not as effective as either the clinical disease or live vaccines. An 'ideal' vaccine would induce effective immunity specific for the type of infection, have long duration, require minimal or no boosters, have impeccable safety, would not induce adverse reactions, and be easy to administer. The desire to meet these criteria, and especially safety, has resulted in the development of vaccines that do not depend on the use of the viable disease agent. The emphasis on subunit or inactivated vaccines that meet the desired criteria of a perfect vaccine has resulted in a critical need for better adjuvants and delivery systems. This has resulted in a technological innovation revolution with development of a wide array of different technologies to generate effective vaccines. This review will describe the historical relevance of adjuvants used for parenterally administered inactivated/subunit vaccines as well as describe some of the exciting technological advances including adjuvants (ISCOMS), delivery systems (recombinant vectors, microparticles), and novel approaches (transgenic plants, naked DNA) that are currently being, or will be used in the future, in the search for better, more effective vaccines that meet the current and future needs of veterinary medicine.

A new stabilizer used in microencapsulation

In this communication, a new microencapsulation method is reported to entrap solid drug powder in an aqueous system. A hydrophobically modified, random polyacrylamide derivative was used as a stabilizer: with a hydrophilic back bone and hydrophobic side chain, it showed good dispersing and stabilizing effects in the preparation of microcapsules. The preparation of streptomycin microcapsules, using poly(lactide) and poly(caprolactone), showed the successful entrapment of streptomycin powder which is readily soluble in water (solubility larger than 20 mg/ml). In addition, a low concentration of stabilizer (0.25%) is used and a short preparation process is also an advantage of the method.

Nonparametric analysis of the absorption profile of octreotide in rabbits from long-acting release formulation OncoLAR

Octreotide (octreotide-acetate, Sandostatin(R)) is a somatostatin analogue, used in long-term treatment of acromegaly. The present study describes the absorption profile in rabbits of octreotide after release from the long-acting formulation OncoLAR (denoted as octreotide-LAR). In a first experiment, the disposition kinetics of octreotide was studied for 24 h in six rabbits after intravenous (i. v.) injection of 0.025 mg of a solution of octreotide. In a second experiment, release kinetics was studied in eight rabbits for 49 days after an i.m. injection of 5 mg/kg of octreotide-LAR. Concentrations were determined by radioimmunoassay. After i.v. injection of octreotide, one- and two-compartment models were compared for each rabbit. A typical disposition profile was computed using the mean parameters. After i.m. injection of octreotide-LAR, deconvolution was performed using the point-area method. Individual absorption profiles were characterised using natural splines. The number of breakpoints was selected using the generalised cross-validation criterion. The two compartment model was selected based on the i.v. study. After i.m. administration, octreotide exhibited a triphasic absorption profile, with large interindividual variability. A transient peak followed the initial burst phase. The third phase covered 85% of total drug released. The approach allows a model-independent description of the in vivo absorption profile of octreotide-LAR.

Tetracycline-HCl-loaded poly(DL-lactide-co-glycolide) microspheres prepared by a spray drying technique: influence of gamma-irradiation on radical formation and polymer degradation

Tetracycline-HCl (TCH)-loaded microspheres were prepared from poly(lactide-co-glycolide) (PLGA) by spray drying. The drug was incorporated in the polymer matrix either in solid state or as w/o emulsion. The spin probe 4-hydroxy-2,2,6, 6-tetramethyl-piperidine-1-oxyl (TEMPOL) and the spin trap tert-butyl-phenyl-nitrone (PBN) were co-encapsulated into the TCH-loaded and placebo particles. We investigated the effects of gamma-irradiation on the formation of free radicals in polymer and drug and the mechanism of chain scission after sterilization. Gamma-Irradiation was performed at 26.9 and 54.9 kGy using a 60Co source. The microspheres were characterized especially with respect to the formation of radicals and in vitro polymer degradation. Electron paramagnetic resonance (EPR) spectroscopy, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), high-performance liquid chromatography (HPLC), gas chromatography-mass spectroscopy (GC-MS), and scanning electron microscopy (SEM) were used for characterization of the microspheres. Using EPR spectroscopy, we successfully detected gamma-irradiation induced free radicals within the TCH-loaded microspheres, while unloaded PLGA did not contain radicals under the same conditions. The relatively low glass transition temperature of the poly(dl-lactide-co-glycolide) (37-39 degrees C) seems to favor subsequent reactions of free radicals due to the high mobility of the polymeric chains. Because of the high melting point of TCH (214 degrees C), the radicals can only be stabilized in drug loaded microspheres. In order to determine the mechanism of polymer degradation after exposure to gamma-rays, the spin trap PBN and the spin probe TEMPOL were encapsulated in the microspheres. gamma-Irradiation of microspheres containing PBN resulted in the formation of a lipophilic spin adduct, indicating that a polymeric radical was generated by random chain scission. Polymer degradation by an unzipping mechanism would have produced hydrophilic spin adducts of PBN and monomeric radicals of lactic or glycolic acid. These degradation products were not detected by EPR. This result is confirmed by the observation that possible diamagnetic reaction products of low molecular weight, consisting of TEMPOL and lactide or glycolide monomers, could not be detected by GC-MS. While an irradiation dose-dependent decrease in molecular weight of PLGA could be verified in agreement with the literature, TCH content of the microspheres was not affected by the exposure to gamma-rays. It can be concluded that EPR spectroscopy in combination with GPC, DSC, and HPLC allows a detailed characterization of the impact of gamma-sterilization on biodegradable parenteral drug delivery systems.

Preparation of non-porous microspheres with high entrapment efficiency of proteins by a (water-in-oil)-in-oil emulsion technique

Emulsification-solvent removal methods have been widely used for encapsulating bioactive macromolecules like proteins and polypeptides in biodegradable polymers. We report, a (water-in-oil)-in-oil emulsion technique wherein proteins and polypeptides differing in molecular weight and shape were encapsulated in polymers of current biomedical interest. When an oil was used as the processing medium in combination with a carefully selected mixed solvent system such that a stable (w/o1/o2 emulsion is formed and solvents are removed by a combination of extraction and evaporation, the entrapment efficiency was high and the product nonporous. The entrapment efficiency of globular proteins exceeded 90% while that of fibrous proteins was around 70%. Fracture studies revealed that the polymer matrix was dense. The mechanism of entrapment involved solvent-induced precipitation of the protein as the microspheres were being formed. The principle of the method will find use in preparation of non-porous polymer microparticles with reduced burst effect.

Factors influencing the diffusion-controlled release of papaverine from poly (L-lactic acid) matrix

Effects of drug content and medium pH on the release of papaverine (PAP) from biodegradable poly(l-lactic acid) [P(L)LA] matrix were investigated to reveal the predominant factors affecting the two-stage diffusion-controlled release mechanism. A drug-dissolved cylindrical matrix (rod; 10 mmx1 mm diameter) was prepared by heat compression method. In the case of a PAP content below 10%, pH was found to have a strong effect on the release rate, and drug content was found to have no effect on the release profile. The release profile consisted of two sequential diffusion stages due to P(L)LA transformation from amorphous to the semicrystalline state prior to release. In the first release stage PAP diffused through the swollen matrix. The release accelerated with increasing medium pH due to an increase in water content in the acidic P(L)LA rod. In the second release stage PAP diffused through the water-filled micropores developed as a result of the polymer crystallization. On the assumption that the drug partition between the polymer and the medium in the micropores affects the diffusion and the partition is controlled by pH, we derived a modified diffusion kinetic equation. The observation that the release decelerated with increasing medium pH can be explained by the derived equation as resulting from the increase in the drug partition to the polymer. In the case where the rods contained more than 15% of PAP, the drug precipitated out as crystals during release. Accordingly, these rods showed a slower release.

Controlled drug delivery by biodegradable poly(ester) devices: different preparative approaches

There has been extensive research on drug delivery by biodegradable polymeric devices since bioresorbable surgical sutures entered the market two decades ago. Among the different classes of biodegradable polymers, the thermoplastic aliphatic poly(esters) such as poly(lactide) (PLA), poly(glycolide) (PGA), and especially the copolymer of lactide and glycolide referred to as poly(lactide-co-glycolide) (PLGA) have generated tremendous interest because of their excellent biocompatibility, biodegradability, and mechanical strength. They are easy to formulate into various devices for carrying a variety of drug classes such as vaccines, peptides, proteins, and micromolecules. Most importantly, they have been approved by the United States Food and Drug Administration (FDA) for drug delivery. This review presents different preparation techniques of various drug-loaded PLGA devices, with special emphasis on preparing microparticles. Certain issues about other related biodegradable polyesters are discussed.

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.

Subcutaneous administration of a depot gonadotropin-releasing hormone agonist induces profound reproductive axis suppression in women

OBJECTIVE

To compare the i.m. and s.c. routes of depot GnRH agonist administration.

DESIGN

Prospective, controlled pharmacokinetics study.

SETTING

Volunteers in an academic research environment.

PATIENT(S)

Forty women with benign gynecologic disorders.

INTERVENTION(S)

Triptorelin administration (3.75 mg) at 28-day intervals for 6 consecutive months. Twenty patients were treated with IM triptorelin, and 20 patients were treated with SC triptorelin.

MAIN OUTCOME MEASURE(S)

Assessment of side effects, GnRH test results, and triptorelin, LH, FSH, estradiol, and progesterone levels.

RESULT(S)

The occurrence of injection site redness and itching and of some hypoestrogenic side effects was increased significantly in the SC group. Plasma triptorelin levels were significantly higher in the IM group in the first month of treatment; thereafter, the pattern reversed, with a nonsignificant trend toward higher plasma triptorelin levels in the SC group. Serum LH, FSH, estradiol, and progesterone levels were low after the first month of treatment and did not differ between the two treatment groups. On day 196 (2 months after the last depot triptorelin injection), triptorelin was still measurable and gonadotropins and gonadal steroids were still suppressed. Spontaneous menses returned significantly later in the SC group than in the IM group.

CONCLUSION(S)

Subcutaneous triptorelin can be administered by the patient. Both IM and SC triptorelin administration are cliniclly effective, but they result in different triptorelin pharmacokinetics. Subcutaneous triptorelin is associated with more prolonged amenorrhea than is IM triptorelin, suggesting enhanced pituitary-ovarian suppression. These results suggest that SC triptorelin may allow lower drug dosage administration and/or longer administration intervals.

Drug microencapsulation by PLA/PLGA coacervation in the light of thermodynamics. 2. Parameters determining microsphere formation

Phase separation (frequently called coacervation) of poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) is a classical method for drug microencapsulation. Here, attempts have been made to describe this process in the light of thermodynamics. Different PLA/PLGAs were dissolved in either dichloromethane or ethyl acetate, phase separated by addition of the coacervating agent silicone oil (PDMS), and hardened in either octamethylcyclotetrasiloxane or hexane. Various stages of phase separation were defined microscopically, and the coacervate and continuous phases characterized with respect to volume, composition, polymer molecular weight, and rheological behavior. The optimal amount of PDMS was inversely proportional to the polymer molecular weight and hydrophilicity, and a coacervate viscosity of above 5-10 Pa s was required for stable coacervate droplets. The composition and, consequently, viscosity of the coacervate and continuous phases depended on the polymer-solvent-PDMS interactions, as analyzed by the parameters chi (Flory), delta (Hildebrand), and delta(int)E (Hô). In general, the lattice model of FIory and Scott describing polymer-polymer incompatibility best explained the results. The interaction parameters and viscosity of the phases were also helpful to explain microsphere characteristics such as residual solvent and particle size. The data suggest that microsphere formation by polyester coacervation is primarily driven by molecular interactions between polymer, solvents, and coacervating agent.

Drug microencapsulation by PLA/PLGA coacervation in the light of thermodynamics. 1. Overview and theoretical considerations

Phase separation of poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA), often called "coacervation" in the pharmaceutical field, is one of the classical methods for peptide drug microencapsulation in biodegradable polyesters. Although numerous studies have used this technique, the underlying physicochemical mechanisms of polyester coacervation under conditions of microsphere production have not been well-described yet. Moreover, the quality of microencapsulation in terms of drug loading efficiency and residual organic solvents is often not entirely satisfactory and depends greatly on the specific drug and polymer used. The first part of this contribution reviews briefly the scientific and patent literature on PLA/PLGA coacervation. Then, the underlying physicochemical principles of polyester coacervation are discussed and relevant thermodynamic models presented. More specifically, attempts were made to clarify the necessary characteristics of polymers, solvents, and coacervating and hardening agents for successful phase separation and microsphere formation. These basic considerations may contribute to a better understanding of the boundary conditions crucial for efficient drug microencapsulation by polyester coacervation.

One- and three-month release injectable microspheres of the LH-RH superagonist leuprorelin acetate

The biodegradable polymers poly(lactic/glycolic acid) (PLGA) and poly(lactic acid) (PLA) were used as wall materials in the preparation of microspheres (msp) containing the LH-RH superagonist leuprorelin (leuprolide) acetate. A novel W/O/W emulsion-solvent evaporation method was devised for the preparation of msp containing this water-soluble peptide. This method achieved high entrapment efficiency and sustained drug release over a long period predominantly due to polymer bioerosion. The msp are fine microcapsules with polycores containing the peptide at a high concentration and are easily injectable through a conventional fine needle. Leuprorelin msp made with PLGA(75/25)-14,000 or PLA-15,000 released the drug in a zero-order fashion, maintained constant serum drug levels and attained persistent objective suppression of the pituitary-gonadal system ('chemical castration') over 1 or 3 months after i.m. or s.c. injection into animals. These results indicate that depot formulations may be potentially useful in the therapy of endocrine diseases in humans. In this paper, studies on the formulation, drug release and pharmacological effects in animals for these leuprorelin depot formulations are reviewed.

Utilization of an amorphous form of a water-soluble GPIIb/IIIa antagonist for controlled release from biodegradable microspheres

PURPOSE

We prepared injectable microspheres for controlled release of TAK-029, a water-soluble GPIIb/IIIa antagonist and discussed the characteristics of controlled release from microspheres.

METHODS

Copoly(dl-lactic/glycolic)acid (PLGA) microspheres were used for controlled release of TAK-029 [4-(4-amidinobenzoylglycyl)-3-methoxycarbonyl-2-oxopiperazine++ +-1-acetic acid]. They were prepared with a solid-in-oil-in-water (S/O/W) emulsion solvent evaporation technique using either a crystalline form or an amorphous form of the drug.

RESULTS

An amorphous form of TAK-029 gave more homogeneous S/O dispersion and higher viscosity than its crystalline form when added to dichloromethane solution of PLGA, resulting in a high drug entrapment into microspheres and a well-controlled release of the drug. Additions of sodium chloride into an external aqueous phase and L-arginine into an oil phase also increased entrapment of the drug, and reduced initial burst of the drug from the microspheres. The microspheres demonstrated a desirable plasma level profile in therapeutic range (20-100 ng/ml) for 3 weeks in rats after single subcutaneous injection.

CONCLUSIONS

A well-controlled release of TAK-029, a water-soluble neutral drug, with small initial burst was achieved by utilizing its amorphous form as a result of possible interaction with PLGA and L-arginine.

Improved activity of a new angiotensin receptor antagonist by an injectable spray-dried polymer microsphere preparation

PURPOSE

To characterize and evaluate in vitro and in vivo the release mechanisms involved in spray-dried biodegradable microspheres having different Poly(D,L-lactide) blend formulations and containing an antihypertensive drug (L-158,809).

METHODS

Microspheres and blended polymers were characterized by DSC, SEM, confocal laser microscopy and size analysis. In vitro release studies were evaluated by using microspheres made from various blends of high and low molecular weight polymer. In vivo studies were evaluated by L-158,809 antagonist AT1 function versus the shift of the normal dose-response curve of blood pressure induced by Angiotensine II.

RESULTS

The average yield of L-158,809 microspheres (10% (w/w)) was 95% of the theoretical loading. The average diameter of the microspheres was from 1 to 3 micrometers. In all release experiments, a significant burst effect (< 15%) was observed followed by a near zero-order release kinetics. In vivo studies with two different formulations show a strong shift of angiotensin II dose-response curve.

CONCLUSIONS

The release kinetics and photomicrographs suggest that the system is best described as a multi-parameter controlled released system in which the drug is molecularly dispersed. In vivo results demonstrating the controlled release of L-158,809.

In vitro characterization of methotrexate loaded poly(lactic-co-glycolic) acid microspheres and antitumor efficacy in Sarcoma-180 mice bearing tumor

Methotrexate (MTX) loaded poly (lactic-co-glycolic) acid (PLGA) microspheres were prepared by emulsion solvent evaporation technique. The mean diameter of the microspheres was affected by the type of emulsion stabilizer, polymer concentration, aqueous and organic phase volume and stirring speed. The in vitro release was triphasic and was dependent on copolymer composition and molecular weight of the polymer. Antitumor efficacy in Sarcoma-180 tumor bearing mice exhibited increased volume doubling time (18 +/- 2.7 days) compared to plain subcutaneous injection of methotrexate (8 +/- 0.7 days). Preliminary pharmacokinetic studies following subcutaneous administration of MTX loaded PLGA microspheres illustrated the controlled release of the drug. The studies demonstrated the feasibility of employing PLGA as an effective carrier for antineoplastic drug like methotrexate.