Understanding and Predicting Drug Delivery from Hydrophilic Matrix Tablets Using the “Sequential Layer” Model

Purpose. The objectives of this work were (i) to study and understand the physicochemical phenomena which are involved in the swelling and drug release from hydrophilic matrix tablets using the sequential layer model; and (ii) to predict the effect of the initial radius, height and size of the tablets on the resulting drug release profiles. Methods. Tablets were prepared by direct compression, using hydroxypropyl methylcellulose (HPMC) grades with different average molecular weights as matrix-forming polymers. The in vitro release of chlorpheniramine maleate, propranolol HCl, acetaminophen, theophylline and diclofenac sodium was studied in phosphate buffer (pH 7.4) and 0.1 M HCl, respectively. The initial drug loading varied from 1 to 70%, while the radius and height of the tablets varied from 1 to 8 mm. Results. The sequential layer model considers water and drug diffusion with non-constant diffusivities and moving boundary conditions, non-homogeneous polymer swelling, drug dissolution, and polymer dissolution. We showed that this model was able to predict the resulting drug release kinetics accurately in all cases. Conclusions. The sequential layer model can be used to elucidate the swelling and drug release behavior from hydrophilic matrix tablets and to simulate the effect of the device geometry on the drug release patterns. Hence, it can facilitate the development of new pharmaceutical products.     

pH-Triggered Release of Macromolecules from Spray-Dried Polymethacrylate Microparticles

Purpose. pH-triggered microparticles release their therapeutic payloads at acidic pH (e.g., in the phagosome), making intracellular drug delivery more efficient. Here we modify lipid-based microparticles that are safe and efficacious in nerve and brain and are potentially inhalable, making them pH-triggerable by incorporating an acid-soluble polymethacrylate, Eudragit E100 (E100). Methods. Microparticles were produced by spray-drying and characterized by electron microscopy, Coulter counting, density measurement, and release kinetics of fluorescently labeled proteins. In addition, biocompatibility and cellular uptake were observed in rats. Results. Microparticles were spheroids 3 to 5 m in diameter with densities of 0.12 to 0.25 g/L. Microparticles with 20% (w/w) or more E100 demonstrated slow release of fluorescently labeled proteins at pH 7.4 but rapid release at pH 5. pH-triggerability was maintained for over 2 weeks in solution. Protein loadings of 0.2-20% (w/w) were pH-triggerable. Histologic examination of particles in rat connective tissue near nerve and muscle demonstrated biocompatibility aside from muscle edema in the cell layers adjacent to the particles and a localized inflammatory reaction with macrophages laden with microparticles. Conclusions. Microparticles containing E100 were pH-triggerable for many days and were taken up by macrophages, suggesting that they may be useful for intracellular drug delivery.     

Inhalable Microparticles Containing Drug Combinations to Target Alveolar Macrophages for Treatment of Pulmonary Tuberculosis

Purpose: Drug therapy of tuberculosis (TB) requires long-term oral administration of multiple drugs for curing as well as preventing and/or combating multi-drug resistance. Persistent, high blood levels of antitubercular drugs resulting from prolonged oral administration of anti-TB drugs may be neither necessary nor sufficient to kill mycobacteria residing in macrophages (M). Inhalable biodegradable microparticles containing two of the first-line anti-TB drugs, isoniazid (H), and rifampicin (R), were prepared and tested for (i) phagocytosis by mouse M, (ii) administration as a dry powder inhalation to rats, and (iii) targeting alveolar M with high drug doses when administered to rats. Methods: poly(D-L lactic acid) microparticles were prepared by emulsion methods and their drug content and size distribution determined. These were tested for uptake by murine M in culture and resultant intracellular drug concentrations determined by high performance thin-layer chromatography (HPTLC). Rats were administered an inhalation of microparticles using an inhalation chamber developed in the lab. The extent of microparticle delivery in vivo was examined by flow-cytometry. Drug concentrations in the blood and in alveolar M were estimated by high-performance liquid chromatography after oral, vascular, intratracheal, and inhalation administration. Results: Inhalable microparticles could be prepared and were taken up by cultured M. Large numbers of particles could be delivered to the bronchiopulmonary system through a 2-min exposure to fluidized particles. The intracellular drug concentrations resulting from vascular delivery of soluble drugs were found to be lower than those resulting from particle inhalation. Conclusions: Inhalable microparticles containing multiple anti-TB drugs offer promises of dose and dosing-frequency reduction, toxicity alleviation, and targeting M-resident persistent mycobacteria.     

Analysis of the Initial Burst of Drug Release Coupled with Polymer Surface Degradation

Purpose. Local pH effect on the release of a model pH-inert hydrophobic drug coupled with polymer degradation is described at the induction phase of biodegradable polymer erosion for better understanding the nature of initial burst of a drug. Methods. Using a novel approach with time-of-flight secondary ion mass spectrometry, both surface concentration of Ph₃N and degradation kinetics of PLLA are simultaneously and independently determined from a model Ph₃N/PLLA (20:80 wt%) blend matrix (t 0.4 m on 1.0 cm²). In vitro hydrolysis of the model blend matrix is investigated for short-term periods (<24 h) at physiologic pH and temperature and compared to basic pH. Results. The rate of PLLA degradation is accelerated by a factor of 3 when using basic pH in vitro, but the rate of Ph₃N accumulation at the surface is accelerated by a factor of 6. Conclusions. A new quantitative method has been developed to examine the earliest stages of polymer degradation and drug release. It was applied to a model system that could not be examined by traditional in vitro methods. For the model system studied the release of a low molecular weight hydrophobic drug at the induction phase of polymer erosion is related to but not singularly dependent on degradation kinetics.     

The Mechanism of Uptake of Biodegradable Microparticles in Caco-2 Cells Is Size Dependent

Purpose. To study the uptake of biodegradable microparticles in Caco-2 cells. Methods. Biodegradable microparticles of polylactic polyglycolic acid co-polymer (PLGA 50:50) of mean diameters 0.1 m, 1 m, and 10 m containing bovine serum albumin as a model protein and 6-coumarin as a fluorescent marker were formulated by a multiple emulsion technique. The Caco-2 cell monolayers were incubated with each diameter microparticles (100 g/ml) for two hours. The microparticle uptake in Caco-2 cells was studied by confocal microscopy and also by quantitating the 6-coumarin content of the microparticles taken up by the cells. The effects of microparticle concentration, and incubation time and temperature on microparticle cell uptake were also studied. Results. The study demonstrated that the Caco-2 cell microparticle uptake significantly depends upon the microparticle diameter. The 0.1 m diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 m and 6 fold greater than the 10 m diameter microparticles. Similarly in terms of number the uptake of 0.1 m diameter microparticles was 2.7 × 10³ fold greater than the 1 m and 6.7 × 10⁶ greater than the 10 m diameter microparticles. The efficiency of uptake of 0.1 m diameter microparticles at 100 g/ml concentration was 41% compared to 15% and 6% for the 1 m and the 10 m diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 m) uptake increased with concentration in the range of 100 g/ml to 500 g/ml which then reached a plateau at higher concentration. The uptake of microparticles increased with incubation time, reaching a steady state at two hours. The uptake was greater at an incubation temperature of 37°C compared to at 4°C. Conclusions. The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 m) had significantly greater uptake compared to larger diameter microparticles. The results thus suggest that the mechanism of uptake of microparticles in Caco-2 cell is particle diameter dependent. Caco-2 cells are used as an in vitro model for gastrointestinal uptake, and therefore the results obtained in these studies could be of significant importance in optimizing the microparticle-based oral drug delivery systems.     

Preparation and in Vitro/in Vivo Evaluation of Insulin-Loaded Poly(Acryloyl-Hydroxyethyl Starch)-PLGA Composite Microspheres

Purpose. The purpose of this study was to develop and evaluate a novel composite microsphere delivery system composed of poly(D,L-lactide-co-glycolide) (PLGA) and poly(acryloyl hydroxyethyl starch) (acryloyl derivatized HES; AcHES) hydrogel using bovine insulin as a model therapeutic protein. Methods. Insulin was incorporated into the AcHES hydrogel microparticles by a swelling technique, and then the insulin-containing AcHES microparticles were encapsulated in a PLGA matrix using a solvent extraction/evaporation method. The composite microspheres were characterized for loading efficiency, particle size, and in vitro protein release. Protein stability was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis, high-performance liquid chromatography, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The hydrogel dispersion process was optimized to reduce the burst effect of microspheres and avoid hypoglycemic shock in the animal studies in which the serum glucose and insulin levels as well as animal body weight were monitored using a diabetic animal model. Results. Both the drug incorporation efficiency and the in vitro release profiles were found to depend upon the preparation conditions. Sonication effectively dispersed the hydrogel particles in the PLGA polymer solution, and the higher energy resulted in microspheres with a lower burst and sustained in vitro release. Average size of the microspheres was around 22 m and the size distribution was not influenced by sonication level. High-performance liquid chromatography, sodium dodecyl sulfate polyacrylamide gel electrophoresis, along with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry showed the retention of insulin stability in the microspheres. Subcutaneous administration of microspheres provided glucose suppression <200 mg/dL for 810 days with hyperglycemia recurring by day 16. During the treatment, the time points with higher serum insulin level were consistent with a more significant glucose suppression. The microsphere-treated rats also grew virtually at the same rate as normal control until the insulin level declined and hyperglycemia returned. Multiple dosing given every 10 days demonstrated that the pharmacological effect and serum insulin levels from second or third doses were similar and comparable to that of the first dose. Conclusion. The AcHES-PLGA composite microsphere system provides satisfactory in vitro and in vivo sustained release performance for a model protein, insulin, to achieve 10-day glucose suppression.     

Pharmaceutical Evaluation of Gas-Filled Microparticles as Gene Delivery System

Purpose. To produce and characterize a nonviral ultrasound-controlled release system of plasmid DNA (pDNA) encapsulated in gas-filled poly(D,L-lactide-co-glycolide) microparticles (PLGA-MPs). Methods. Different cationic polymers were used to form pDNA/polymer complexes to enhance the stability of pDNA during microparticle preparation. The physico-acoustical properties of the microparticles, particle size, pDNA integrity, encapsulation efficiency and pDNA release behavior were studied in vitro. Results. The microparticles had an average particle size of around 5 m. More than 50% of all microparticles contained a gas core, and when exposed to pulsed ultrasound as used for color Doppler imaging create a signal that yields typical color patterns (stimulated acoustic emission) as a result of the ultrasound-induced destruction of the microparticles. Thirty percent of the pDNA used was successfully encapsulated and approximately 10% of the encapsulated pDNA was released by ultrasound within 10 min. Conclusions. Plasmid DNA can be encapsulated in biodegradable gas-filled PLGA-MPs without hints for a structural disintegration. A pDNA release by ultrasound-induced microparticle-destruction could be shown in vitro.     

In Vitro Evaluation of Microparticles and Polymer Gels for Use as Nasal Platforms for Protein Delivery

Purpose. Nasal delivery of protein therapeutics can be compromised by the brief residence time at this mucosal surface. Some bioadhesive polymers have been suggested to extend residence time and improve protein uptake across the nasal mucosa. We examined several potential polymer platforms for their in vitro protein release, relative bioadhesive properties and induction of cytokine release from respiratory epithelium. Methods. Starch, alginate, chitosan or Carbopol^® microparticles, containing the test protein bovine serum albumin (BSA), were prepared by spray-drying and characterized by laser diffraction and scanning electron microscopy. An open-membrane system was used to determine protein release profiles and confluent, polarized Calu-3 cell sheets were used to evaluate relative bioadhesion, enhancement of protein transport and induction of cytokine release in vitro. Results. All spray-dried microparticles averaged 2–4 m in diameter. Loaded BSA was not covalently aggregated or degraded. Starch and alginate microparticles released protein more rapidly but were less adhesive to polarized Calu-3 cells than chitosan and Carbopol^® microparticles. Protein transport across polarized Calu-3 cells was enhanced from Carbopol^® gels and chitosan microparticles. A mixture of chitosan microparticles with lysophosphatidylcholine increased protein transport further. Microparticles prepared from either chitosan or starch microparticles, applied apically, induced the basolateral release of IL-6 and IL-8 from polarized Calu-3 cells. Release of other cytokines, such as IL-l, TNF-, GM-CSF and TGF-, were not affected by an apical exposure to polymer formulations. Conclusions. We have described two systems for the in vitro assessment of potential nasal platforms for protein delivery. Based upon these assessments, Carbopol^® gels and chitosan microparticles provided the most desirable characteristics for protein therapeutic and protein antigen delivery, respectively, of the formulations examined.     

Preparation and evaluation of double-walled microparticles prepared with a modified water-in-oil-in-oil-in-water (w1/o/o/w3) method

Abstract

In this study, a modified water-in-oil-in-oil-in-water (w₁/o/o/w₃) method was developed to prepare double-walled microparticles containing ovalbumin (OVA). The microparticles were characterized with respect to their morphology, particle size, encapsulation efficiency, production yield, thermal properties and in vitro drug release. Microscopy observations clearly showed that microparticles have spherical shape and smooth surface. These microparticles were characterized to have double-walled structure, with a cavity in the centre. By using w₁/o/o/w₃ method, a significant decrease in mean particle size and a significant increase in encapsulation efficiency were obtained. The mean particle size and the encapsulation efficiency of double-walled microparticles were also affected by the changing amount of OVA and mass ratio of polymers. Microparticles prepared with two polymers exhibited a significantly lower initial burst release followed by sustained release compared to microparticles made from poly(d,l-lactide-co-glycolide) 50/50 only. It can be concluded that these microparticles can be a potential delivery system for therapeutic proteins.     

PLG Microsphere Size Controls Drug Release Rate Through Several Competing Factors

Purpose. Although the rate of drug release from poly(D,L-lactide-co-glycolide) (PLG) microspheres is often modulated by changing fabrication conditions or materials, the specific factors directly controlling the release profiles are often unclear. We have fabricated uniform rhodamine- and piroxicam-containing microspheres, 10 to 100 m in diameter, to better understand how microsphere size controls drug release. Methods. Drug distribution within the microspheres was examined using confocal fluorescence microscopy. The rate of polymer degradation was determined as the change in molecular weight, measured by gel permeation chromatography, during in vitro degradation experiments. Further, changes in the surface and interior morphology of the particles during in vitro degradation were investigated by scanning electron microscopy. Results. Microsphere size greatly affected drug distribution. Small (10-m) microspheres showed an essentially uniform drug distribution. Larger (100-m) microspheres showed redistribution of drug to specific regions of the microspheres. Rhodamine partitioned to the surface and piroxicam partitioned to the interior of large PLG microspheres. Further, the rate of polymer degradation increased with microsphere size, possibly the result of a more acidic interior caused by increased accumulation of hydrolyzed polymer products in larger particles. Finally, larger microspheres developed a more porous interior structure during the drug release. Conclusions. Microsphere size affects drug release not only through changes in diffusion rates but also through secondary effects including drug distribution in the particle, polymer degradation rate, and microsphere erosion rates.     

Preparation of Biodegradable Microparticles Using Solution-Enhanced Dispersion by Supercritical Fluids (SEDS)

Purpose. We have evaluated a new process, involving solution-enhanced dispersion by supercritical fluids (SEDS), for the production of polymeric microparticles. Methods. The biodegradable polymers, Poly (DL-lactide-co-glycolide) : copolymer composition 50:50 (DL-PLG), Poly (L-lactide) (L-PLA), Poly (DL-lactide) (DL-PLA) and Polycaprolactone (PCL), were used for preparation of microparticles using SEDS. Solutions of the polymers in organic solvents were dispersed and sprayed with supercritical CO₂. Extraction of the organic solvents resulted in the formation of solid microparticles. The amounts of highly toxic solvents such as dichloromethane (MC) were reduced in the process. Results. Microparticles were obtained from all polymers. The mean particle size and shape varied with the polymer used. The morphology of the particles was strongly affected by the choice of polymer solvent. Discrete spherical microparticles of DL-PLG were produced with a mean volumetric diameter of 130 m. The microparticles of the L-PLA were almost spherical, and their size increased from 0.5 to 5 m as the density of supercritical CO₂ decreased. PCL formed microparticles with diameters of 30–210 m and showed a strong tendency to form films at high pressure. Conclusions. The SEDS process appears a promising method for production of microparticles from biodegradable polymers without the use of toxic solvents.     

Formation of Multilayers in the Caco-2 Cell Culture Model: A Confocal Laser Scanning Microscopy Study

Purpose. To introduce confocal laser scanning microscopy (CLSM)combined with digital image restoration to characterise Caco-2 cellsunder different culture conditions, and thus to define additional validcriteria for the optimisation of culture models. Methods. Growth curves were established and transepithelial electricalresistance (TEER) measured for cells grown in EMEM or DMEMmedium on Cyclopore membranes. Cytoskeleton, cell nuclei and tightjunctions (TJ) were investigated by CLSM. Results. Cultures reached a plateau of 4.5 × 10⁵ cells/cm² after 10 days. At the same time TEER reached 750 cm². An irregular,fairly complete network of TJ was present at confluence (2 d).Between 15 and 30 days a regular TJ network was established. Cellsformed mixed mono- and multilayers under most conditions with twoexceptions: flat monolayers were observed on polycarbonate filterswith EMEM and with the Biocoat intestinal epithelium differentiationenvironment system. In multilayers TJ were found in the upper aswell as in the lower cell layers although the regular vertical polaritywas disturbed. Conclusions. CLSM represents an important tool to investigate thecytoarchitecture of Caco-2 cells. 3D-analysis of confocal data givesimportant clues on the characteristics of cell layers and thus helps tovalidate optimisation strategies.     

Comparison of the Hanson Microette® and the Van Kel Apparatus for In Vitro Release Testing of Topical Semisolid Formulations

Purpose. The major goal of this study was to compare the relative utility of the Hanson Microette® and the Van Kel apparatus, two fully automated devices, as in vitro release tests (IVRT) for semisolids. We attempted to develop methodology that can be used to discriminate formulation changes, and to evaluate the precision, reproducibility and technical complexity of each test apparatus. Methods. We chose the sunscreen Eusolex®232 (2-Phenylben- zimidazole-5-sulfonic acid) as a model compound, which was incorporated into an emulsion formulation prepared in our laboratory. Test conditions for the two IVRT were made as nearly identical as possible, in order to obtain an accurate comparison. Results. The formulations were tested and found to be physically stable throughout the entire study. Diffusion coefficients were apparatus-dependent but were independent of the drug concentration in the formulations. The IVRT data were plotted as amount released (g/cm²) vs. square root of time (s^0.5) and a linear relationship was obtained in each case. Both methods produced similar results and were able to detect changes in drug loading in the formulations. Conclusions. The linear relationship between the amount released and the square root of time indicates a diffusion-controlled release of drug. Both apparatuses proved to be suitable as tests for formulation sameness according to the FDA's SUPAC-SS guidelines, during level 3 changes. However, each apparatus produced a different release profile for the drug. The choice of apparatus will depend upon a number of considerations.     

Two different biophases for adrenaline released by electrical stimulation or tyramine from the sympathetic nerve endings of the dog saphenous vein

Summary To study the distribution of -and -adrenoceptors dog saphenous vein strips were electrically stimulated (2 ms, 30 V, 0.25–20 Hz). The strips either had spontaneous tone (contraction experiments) or were contracted by 0.28 M prostaglandin F2 in the presence of 7 M phentolamine (relaxation experiments). In strips without preloading or in strips preloaded with (–)-noradrenaline -adrenoceptor-mediated excitatory responses were readily evoked (contraction experiments) but not -adrenoceptor-mediated inhibitory responses (relaxation experiments). In strips preloaded with (–)-adrenaline both -(contraction experiments) and -effects (relaxation experiments) were readily elicited by electrical stimulation and by tyramine. Thus, strips preloaded with (–)-adrenaline were used to compare -with -effects. In these strips the latency between the beginning of the electrical stimulation and the onset of the response was longer for -than for -responses. The same applies to responses to exogenous (–)-adrenaline. However, the ratio latency for -/latency for -response was 3.6±0.2 (n=8) for responses to electrical stimulation and 1.8±0.1 (n=12) for responses to (–)-adrenaline (P<0.001).Cocaine (12M) enhanced the -effect elicited by electrical stimulation 2.8±0.2 (n=7) times but did not change the -effect, whereas U-0521 (50 M) enhanced the -effect 3.4±0.2 (n=8) times without changing the -effect.In strips preloaded with (–)-adrenaline also tyramine caused concentration-dependent -responses (relaxation experiments).The concentration of phentolamine and prazosin required to inhibit contractions caused by electrical stimulation were about 5–7 times higher than those required to inhibit contractions caused by exogenous adrenaline or noradrenaline, whereas propranolol was equipotent in reducing -responses to adrenaline released by electrical stimulation and to exogenous adrenaline. Our results strongly support the view that -adrenoceptors are in close contact with the nerve endings and -adrenoceptors are in close proximity of COMT in a vessel with the nerve endings evenly distributed throughout the media.     

Design and Evaluation of an Osmotic Pump Tablet (OPT) for Chlorpromazine Using (SBE)7m-β-CD

Purpose. The purpose of this study was to develop a controlled-porosity osmotic pump tablet (OPT) which exhibits pH-independent release profiles for a basic drug using a sulfobutyl ether--cyclodextrin, (SBE)_7m--CD, which acts as both a solubilizer and as an osmotic agent. Methods. Chlorpromazine free base (CLP) was chosen as a model drug for this study. The release of CLP from osmotic pump tablets was studied in vitro. In vivo absorption of CLP from the OPT was evaluated in male beagle dogs. Results. The CLP release profile from an OPT prepared from a core tablet composed of a 1:10 molar ratio of CLP to (SBE)_7m--CD was pH-independent, and was controlled by modulating the membrane thickness of the OPT. Another cyclodextrin, hydroxypropyl--cyclodextrin (HP--CD), and a sugar mixture of lactose and fructose resulted in pH-dependent release at the same molar ratio. An in vivo absorption study in dogs with an OPT containing (SBE)_7m--CD correlated very well with the in vitro release profiles using the Japanese Pharmacopoeia dissolution method. Conclusions. In addition to serving as a solubilizer and osmotic agent, (SBE)_7m--CD can also serve as the controlling agent for pH independent release of CLP from OPTs. This system successfully modified the in vivo input rate of CLP without compromising oral bioavailability.     

Design and Evaluation of an Osmotic Pump Tablet (OPT) for Prednisolone,a Poorly Water Soluble Drug,Using (SBE)7m-β-CD

Purpose. The purpose of this study was to develop a controlled-porosity osmotic pump tablet (OPT) for poorly water soluble drugs using a sulfobutyl ether--cyclodextrin, (SBE)_7m--CD or Captisol, which acted as both a solubilizer and as an osmotic agent. Methods. Prednisolone (PDL) was chosen as a model drug for this study. The release of PDL from osmotic pump devices and tablets was studied. In vivo absorption of PDL from OPT was evaluated in male beagle dogs. Results. PDL release from the osmotic pump tablet with (SBE)_7m--CD was complete. Another cyclodextrin, hydroxypropyl--cyclodextrin (HP--CD), and a sugar mixture of lactose and fructose resulted in incomplete release. Although PDL release from the OPT with (SBE)_7m--CD and the sugar formulation displayed mainly zero-order release characteristics, the tablet utilizing HP--CD showed apparent first-order release characteristics. An in vivo absorption study in dogs correlated very well with the in vitro release profiles using the Japanese Pharmacopoeia dissolution method. Conclusions. The present results confirm that (SBE)_7m--CD can serve as both the solubilizer and the osmotic agent for OPT of PDL, and modify the input rate of PDL without compromising oral bioavailability.     

Increased Stabilizing Effects of Amphiphilic Excipients on Freeze-Drying of Lactate Dehydrogenase (LDH) by Dispersion into Sugar Matrices

Purpose. The stabilizing effect of amphiphilic excipients and sugars against protein inactivation during freeze-drying was studied in relation to their physical states in freeze-dried cakes. Methods. Physical states of amphiphilic excipients were studied by powder X-ray diffractometry and differential scanning calorimetry (DSC). Stabilizing effects of excipients were studied using lactate dehydrogenase (LDH) as a model protein. Results. Although poly(ethylene glycols) (PEGs) 1000 to 20000 crystallized when freeze-dried alone, the addition of sugars decreased their crystallinity by dispersing PEG into sugar-dominant matrices. Sugars species, molecular weight of PEGs, and buffer concentration also affected the crystallinity of PEGs. Sugars also dispersed some of other amphiphilic excipients, which tended to crystallize or become microscopically liquid when freeze-dried without sugar. Only the amphiphilic excipients that remained amorphous solid state protected the enzyme during freeze-drying in the absence of sugars. However, combinations of sucrose and all the amphiphilic excipients studied increased the stabilizing effects markedly. The remaining activities were greater than the sum of their individual ones. Conclusions. Various amphiphilic excipients are good stabilizers for freeze-drying of proteins when dispersed into sugar-dominant matrices.     

Biodegradable PLGA Microspheres Loaded with Ganciclovir for Intraocular Administration. Encapsulation Technique,in Vitro Release Profiles,and Sterilization Process

Purpose. The purpose of this work was to obtain a sterilized formulation consisting of biodegradable microspheres of poly (DL-lactide-co-glycolide) (PLGA) for intraocular sustained release of ganciclovir. Methods. Microspheres were prepared using a dispersion of ganciclovir in fluorosilicone oil (FSiO) that was further dispersed in an acetone solution of PLGA [50/50 and inherent viscosity 0.41 dl/g], and emulsified in silicone oil with a surfactant. Once prepared, the formulation was exposed with an effective radiation dose of 2.5 megarads. The release rate data of ganciclovir from the sterilized and nonsterilized batches were compared using the similarity factor (f₂). Results. The dispersion of the drug in FSiO contributed to achieving a drug payload of up to 95% of the theoretical in the 300-500 m microspheres. Ten mg released ganciclovir in vitroat 1.3 g/h for the first 21 days, but decreased to 0.2 g/h from day 25 until the end of the release study (42 days). No significant differences in the amounts of encapsulated drug (=0.05) were observed between the sterilized and nonsterilized microspheres. Furthermore, dissolution profiles of formulations behaved similarly before and after gamma radiation exposure. Conclusions. The technique of microsphere preparation described resulted in high ganciclovir loading (95%) and prolonged drug release. The ganciclovir formulation behaved similarly before and after the sterilization process.     

Regiospecific Intestinal Absorption of the HIV Protease Inhibitor L-735,524 in Beagle Dogs

Purpose. To evaluate regional intestinal absorption and the feasibility of sustained release dosage form development for an HIV protease inhibitor, L-735,524. Methods. L-735,524 free base or sulfate salt was administered orally as suspension, solution or in solid dosage forms to fasted or fed Beagle dogs. Delayed-release dosage forms with slow or fast in vitro dissolution rates were evaluated in vivo to assess plasma concentration profiles. In addition, drug was administered directly into the jejunum or colon of animals, and drug concentrations determined in portal circulation to characterize absorption from these sites. Results. L-735,524 sulfate was well absorbed orally from a solution or capsule formulation if fasted animals' stomachs were preacidified with citric acid solution. A free base suspension, delivered in divided doses to fed animals, was also well absorbed. Prototype extended release dosage forms of L-735,524 produced a reduction in peak plasma levels but failed to prolong absorption and extend plasma concentrations compared to an immediate release capsule. Administration of L-735,524 sulfate solution (pH<3) as bolus solution or by infusion into the jejunum resulted in rapid but incomplete absorption compared to oral gavage. The free base suspension (pH 6.5) delivered into jejunal or colonic regions did not produce measurable systemic plasma concentrations. Conclusions. Extended release formulations did not prolong absorption of L-735,524 in dogs. Optimal L-735,524 absorption was dependent on solubility in an acidic environment in the duodenum.     

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 vitroBSA 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 m to 282.7 m. The average diameter of the composite microspheres was 180 m. 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.