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

Journey to the Market: The Evolution of Biodegradable Drug Delivery Systems

Biodegradable polymers have been used as carriers in drug delivery systems for more than four decades. Early work used crude natural materials for particle fabrication, whereas more recent work has utilized synthetic polymers. Applications include the macroscale, the microscale, and the nanoscale. Since pioneering work in the 1960’s, an array of products that use biodegradable polymers to encapsulate the desired drug payload have been approved for human use by international regulatory agencies. The commercial success of these products has led to further research in the field aimed at bringing forward new formulation types for improved delivery of various small molecule and biologic drugs. Here, we review recent advances in the development of these materials and we provide insight on their drug delivery application. We also address payload encapsulation and drug release mechanisms from biodegradable formulations and their application in approved therapeutic products.

Release mechanisms and applications of drug delivery systems for extended-release

INTRODUCTION

Drug delivery systems with extended-release profiles are ideal in improving patient compliance with enhanced efficacy. To develop devices capable of a prolonged delivery kinetics, it is crucial to understand the various underlying mechanisms contributing to extended drug release and the impact thereof on modulating the long-term performance of such systems in a practical application environment.

AREAS COVERED

This review article intends to provide a comprehensive summary of release mechanisms in extended-release drug delivery systems, particularly polymer-based systems; however, other material types will also be mentioned. Selected current research in the delivery of small molecule drugs and macromolecules is highlighted. Emphasis is placed on the combined impact of different release mechanisms and drug properties on the long-term release kinetics in vitro and in vivo.

EXPERT OPINION

The development of drug delivery systems over an extended duration is promising but also challenging when considering the numerous interrelated delivery-related parameters. Achieving a well-controlled extended drug release requires advanced techniques to minimize burst release and lag phase, a better understanding of the dynamic interrelationship between drug properties and release profiles over time, and a thorough elucidation of the impact of multiple in vivo conditions to methodically evaluate the eventual clinical efficacy.

Poly(lactic-co-glycolic acid) devices: Production and applications for sustained protein delivery

Injectable or implantable poly(lactic-co-glycolic acid) (PLGA) devices for the sustained delivery of proteins have been widely studied and utilized to overcome the necessity of repeated administrations for therapeutic proteins due to poor pharmacokinetic profiles of macromolecular therapies. These devices can come in the form of microparticles, implants, or patches depending on the disease state and route of administration. Furthermore, the release rate can be tuned from weeks to months by controlling the polymer composition, geometry of the device, or introducing additives during device fabrication. Slow-release devices have become a very powerful tool for modern medicine. Production of these devices has initially focused on emulsion-based methods, relying on phase separation to encapsulate proteins within polymeric microparticles. Process parameters and the effect of additives have been thoroughly researched to ensure protein stability during device manufacturing and to control the release profile. Continuous fluidic production methods have also been utilized to create protein-laden PLGA devices through spray drying and electrospray production. Thermal processing of PLGA with solid proteins is an emerging production method that allows for continuous, high-throughput manufacturing of PLGA/protein devices. Overall, polymeric materials for protein delivery remain an emerging field of research for the creation of single administration treatments for a wide variety of disease. This review describes, in detail, methods to make PLGA devices, comparing traditional emulsion-based methods to emerging methods to fabricate protein-laden devices. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Implantable Materials and Surgical Technologies > Nanomaterials and Implants Biology-Inspired Nanomaterials > Peptide-Based Structures.

Microscale polymer bottles corked with a phase-change material for temperature-controlled release

Keep your wine chilled! Microscale polystyrene (PS) bottles are loaded with dye molecules and then corked with a phase-change material (PCM). When the temperature is raised beyond its melting point, the PCM quickly melts and triggers an instant release of the encapsulated dye. The release profiles can be manipulated by using a binary mixture of PCMs with different melting points.

Depot versus daily administration of gonadotrophin-releasing hormone agonist protocols for pituitary down regulation in assisted reproduction cycles

BACKGROUND

Gonadotrophin-releasing hormone agonist (GnRHa) is commonly used to switch off (down regulate) the pituitary gland and thus suppress ovarian activity in women undergoing in vitro fertilisation (IVF). Other fertility drugs (gonadotrophins) are then used to stimulate ovulation in a controlled manner. Among the various types of pituitary down regulation protocols in use, the long protocol achieves the best clinical pregnancy rate. The long protocol requires GnRHa administration until suppression of ovarian activity occurs, within approximately 14 days. GnRHa can be used either as daily low-dose injections or through a single injection containing higher doses of the drug (depot). It is unclear which of these two forms of administration is best, and whether single depot administration may require higher doses of gonadotrophins.

OBJECTIVES

To compare the effectiveness and safety of a single depot dose of GHRHa versus daily GnRHa doses in women undergoing IVF.

SEARCH METHODS

We searched the following databases: Cochrane Menstrual Disorders and Subfertility Group Trials Register (searched July 2012), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2012, Issue 7), MEDLINE (1966 to July 2012), EMBASE (1980 to July 2012) and LILACS (1982 to July 2012). We also screened the reference lists of articles.

SELECTION CRITERIA

We included RCTs comparing depot and daily administration of GnRHa for long protocols in IVF treatment cycles in couples with any cause of infertility, using various methods of ovarian stimulation. The primary review outcomes were live birth or ongoing pregnancy, clinical pregnancy and ovarian hyperstimulation syndrome (OHSS). Other outcomes included number of oocytes retrieved, miscarriage, multiple pregnancy, number of gonadotrophin (FSH) units used for ovarian stimulation, duration of gonadotrophin treatment, cost and patient convenience.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, extracted data and assessed study quality. For dichotomous outcomes, we calculated odds ratios (ORs) and 95% confidence intervals (CIs) per woman randomised. Where appropriate, we pooled studies.

MAIN RESULTS

Sixteen studies were eligible for inclusion (n = 1811 participants), 12 (n = 1366 participants) of which were suitable for meta-analysis. No significant heterogeneity was detected.There were no significant differences between depot GnRHa and daily GnRHa in live birth/ongoing pregnancy rates (OR 0.95, 95% CI 0.70 to 1.31, seven studies, 873 women), but substantial differences could not be ruled out. Thus for a woman with a 24% chance of achieving a live birth or ongoing pregnancy using daily GnRHa injections, the corresponding chance using GnRHa depot would be between 18% and 29%.There was no significant difference between the groups in clinical pregnancy rate (OR 0.96, 95% CI 0.75 to 1.23, 11 studies, 1259 women). For a woman with a 30% chance of achieving clinical pregnancy using daily GnRHa injections, the corresponding chance using GnRHa depot would be between 25% and 35%.There was no significant difference between the groups in the rate of severe OHSS (OR 0.84, 95% CI 0.29 to 2.42, five studies, 570 women), but substantial differences could not be ruled out. For a woman with a 3% chance of severe OHSS using daily GnRHa injections, the corresponding risk using GnRHa depot would be between 1% and 6%.Compared to women using daily GnRHa, those on depot administration required significantly more gonadotrophin units for ovarian stimulation (standardised mean difference (SMD) 0.26, 95% CI 0.08 to 0.43, 11 studies, 1143 women) and a significantly longer duration of gonadotrophin use (mean difference (MD) 0.65, 95% CI 0.46 to 0.84, 10 studies, 1033 women).Study quality was unclear due to poor reporting. Only four studies reported live births as an outcome and only five described adequate methods for concealment of allocation.

AUTHORS' CONCLUSIONS

We found no evidence of a significant difference between depot and daily GnRHa use for pituitary down regulation in IVF cycles using the long protocol, but substantial differences could not be ruled out. Since depot GnRHa requires more gonadotrophins and a longer duration of use, it may increase the overall costs of IVF treatment.

Sustained-release delivery of octreotide from biodegradable polymeric microspheres

The study reports on the drug release behavior of a potent synthetic somatostatin analogue, octreotide acetate, from biocompatible and biodegradable microspheres composed of poly-lactic-co-glycolic acid (PLGA) following a single intramuscular depot injection. The serum octreotide levels of three Oakwood Laboratories formulations and one Sandostatin LAR(®) formulation were compared. Three formulations of octreotide acetate-loaded PLGA microspheres were prepared by a solvent extraction and evaporation procedure using PLGA polymers with different molecular weights. The in vivo drug release study was conducted in male Sprague-Dawley rats. Blood samples were taken at predetermined time points for up to 70 days. Drug serum concentrations were quantified using a radioimmunoassay procedure consisting of radiolabeled octreotide. The three octreotide PLGA microsphere formulations and Sandostatin LAR(®) all showed a two-phase drug release profile (i.e., bimodal). The peak serum drug concentration of octreotide was reached in 30 min for all formulations followed by a decline after 6 h. Following this initial burst and decline, a second-release phase occurred after 3 days. This second-release phase exhibited sustained-release behavior, as the drug serum levels were discernible between days 7 and 42. Using pharmacokinetic computer simulations, it was estimated that the steady-state octreotide serum drug levels would be predicted to fall in the range of 40-130 pg/10 μL and 20-100 pg/10 μL following repeat dosing of the Oakwood formulations and Sandostatin LAR(®) every 28 days and every 42 days at a dose of 3 mg/rat, respectively.

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.

Quantifying drug release from PLGA nanoparticulates

The objective of this work was to investigate the mechanism of release of active pharmaceutical ingredients (APIs) both small molecules (ketoprofen, indomethacin, coumarin-6) and macromolecules (human serum albumin, ovalbumin), from PLGA (50:50) nanoparticulates (400-700nm), having drug loadings less than 10%. The nanoparticulates were prepared by emulsification/solvent evaporation methods and release determined in phosphate buffer pH 7.4 at 37 degrees C. The release profiles exhibited an initial burst release phase, a slower lag phase and a second increased release rate phase. The profiles were consistent with a model in which the first phase of the release reflects diffusion controlled dissolution of drug accessible to the solid/dissolution medium interface and the second phase reflects release of drug entrapped in the polymer, the release of which was dependent on the bulk degradation of the polymer. The burst phase tended to increase with increase in API loading and solubility. The polymer erosion related parameters also indicated that increased drug loading accelerated this phase of API release. Small acidic hydrophobic actives such as ketoprofen and indomethacin had a much greater effect on these parameters than the larger hydrophilic more neutral proteins, HSA and ovalbumin.

Biodegradable polymeric nanocarriers for pulmonary drug delivery

BACKGROUND

Pulmonary drug delivery is attractive for both local and systemic drug delivery as a non-invasive route that provides a large surface area, thin epithelial barrier, high blood flow and the avoidance of first-pass metabolism.

OBJECTIVE

Nanoparticles can be designed to have several advantages for controlled and targeted drug delivery, including controlled deposition, sustained release, reduced dosing frequency, as well as an appropriate size for avoiding alveolar macrophage clearance or promoting transepithelial transport.

METHODS

This review focuses on the development and application of biodegradable polymers to nanocarrier-based strategies for the delivery of drugs, peptides, proteins, genes, siRNA and vaccines by the pulmonary route.

RESULTS/CONCLUSION

The selection of natural or synthetic materials is important in designing particles or nanoparticle clusters with the desired characteristics, such as biocompatibility, size, charge, drug release and polymer degradation rate.

Preparation of bovine serum albumin loaded poly (D, L-lactic-co-glycolic acid) microspheres by a modified phase separation technique

BSA-loaded mcirospheres were prepared by a modified phase separation method, in which petroleum ether (PE) containing a certain amount of Span 80 rather than poly (dimethylsiloxane) (PDMS) was adopted as coacervating agent. Process parameters such as Span 80 concentration, the volume and addition rate of coacervating agent, polymer concentration, agitation rate during the phase separation process and PE type were evaluated to optimize the protein encapsulation. It was found microspheres with high yield (>80.0%) and entrapment efficiency (>90%) could be obtained using PE containing 5.0% Span 80 as the coacervating agent. Microspheres with small particle size (<10 microm) could be produced successfully with appropriate process parameters. In vitro release study suggested that burst release was significantly influenced by Span 80 concentration, polymer concentration and PE type and the burst release could be reduced to <20% with optimized formulation. A biphasic release behavior in vitro test was observed for the microspheres prepared by this method. GC analysis demonstrated that residual solvent of DCM and petroleum ether was decreased dramatically in comparison with PDMS used as a conventional coacervating agent.

Principles of encapsulating hydrophobic drugs in PLA/PLGA microparticles

Injectable biodegradable and biocompatible copolymers of lactic and glycolic acid (PLGA) are an important advanced delivery system for week-to-month controlled release of hydrophobic drugs (e.g., from biopharmaceutical classification system class IV), which often display poor oral bioavailability. The basic principles and considerations to develop such microparticle formulations is reviewed here based on a comprehensive study of papers and patents from the beginnings of hydrophobic drug encapsulation in polylactic acid and PLGA up through the very recent literature. Challenges with the diversity of drug properties, microencapsulation methods, and organic solvents are evaluated in light of the precedence of commercialized formulations and with a focus on decreasing the time to lab-scale encapsulation of water-insoluble drug candidates in the early stage of drug development. The influence of key formulation variables on final microparticle characteristics, and how best to avoid undesired microparticle properties, is analyzed mechanistically. Finally, concepts are developed to manage the common issues of maintaining sink conditions for in vitro drug release assays of hydrophobic compounds. Overall, against the backdrop of an increasing number of new, poorly orally available drug entities entering development, microparticle delivery systems may be a viable strategy to rescue an otherwise undeliverable substance.

Efficacy of ciprofloxacin implants in treating experimental osteomyelitis

Ciprofloxacin (CFX) implants containing poly(D,L-lactide) and calcium phosphates (tricalcium phosphate and hydroxyapatite) was evaluated in 50 rabbits in an experimental osteomyelitis model. Their femoral cavity was inoculated with Staphylococcus aureus. After 2 weeks, the infected focus was cleaned out and the delivery system implanted. The infection and subsequent response to treatment were evaluated by microbiological analysis, biochemical and hematological markers, body weight, temperature, clinical signs, X-rays, and histology. Infected bone cultures, treated with CFX implants, showed reduced bacterial growth against controls. All CFX was released within 6 weeks. All animals recovered within 4 weeks. Even 12 weeks after implantation, no recurrence of infection was observed. Serum C-reactive protein, platelet, and leukocyte levels increased in all animals before treatment, and 4 weeks after it were maintained or rose in control animals, while decreased to normal levels in treated ones. Body weight was characterized by pretreatment losses, then gains during recuperation, or further loss in untreated animals; with no significant intraindividual differences in body temperature. Body weight, leucocytes, platelets, and C-reactive protein turned out to be highly useful markers for monitoring this kind of infection and its treatment. CFX implants demonstrated to be an effective therapy for S. aureus bone infection. Their efficacy was also reflected in decreasing severity of clinical signs, nonprogress of radiological signs indicative of infection, and good integration into bone structure. Histological examination revealed repair, with new bone formation extending into implants.