Role of in vitro release models in formulation development and quality control of parenteral depots

Assessment of subcutaneously administered insulins using in vitro release cartridge: Medium composition and albumin binding

Biotherapeutics is the fastest growing class of drugs administered by subcutaneous injection. In vitro release testing mimicking physiological conditions at the injection site may guide formulation development and improve biopredictive capabilities. Here, anin vitrorelease cartridge (IVR cartridge) comprising a porous agarose matrix emulating subcutaneous tissue was explored. The objective was to assess effects of medium composition and incorporation of human serum albumin into the matrix. Drug disappearance was assessed for solution, suspension and in situ precipitating insulin products (Actrapid, Levemir, Tresiba, Mixtard 30, Insulatard, Lantus) using the flow-based cartridge. UV-Vis imaging and light microscopy visualized dissolution, precipitation and albumin binding phenomena at the injection site. Divalent cations present in the release medium resulted in slower insulin disappearance for suspension-based and in situ precipitating insulins. Albumin-binding acylated insulin analogs exhibited rapid disappearance from the cartridge; however, sustained retention was achieved by coupling albumin to the matrix. An in vitro-in vivorelation was established for the non-albumin-binding insulins.The IVR cartridge is flexible with potential in formulation development as shown by the ability to accommodate solutions, suspensions, and in situ forming formulations while tailoring of the system to probe in vivo relevant medium effects and tissue constituent interactions.

Tricaprylin-based drug crystalline suspension for intramuscular long-acting delivery of entecavir with alleviated local inflammation

In order to ensure prolonged pharmacokinetic profile along with local tolerability at the injection site, tricaprylin-based drug crystalline suspension (TS) was designed and its local distribution, pharmacokinetics, and inflammatory response, were evaluated with conventional aqueous suspension (AS). As model drug particles, entecavir 3-palmitate (EV-P), an ester lipidic prodrug for entecavir (EV), was employed. The EV-P-loaded TS was prepared by ultra-sonication method. Prepared TS and conventional AS exhibited comparable morphology (rod or rectangular), median diameter (2.7 and 2.6 μm), crystallinity (melting point of 160-165°C), and in vitro dissolution profile. However, in vivo performances of drug microparticles were markedly different, depending on delivery vehicle. At AS-injected site, drug aggregates of up to 500 μm were formed upon intramuscular injection, and were surrounded with inflammatory cells and fibroblastic bands. In contrast, no distinct particle aggregation and adjacent granulation was observed at TS-injected site, with >4 weeks remaining of the oily vehicle in micro-computed tomographic observation. Surprisingly, TS exhibited markedly alleviated local inflammation compared to AS, endowing markedly lessened necrosis, fibrosis thickness, inflammatory area, and macrophage infiltration. The higher initial systemic exposure was observed with TS compared to AS, but TS provided prolonged delivery of EV for 3 weeks. Therefore, we suggest that the novel TS system can be a promising tool in designing parenteral long-acting delivery, with improved local tolerability.

Development of a physiologically-based pharmacokinetic model to simulate the pharmacokinetics of intramuscular antiretroviral drugs

There is growing interest in the use of long-acting (LA) injectable drugs to improve treatment adherence. However, their long elimination half-life complicates the conduct of clinical trials. Physiologically-based pharmacokinetic (PBPK) modeling is a mathematical tool that allows to simulate unknown clinical scenarios for LA formulations. Thus, this work aimed to develop and verify a mechanistic intramuscular PBPK model. The framework describing the release of a LA drug from the depot was developed by including both the physiology of the injection site and the physicochemical properties of the drug. The framework was coded in Matlab® 2020a and implemented in our existing PBPK model for the verification step using clinical data for LA cabotegravir, rilpivirine, and paliperidone. The model was considered verified when the simulations were within twofold of observed data. Furthermore, a local sensitivity analysis was conducted to assess the impact of various factors relevant for the drug release from the depot on pharmacokinetics. The PBPK model was successfully verified since all predictions were within twofold of observed clinical data. Peak concentration, area under the concentration-time curve, and trough concentration were sensitive to media viscosity, drug solubility, drug density, and diffusion layer thickness. Additionally, inflammation was shown to impact the drug release from the depot. The developed framework correctly described the release and the drug disposition of LA formulations upon intramuscular administration. It can be implemented in PBPK models to address pharmacological questions related to the use of LA formulations.

Recent advances in lipid-based long-acting injectable depot formulations

Long-acting injectable (LAIs) delivery systems sustain the drug therapeutic action in the body, resulting in reduced dosage regimen, toxicity, and improved patient compliance. Lipid-based depots are biocompatible, provide extended drug release, and improve drug stability, making them suitable for systemic and localized treatment of various chronic ailments, including psychosis, diabetes, hormonal disorders, arthritis, ocular diseases, and cancer. These depots include oil solutions, suspensions, oleogels, liquid crystalline systems, liposomes, solid lipid nanoparticles, nanostructured lipid carriers, phospholipid phase separation gel, vesicular phospholipid gel etc. This review summarizes recent advancements in lipid-based LAIs for delivering small and macromolecules, and their potential in managing chronic diseases. It also provides an overview of the lipid depots available in market or clinical phase, as well as patents for lipid-based LAIs. Furthermore, this review critically discusses the current scenario of using in vitro release methods to establish IVIVC and highlights the challenges involved in developing lipid-based LAIs.

Folic Acid-Grafted Chitosan-Alginate Nanocapsules as Effective Targeted Nanocarriers for Delivery of Turmeric Oil for Breast Cancer Therapy

Folate receptors (FRs) highly expressed in breast cancers can be used as a recognized marker for preventing off-target delivery of chemotherapeutics. In this study, folic acid (FA)-grafted chitosan-alginate nanocapsules (CS-Alg-NCs) loaded with turmeric oil (TO) were developed for breast cancer targeting. CS was successfully conjugated with FA via an amide bond with a degree of substitution at 12.86%. The TO-loaded FA-grafted CS-Alg-NCs (TO-FA-CS-Alg-NCs) optimized by Box-Behnken design using response surface methodology had satisfactory characteristics with homogenous particle size (189 nm) and sufficient encapsulation efficiency and loading capacity (35.9% and 1.82%, respectively). In vitro release study of the optimized TO-FA-CS-Alg-NCs showed a sustained TO release following the Korsmeyer-Peppas model with a Fickian diffusion mechanism at pH 5.5 and 7.4. The TO-FA-CS-Alg-NCs showed lower IC₅₀ than ungrafted TO-CS-Alg-NCs and unencapsulated TO against MDA-MB-231 and MCF-7 breast cancer cells, suggesting that FA-CS-Alg-NCs can improve anticancer activity of TO through its active targeting to the high FRs expressing breast cancers.

Microfluidic Systems For Manufacturing of Microparticle-Based Drug-Delivery Systems: Design, Construction, and Operation

Particles synthesized from biodegradable polymers hold great potential as controlled drug delivery systems. Continuous flow platforms based on microfluidics offer attractive advantages over conventional batch-emulsification techniques for the scalable fabrication of drug-loaded particles with controlled physicochemical properties. However, widespread utilization of microfluidic technologies for the manufacturing of drug-loaded particles has been hindered largely by the lack of practical guidelines toward cost-effective development and reliable operation of microfluidic systems. Here, we present a framework for rational design and construction of microfluidic systems using commercially available components for high-throughput production of uniform biodegradable particles encapsulating drugs. We also demonstrate successful implementation of this framework to devise a robust microfluidic system that is capable of producing drug-carrying particles with desired characteristics. The guidelines provided in this study will likely help broaden the applicability of microfluidic technologies for the synthesis of high-quality, drug-loaded biodegradable particles.

Biopredictive tools for the development of injectable drug products

INTRODUCTION

Biopredictive release tests are commonly used in the evaluation of oral medicines. They support decision-making in formulation development and allow predictions of the expected in-vivo performances. So far, there is limited experience in the application of these methodologies to injectable drug products.

AREAS COVERED

Parenteral drug products cover a variety of dosage forms and administration sites including subcutaneous, intramuscular, and intravenous injections. In this area, developing biopredictive and biorelevant methodologies often confronts us with unique challenges and knowledge gaps. Here, we provide a formulation-centric approach and explain the key considerations and workflow when designing biopredictive assays. Also, we outline the key role of computational methods in achieving clinical relevance and put all considerations into context using liposomal nanomedicines as an example.

EXPERT OPINION

Biopredictive tools are the need of the hour to exploit the tremendous opportunities of injectable drug products. A growing number of biopharmaceuticals such as peptides, proteins, and nucleic acids require different strategies and a better understanding of the influences on drug absorption. Here, our design strategy must maintain the balance of robustness and complexity required for effective formulation development.

In vitro release testing method development for long-acting injectable suspensions

Long-acting injectable (LAI) suspensions are complex parenterals intended to control drug release over a duration of weeks to months. Any unpredictive drug release behavior may cause serious side effects. Therefore, it is important to understand the in vitro and in vivo performance, as well as the in vitro-in vivo correlation (IVIVC) of these products. There are some US FDA recommended in vitro release testing methods for LAI suspensions. However, the release duration of all the recommended methods is less than two days which may not be appropriate for the establishment of IVIVCs for LAIs considering that their in vivo efficacies range from weeks to months. To develop in vitro release testing methods that may better correlate with in vivo release with longer durations, three compositionally equivalent medroxyprogesterone acetate suspensions were prepared with different particle size, using Depo-SubQ Provera 104® as the reference listed drug (RLD). Four different methods based on USP apparatus 2 (with dialysis sacs, enhancer cells or in-house designed devices) and USP apparatus 4 (with semisolid adapters) were utilized. USP apparatus 2 with enhancer cells and USP apparatus 4 with semisolid adapters showed the best discriminatory ability and reproducibility for the LAI suspensions investigated.

Novel adapter method for in vitro release testing of in situ forming implants

In situ forming implants are injectable liquid formulations which form solid or semisolid depots following injection. This allows for minimally invasive administration, localized drug delivery, and extended drug release. Unfortunately, this drug delivery strategy lacks standardized in vitro dissolution methods due to the difficulties in recreating implant formation in vitro that is biomimicry and with reproducible and controllable shape and dimensions. In the present study, an innovative, adapter-based in vitro release testing method was developed to solve this problem. Two distinctively different in situ forming implants (a risperidone formulation (suspension) consisting of PLGA dissolved in N-methyl pyrrolidone (NMP), where risperidone powder was suspended to form a drug suspension, and a naproxen formulation (solution) consisting of PLGA dissolved in NMP, where naproxen was completely dissolved to form a solution), were used as model in situ-forming implants. The results revealed that the implants formed in the custom-designed adapter with a water-dissolvable polyvinyl alcohol (PVA) film were bio-mimicking and reproducible in both shape and burst release of drug according to rabbit data. For both the suspension and solution formulations, this adapter-based in vitro release testing method resulted in consistent release data. Compared with a direct injection in vitro release testing method, the release profiles generated using the adapter-based method were capable of distinguishing the different release phases (initial release within 24 h, diffusion-facilitated release, and degradation-controlled release). In addition, the adapter-based method could discriminate formulation and dissolution apparatus changes and could be utilized to develop accelerated release testing methods. This adapter-based method has the promise of wide use in release testing of in situ forming implant formulations and has the potential to be used in the development of in vivo-predictive in vitro release methods.

Drug release from in situ forming implants and advances in release testing

In situ forming implants, defined as liquid formulations that generate solid or semisolid depots following administration, have shown a range of advantages in drug delivery. This drug delivery strategy allows localized delivery, sustained drug release over periods of days to months, and is a less invasive option compared to traditional solid implants which typically require surgical implantation. Unfortunately, there are a number of quality control challenges in terms of drug release testing of these delivery systems which is likely to have contributed to the relatively few commercially available in situ forming implant products. This article reviews current marketed in situ forming implant products, FDA guidance on in vitro release testing, and formulation and environmental parameters influencing drug release from in situ forming implants. Formulation considerations for development of biological agents loaded in situ forming implants are also discussed. The advantages and limitations of typically used in vitro release testing methods are summarized. Difficulties in the development of in vitro-in vivo correlations (IVIVCs) for in situ forming implant are discussed. The knowledge presented will be helpful for the development of in situ forming implants, as well as for the development of appropriate in vitro testing methods and IVIVCs.

Application of UV dissolution imaging to pharmaceutical systems

UV-vis spectrometry is widely used in the pharmaceutical sciences for compound quantification, alone or in conjunction with separation techniques, due to most drug entities possessing a chromophore absorbing light in the range 190-800 nm. UV dissolution imaging, the scope of this review, generates spatially and temporally resolved absorbance maps by exploiting the UV absorbance of the analyte. This review aims to give an introduction to UV dissolution imaging and its use in the determination of intrinsic dissolution rates and drug release from whole dosage forms. Applications of UV imaging to non-oral formulations have started to emerge and are reviewed together with the possibility of utilizing UV imaging for physical chemical characterisation of drug substances. The benefits of imaging drug diffusion and transport processes are also discussed.

Recent Progress in Drug Release Testing Methods of Biopolymeric Particulate System

Biopolymeric microparticles have been widely used for long-term release formulations of short half-life chemicals or synthetic peptides. Characterization of the drug release from microparticles is important to ensure product quality and desired pharmacological effect. However, there is no official method for long-term release parenteral dosage forms. Much work has been done to develop methods for in vitro drug release testing, generally grouped into three major categories: sample and separate, dialysis membrane, and continuous flow (flow-through cell) methods. In vitro drug release testing also plays an important role in providing insight into the in vivo performance of a product. In vitro release test with in vivo relevance can reduce the cost of conducting in vivo studies and accelerate drug product development. Therefore, investigation of the in vitro-in vivo correlation (IVIVC) is increasingly becoming an essential part of particulate formulation development. This review summarizes the principles of the in vitro release testing methods of biopolymeric particulate system with the recent research articles and discusses their characteristics including IVIVC, accelerated release testing methods, and stability of encapsulated drugs.

Challenges and opportunities in the development of complex generic long-acting injectable drug products

Long-acting injectable (LAI) drug products enable the controlled release of a drug over an extended duration of time to improve the therapeutic effect, safety profile, or administration of an injectable product. The development of generic [505(j)] and differentiated [505(b)(2)] LAI products helps to provide patients and healthcare providers with more treatment options and to reduce overall healthcare costs, including those associated with drug product administration and patient compliance. In this review, we analyze the landscape of LAI products and identify the most common technical challenges that potential generic product entrants face. We focus on five formulation technologies that account for ~90% of approved LAI products, including those eligible for generic product registration over the next five years, to illustrate technology-specific challenges. We then review efforts from the U.S. Food and Drug Administration (FDA) to promote more generic product competition and emphasize the importance of collaboration among government, industry, and academia to advance the knowledge and capabilities of the scientific community. Regulatory bodies, industry, and academia are encouraged to anticipate challenges with emerging innovative LAI technologies and to leverage the experiences built on established technologies to foster generic product development.

Multiparametric magnetic resonance imaging to characterize cabotegravir long-acting formulation depot kinetics in healthy adult volunteers

AIM

Cabotegravir long-acting (LA) intramuscular (IM) injection is being investigated for HIV preexposure prophylaxis due to its potent antiretroviral activity and infrequent dosing requirement. A subset of healthy adult volunteers participating in a Phase I study assessing cabotegravir tissue pharmacokinetics underwent serial magnetic resonance imaging (MRI) to assess drug depot localization and kinetics following a single cabotegravir LA IM targeted injection.

METHODS

Eight participants (four men, four women) were administered cabotegravir LA 600 mg under ultrasonographic-guided injection targeting the gluteal muscles. MRI was performed to determine injection-site location in gluteal muscle (IM), subcutaneous (SC) adipose tissue and combined IM/SC compartments, and to quantify drug depot characteristics, including volume and surface area, on Days 1 (≤2 hours postinjection), 3 and 8. Linear regression analysis examined correlations between MRI-derived parameters and plasma cabotegravir exposure metrics, including maximum observed concentration (C_max ) and partial area under the concentration-time curve (AUC) through Weeks 4 and 8.

RESULTS

Cabotegravir LA depot locations varied by participant and were identified in the IM compartment (n = 2), combined IM/SC compartments (n = 4), SC compartment (n = 1) and retroperitoneal cavity (n = 1). Although several MRI parameter and exposure metric correlations were determined, total depot surface area on Day 1 strongly correlated with plasma cabotegravir concentration at Days 3 and 8, C_max and partial AUC through Weeks 4 and 8.

CONCLUSION

MRI clearly delineated cabotegravir LA injection-site location and depot kinetics in healthy adults. Although injection-site variability was observed, drug depot surface area correlated with both plasma C_max and partial AUC independently of anatomical distribution.

An overview of PLGA in-situ forming implants based on solvent exchange technique: effect of formulation components and characterization

As a result of the low oral bioavailability of several drugs, there is a renewed interest for parenteral administration to target their absorption directly into the blood bypassing the long gastrointestinal route and hepatic metabolism. In order to address the potential side effects of frequent injections, sustained release systems are the most popular approaches for achieving controlled long-acting drug delivery. Injectable in-situ forming implants (ISFIs) have gained greater popularity in comparison to other sustained systems. Their significant positive aspects are attributed to easier production, acceptable administration route, reduced dosing frequency and patient compliance achievement. ISFI systems, comprising biodegradable polymers such as poly (lactide-co-glycolide) (PLGA) based on solvent exchange mechanisms, are emerged as liquid formulations that develop solid or semisolid depots after injection and deliver drugs over extended periods. The drug release from ISFI systems is generally characterized by an initial burst during the matrix solidification, followed by diffusion processes and finally polymeric degradation and erosion. The choice of suitable solvent with satisfactory viscosity, miscibility and biocompatibility along with considerable PLGA hydrophobicity and molecular weights is fundamental for optimizing the drug release. This overview gives a particular emphasis on evaluations and the wide ranges of requirements needed to achieve reasonable physicochemical characteristics of ISFIs.

Application of solid lipid nanoparticles as a long-term drug delivery platform for intramuscular and subcutaneous administration: In vitro and in vivo evaluation

The purpose of this work was to evaluate solid lipid nanoparticles (SLNs) as a long acting injectable drug delivery platform for intramuscular and subcutaneous administration. SLNs were developed with a low (unsaturated) and high (supersaturated) drug concentration at equivalent lipid doses. The impact of the drug loading as well as the administration route for the SLNs using two model compounds with different physicochemical properties were explored for their in vitro and in vivo performance. Results revealed that drug concentration had an influence on the particle size and entrapment efficiency of the SLNs and, therefore, indirectly an influence on the C_max/dose and AUC/dose after administration to rats. Furthermore, the in vitro drug release was compound specific, and linked to the affinity of the drug compounds towards the lipid matrix and release medium. The pharmacokinetic parameters resulted in an increased t_max, t_1/2 and mean residence time (MRT) for all formulations after intramuscular and subcutaneous dosing, when compared to intravenous administration. Whereas, the subcutaneous injections performed better for those parameters than the intramuscular injections, because of the higher blood perfusion in the muscles compared with the subcutaneous tissues. In conclusion, SLNs extend drug release, need to be optimized for each drug, and are appropriate carriers for the delivery of drugs that require a short-term sustained release in a timely manner.

Probabilistic modeling of an injectable aqueous crystalline suspension using influence networks

Probabilistic modeling using influence networks is an efficient, intuitive, and easy to communicate strategy in the development of complex pharmaceutical products. This study was aimed to use a risk-based approach to explore the complex interactions between product and process design parameters affecting size and shape of the particles in injectable aqueous crystalline suspensions (ACS). Based on a risk assessment, a design of experiments (DOE) was applied to evaluate the most important parameters, i.e., four critical material attributes and two critical process parameters. A model hydrophobic drug (carbamazepine) was milled and homogenized in a multistep process (dispersion and milling steps). The final formulations were characterized with automated at-line image analysis of thousands of individual particles. The particle size and shape distributions were summarized with descriptive parameters, and the relationship of these parameters and the DOE was modeled using influence networks (INs). This approach was compared and contrasted with a classical modeling approach based on multivariate linear regression (MVLR). INs had a superior visual interpretation capability of the complex and multivariate ACS system making the risk-based decision making more accessible. The probability and causality were included in the IN, i.e., the relationships between size and shape. Moreover, IN allowed to incorporate prior knowledge in a systematic way by implementing a 'black and white list'. An IN based model was created with the following model performance: a mean absolute percentage error of 1.7% and 1.1% for the size and 6.2% and 5.0% for the shape, respectively for dispersed and milled ACS. Parameters with the highest and lowest probability to control the critical quality attributes of ACS could be identified. Consequently, the parameter settings giving the optimum particle size and shape could be predicted using a Monte Carlo simulation to calculate the probability of success including the uncertainty of the model. The cubic MVLR model for the size of milled ACS was comparable to the IN in terms of the mean absolute percentage error, i.e., 1.1%. However, IN was more efficient in visualizing the complex and multivariate data set, including all the critical quality attributes and formulation/process parameters of the ACS at the same time. Moreover, the prior knowledge used in probabilistic modeling of IN could be systematically documented.

Nano Co-Crystal Embedded Stimuli-Responsive Hydrogels: A Potential Approach to Treat HIV/AIDS

Currently, the human immunodeficiency virus (HIV) that causes acquired immunodeficiency syndrome (AIDS) can only be treated successfully, using combination antiretroviral (ARV) therapy. Lamivudine (3TC) and zidovudine (AZT), two compounds used for the treatment of HIV and prevention of disease progression to AIDS are used in such combinations. Successful therapy with 3TC and AZT requires frequent dosing that may lead to reduced adherence, resistance and consequently treatment failure. Improved toxicity profiles of 3TC and AZT were observed when combined as a nano co-crystal (NCC). The use of stimuli-responsive delivery systems provides an opportunity to overcome the challenge of frequent dosing, by controlling and/or sustaining delivery of drugs. Preliminary studies undertaken to identify a suitable composition for a stimulus-responsive in situ forming hydrogel carrier for 3TC-AZT NCC were conducted, and the gelation and erosion time were determined. A 25% w/w Pluronic® F-127 thermoresponsive hydrogel was identified as a suitable carrier as it exhibited a gelation time of 5 min and an erosion time of 7 days. NCC-loaded hydrogels were evaluated using in vitro dissolution and cytotoxicity assays. In vitro dissolution undertaken using membrane-less diffusion over 168 h revealed that 3TC and AZT release from NCC-loaded hydrogels was complete and followed zero-order kinetic processes, whereas those loaded with the micro co-crystal and physical mixture were incomplete and best described using the Korsmeyer-Peppas kinetic model. The release of AZT and 3TC from the physical mixture and MCC-loaded gel exhibited a value for n of 0.595 for AZT release from the physical mixture and 0.540 for the MCC technology, whereas the release exponent for 3TC was 0.513 for the physical mixture and 0.557 for the MCC technology indicating that diffusion and erosion controlled 3TC and AZT release. In vitro cytotoxicity assay data revealed that the addition of NCC to the thermoresponsive hydrogel resulted in an improved cell viability of 88.0% ± 5.0% when compared to the cell viability of the NCC of 76.9% ± 5.0%. The results suggest that the use of a thermoresponsive nanosuspension may have the potential to be delivered as an intramuscular injection that can subsequently increase bioavailability and permit dose reduction and/or permit use of a longer dosing frequency.

In vitro release studies of furosemide reference tablets: influence of agitation rate, USP apparatus, and dissolution media

Furosemide is a diuretic drug widely used in chronic renal failure. The drug has low solubility and permeability, which cause clinical problems. Studying the in vitro release performance elucidates the rate and extent of drug dissolved from dosage forms under different conditions. Furosemide reference tablets were tested using USP Apparatuses 1 and 2 as well as the flow-through cell method (USP Apparatus 4), a dissolution apparatus that simulates the human gastrointestinal tract better than the other methods. Dissolution profiles were created with USP Apparatuses 1 and 2 at 25, 50, and 75 rpm and 900 mL of 0.1 M hydrochloric acid, acetate buffer (pH 4.5), and phosphate buffer (pH 6.8). USP Apparatus 4 with a laminar flow of 16 mL/min and 22.6 mm cells was used. Drug dissolution was quantified at 274 nm for 60 min. Mean dissolution time, dissolution efficiency, time to 50% dissolution, and time to 80% dissolution data were used to compare dissolution profiles. Additionally, zero-order, first-order, Higuchi, Hixson-Crowell, Makoid-Banakar, and Weibull models were used to adjust furosemide dissolution data. Between USP Apparatus 1 and 2, significant differences were observed in almost all parameters at 50 and 75 rpm (p < 0.05). A similar dissolution profile (f₂ > 50) with a pharmacopoeial dissolution method (USP Apparatus 2 at 50 rpm and 900 mL of phosphate buffer pH 5.8) and USP Apparatus 4 (laminar flow of 16 mL/min, 22.6 mm cells, and pH 6.8) was observed. The Weibull function was the best mathematical model to describe the in vitro release performance of furosemide in the three USP dissolution apparatuses. These results could be used to manufacture better furosemide dosage forms and decrease the negative clinical impact of current furosemide formulations.

Nanotechnology as a Platform for the Development of Injectable Parenteral Formulations: A Comprehensive Review of the Know-Hows and State of the Art

Within recent decades, the development of nanotechnology has made a significant contribution to the progress of various fields of study, including the domains of medical and pharmaceutical sciences. A substantially transformed arena within the context of the latter is the development and production of various injectable parenteral formulations. Indeed, recent decades have witnessed a rapid growth of the marketed and pipeline nanotechnology-based injectable products, which is a testimony to the remarkability of the aforementioned contribution. Adjunct to the ability of nanomaterials to deliver the incorporated payloads to many different targets of interest, nanotechnology has substantially assisted to the development of many further facets of the art. Such contributions include the enhancement of the drug solubility, development of long-acting locally and systemically injectable formulations, tuning the onset of the drug’s release through the endowment of sensitivity to various internal or external stimuli, as well as adjuvancy and immune activation, which is a desirable component for injectable vaccines and immunotherapeutic formulations. The current work seeks to provide a comprehensive review of all the abovementioned contributions, along with the most recent advances made within each domain. Furthermore, recent developments within the domains of passive and active targeting will be briefly debated.

Interpreting In Vitro Release Performance from Long-Acting Parenteral Nanosuspensions Using USP-4 Dissolution and Spectroscopic Techniques

Injectable sustained release dosage forms have emerged as desirable therapeutic routes for patients that require life-long treatments. The prevalence of drug molecules with low aqueous solubility and bioavailability has added momentum toward the development of suspension-based long-acting parenteral (LAP) formulations; the previously undesirable physicochemical properties of Biopharmaceutics Classification System (BCS) Class II/IV compounds are best suited for extended release applications. Effective in vitro release (IVR) testing of crystalline suspensions affirms product quality during early-stage development and provides connections with in vivo performance. However, before in vitro-in vivo correlations (IVIVCs) can be established, it is necessary to evaluate formulation attributes that directly affect IVR properties. In this work, a series of crystalline LAP nanosuspensions were formulated with different stabilizing polymers and applied to a continuous flow-through (USP-4) dissolution method. This technique confirmed the role of salt effects on the stability of polymer-coated nanoparticles through the detection of disparate active pharmaceutical ingredient (API) release profiles. The polymer stabilizers with extended hydrophilic chains exhibited elevated intrapolymer activity from the loss of hydrogen-bond cushioning in dissolution media with heightened ionic strength, confirmed through one-dimensional (1D) ¹H NMR and two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY) experiments. Thus, steric repulsion within the affected nanosuspensions was limited and release rates decreased. Additionally, the strength of interaction between hydrophobic polymer components and the API crystalline surface contributed to suspension dissolution properties, confirmed through solution- and solid-state spectroscopic analyses. This study provides a unique perspective on the dynamic interface between the crystalline drug and aqueous microenvironment during dissolution.

Towards in vitro in vivo correlation for modified release subcutaneously administered insulins

Therapeutic proteins and peptides are mainly administrated by subcutaneous injection. In vitro release testing of subcutaneous injectables performed using methods that take the structure and environment of the subcutaneous tissue into account may improve predictability of the in vivo behavior and thereby facilitate establishment of in vitro in vivo correlations. The aim of the study was to develop a biopredictive flow-through in vitro release method with a gel-type matrix for subcutaneously administered formulations and to explore the possibility of establishing a level A in vitro in vivo correlation for selected insulin products. A novel gel-based flow-through method with the incorporation of an injection step was used to assess selected commercial insulin formulations with different duration of action (Actrapid®, Mixtard® 30, Insulatard®, Lantus®). The in vitro release method provided the correct rank ordering in relation to the in vivo performance. For the modified release insulins Insulatard® and Lantus®, an in vitro in vivo correlation using non-linear time scaling was established based on the in vitro release data and in vivo subcutaneous absorption data of the ¹²⁵I-labeled insulins taken from literature. Predicted absorption profiles were constructed using the in vitro in vivo correlation and subsequently converted into simulated plasma profiles. The approach taken may be of wider utility in characterizing injectables for subcutaneous administration.

Regulatory aspects and quality controls of polymer-based parenteral long-acting drug products: the challenge of approving copies

To assure the safety and the efficacy of a medicinal product, quality and batch-to-batch reproducibility need to be guaranteed. In the case of parenteral long-acting products, the European Union (EU) and US Regulatory Authorities provide different indications, from the classification to the in vitro release assays related to such products. Despite their relevance, there are few in vitro experimental set-ups enabling researchers to discriminate among products with different in vivo behaviors. Consequently, most copies are authorized through hybrid instead of generic applications. Here, we review the actual regulatory frameworks to evaluate the in vitro release of drugs from polymer-based long-acting parenterals to highlight the directions followed by the Regulatory Agencies in the USA and EU.

Biorelevant release testing of biodegradable microspheres intended for intra-articular administration

Characterization of controlled release formulations used for intra-articular (IA) drug administration is challenging. Bio-relevant synovial fluids (BSF), containing physiologically relevant amounts of hyaluronic acid, phospholipids and proteins, were recently proposed to simulate healthy and osteoarthritic conditions. This work aims to evaluate the performance of different controlled release formulations of methylprednisolone (MP) for IA administration, under healthy and disease states simulated conditions. Microspheres differed in grade of poly(lactide-co-glycolide) and in the theoretical drug content (i.e. 23 or 30% w/w). Their performance was compared with the commercially available suspension of MP acetate (MPA). Under osteoarthritic state simulated condition, proteins increased the MPA release and reduced the MPA hydrolysis rate, over 48 h. Regarding microspheres, the release patterns over 40 days were significantly influenced by the composition of BSF. The pattern of the release mechanism and the amount released was affected by the presence of proteins. Protein concentration affected the release and the concentration used is critical, particularly given the relevance of the concentrations to target patient populations, i.e. patients with osteoarthritis.

A method of elevated temperatures coupled with magnetic stirring to predict real time release from long acting progesterone PLGA microspheres

The object of the study was to develop a quick and reproducible accelerated in vitro release method to predict and deduce the function of the real time (37 °C) release for long acting PLGA microspheres. The method could be described in several steps. First, the release of the microspheres were studied using the sample and separate method at 37 °C with normal orbital shaking and elevated temperatures with magnetic stirring to further accelerate the release. Second, the most similar profile at elevated temperatures with the real time release was chosen with the help of the n value in the fitted Korsmeyer-Peppas Function. Third, the Weibull function and conversion ratio were used to deduce the function of real time release according to the chosen profile at elevated temperatures. The key point in this study was to provide a quick and precise method to predict the real time release for long acting progesterone PLGA microspheres. So the elevated temperatures coupled with magnetic stirring were used to accelerate the release further, and when there have many similar release profiles with the real time release at elevated temperatures, releasing time at elevated temperatures and the R2 of the final deduced function will be used to help choosing the most similar release profile with the real time release. Four different types of progesterone PLGA microspheres were used to verify the method, and all the deduced function correlated well with the real time releases, for R 2  = 0.9912, 0.9781, 0.9918 and 0.9972, respectively.

Mathematical Models as Tools to Predict the Release Kinetic of Fluorescein from Lyotropic Colloidal Liquid Crystals

In this study, we investigated the release kinetic of fluorescein from colloidal liquid crystals made from monoglyceride and different non-ionic surfactants. The crystals were physicochemically characterized and the release experiments were carried out under the sink conditions, while mathematical models were described as extrapolations from solutions of the diffusion equation, in different initial and boundary conditions imposed by pharmaceutical formulations. The diffusion equation was solved using Laplace and Fourier transformed functions for release kinetics from infinite reservoirs in a semi-infinite medium. Solutions represents a general square root law and can be applied for the release kinetic of fluorescein from lyotropic colloidal liquid crystals. Akaike, Schwartz, and Imbimbo criteria were used to establish the appropriate mathematical model and the hierarchy of the performances of different models applied to the release experiments. The Fisher statistic test was applied to obtain the significance of differences among mathematical models. Differences of mathematical criteria demonstrated that small or no significant statistic differences were carried out between the various applied models and colloidal formulations. Phenomenological models were preferred over the empirical and semi-empirical ones. The general square root model shows that the diffusion-controlled release of fluorescein is the mathematical models extrapolated for lyotropic colloidal liquid crystals.

Subcutaneous delivery of biotherapeutics: challenges at the injection site

INTRODUCTION

Biotherapeutics are primarily delivered subcutaneously due to better compliance and prolonged rate of absorption compared to other parenteral administration routes. Recent research has allowed for the development of biotherapeutic formulations for subcutaneous delivery that require a lower frequency of administration by increasing drug half-life. Formulations determine shelf-life stability as well as features and transient behaviors that influence stability once implanted in the subcutaneous space.

AREAS COVERED

This review provides an overview of the factors affecting subcutaneous absorption with a focus on transient effects at the injection site following administration of biotherapeutics and the subsequent impact on absorption and stability.

EXPERT OPINION

Advances have been made in understanding subcutaneous tissue and the complex interplay of factors that regulate its homeostasis. The issue of poor stability after injection has been neglected, and many biotherapeutics are hampered by low bioavailability. With the advent of new in vitro techniques that account for properties of the injection site, stability studies evaluating subcutaneous tissues and impacts on pharmacokinetics of biotherapeutics may be useful in the development of new formulations.

Stimuli-responsive graphene-incorporated multifunctional chitosan for drug delivery applications: a review

INTRODUCTION

Recently, the use of chitosan (CS) in the drug delivery has reached an acceptable maturity. Graphene-based drug delivery is also increasing rapidly due to its unique physical, mechanical, chemical, and electrical properties. Therefore, the combination of CS and graphene can provide a promising carrier for the loading and controlled release of therapeutic agents.

AREAS COVERED

In this review, we will outline the advantages of this new drug delivery system (DDS) in association with CS and graphene alone and will list the various forms of these carriers, which have been studied in recent years as DDSs. Finally, we will discuss the application of this hybrid composite in other fields.

EXPERT OPINION

The introducing the GO amends the mechanical characteristics of CS, which is a major problem in the use of CS-based carriers in drug delivery due to burst release in a CS-based controlled release system through the poor mechanical strength of CS. Many related research on this area are still not fully unstated and occasionally they seem inconsistent in spite of the intent to be complementary. Therefore, a sensitive review may be needed to understand the role of graphene in CS/graphene carriers for future drug delivery applications.

Evaluation of a transtympanic delivery system in Mus musculus for extended release steroids

OBJECTIVE

The current investigation evaluated a novel extended release delivery system for treating inner ear diseases. The platform technology consists of a film forming agent (FFA) and microsphere component to localize and extend drug delivery within the ear.

STUDY DESIGN

Studies evaluated dissolution kinetics of microspheres with multiple encapsulates, testing of a variety of FFAs, and ability to localize to the round window membrane in mice in vivo.

SETTING

Studies were completed at Orbis Biosciences and The University of Kansas Medical Center.

SUBJECTS

In conjunction with in vitro characterization, an infrared dye-containing microsphere formulation was evaluated for round window membrane (RWM) localization and general tolerability in C57/BL6 Mus musculus for 35 days.

METHODS

In vitro characterization was performed using upright diffusion cells on cellulose acetate membranes, with drug content quantified by high performance liquid chromatography. Mus musculus dosing of infrared dye-containing microspheres was performed under anesthesia with a 27 GA needle and 2.0 μL injection volume RESULTS: In vitro dissolution demonstrates the ability of the FFA with microsphere platform to release steroids, proteins, peptides, and nucleic acids for at least one month, while necroscopy shows the ability of the FFA with dye-loaded microspheres to remain localized to Mus musculus RWM for the same period of time, with favorable tolerability.

CONCLUSIONS

Combining FFA and microsphere for localized drug delivery may enable cost-effective, extended release local delivery to the inner ear of new and existing small molecules, proteins, peptides, and nucleic acids.

USP Apparatus 4: a Valuable In Vitro Tool to Enable Formulation Development of Long-Acting Parenteral (LAP) Nanosuspension Formulations of Poorly Water-Soluble Compounds

Long-acting or extended release parenteral dosage forms have attracted extensive attention due to their ability to maintain therapeutic drug concentrations over long periods of time and reduce administration frequency, thus improving patient compliance. It is essential to have an in vitro release (IVR) testing method that can be used to assure product quality during routine production as well as predict and understand the in vivo performance of a formulation. The purpose of this work was to develop a discriminatory in vitro release method to guide formulation and process development of long-acting parenteral (LAP) nanosuspension formulations composed of poorly water-soluble drugs (BCS class II). Injectable nanosuspension formulations were developed to serve as test articles for method development. Several different IVR methods were evaluated for their application to the formulation screening and process development including (1) USP apparatus 2, (2) dialysis and reverse dialysis sac, and (3) continuous flow-through cell (USP apparatus 4). Preliminary data shows the promising results to support the utilization of USP 4 over more widely accepted USP 2 and dialysis methods. A combination of more representative in vivo hydrodynamics and ease of maintaining sink conditions yields the USP 4 flow-through cell method a more suitable in vitro release method for nanosuspension-based LAP formulations of poorly water-soluble compounds, such as compounds A and B.

A New Level A Type IVIVC for the Rational Design of Clinical Trials Toward Regulatory Approval of Generic Polymeric Long-Acting Injectables

Chronic neuropsychiatric disorders and diabetes mellitus affect millions of patients and require long-term supervision and expensive medical care. Although repeated drug administration can help manage these diseases, relapses and re-hospitalization owing to patient non-adherence and reduced therapeutic efficacy remain challenging. In response, long-acting injectables, which provide sustained drug release over longer periods at concentrations close to therapeutic ranges, have been proposed. Recent advancements include polymeric long-acting injectables (pLAIs), in which the active pharmaceutical ingredient (API) is encapsulated within U.S. Food and Drug Administration (FDA)-approved biocompatible polymers, such as poly(lactic-co-glycolic acid), or PLGA. Despite significant progress and development in the global pLAI market, FDA guidance for the approval of complex drug products, such as generic pLAIs, is not clearly defined. Although in vitro to in vivo correlation (IVIVC) can facilitate the identification of critical quality attributes (CQAs), drug formulations, and in vitro test platforms for evaluating drug performance in vivo, the application of IVIVC in order to shortlist time- and resource-intensive clinical trials for generic pLAIs has not been reported. Here, we propose a new Level A Type IVIVC that directly correlates the in vitro outcomes, such as drug dissolution, of candidate generic formulations with the clinical characteristics, such as drug absorption, of a reference listed drug (RLD), to help identify the specific generic pLAI formulations with clinical absorptions that are likely to be similar to that of the RLD, thereby reducing the number of clinical trials required for evaluation of clinical bioequivalence (BE). Therefore, the scope of the proposed method is intended only for the rational design of clinical trials, i.e., to shortlist the specific pLAI generic formulations for clinical BE evaluation, and not necessarily to analyze drug performances (i.e., drug safety and effectiveness) in the shortlisted clinical trials or post-approval. Once validated, this method will be of great value to developers of generic pLAIs and regulatory bodies to accelerate their approval of these generic pLAIs.

Development of a Convenient In Vitro Gel Diffusion Model for Predicting the In Vivo Performance of Subcutaneous Parenteral Formulations of Large and Small Molecules

Parenteral delivery remains a compelling drug delivery route for both large- and small-molecule drugs and can bypass issues encountered with oral absorption. For injectable drug products, there is a strong patient preference for subcutaneous administration due to its convenience over intravenous infusion. However, in subcutaneous injection, in contrast to intravenous administration, the formulation is in contact with an extracellular matrix environment that behaves more like a gel than a fluid. This can impact the expected performance of a formulation. Since typical bulk fluid dissolution studies do not accurately simulate the subcutaneous environment, improved in vitro models to help better predict the behavior of the formulation are critical. Herein, we detail the development of a new model system consisting of a more physiologically relevant gel phase to simulate the rate of drug release and diffusion from a subcutaneous injection site using agarose hydrogels as a tissue mimic. This is coupled with continuous real-time data collection to accurately monitor drug diffusion. We show how this in vitro model can be used as an in vivo performance differentiator for different formulations of both large and small molecules. Thus, this model system can be used to improve optimization and understanding of new parenteral drug formulations in a rapid and convenient manner.

Strengths, weaknesses, opportunities and challenges for long acting injectable therapies: Insights for applications in HIV therapy

Advances in solid drug nanoparticle technologies have resulted in a number of long-acting (LA) formulations with the potential for once monthly or longer administration. Such formulations offer great utility for chronic diseases, particularly when a lack of medication compliance may be detrimental to treatment response. Two such formulations are in clinical development for HIV but the concept of LA delivery has its origins in indications such as schizophrenia and contraception. Many terms have been utilised to describe the LA approach and standardisation would be beneficial. Ultimately, definitions will depend upon specific indications and routes of delivery, but for HIV we propose benchmarks that reflect perceived clinical benefits and available data on patient attitudes. Specifically, we propose dosing intervals of ≥1week, ≥1month or ≥6months, for oral, injectable or implantable strategies, respectively. This review focuses upon the critical importance of potency in achieving the LA outcome for injectable formulations and explores established and emerging technologies that have been employed across indications. Key technological challenges such as the need for consistency and ease of administration for drug combinations, are also discussed. Finally, the review explores the gaps in knowledge regarding the pharmacology of drug release from particulate-based LA injectable suspensions. A number of hypotheses are discussed based upon available data relating to local drug metabolism, active transport systems, the lymphatics, macrophages and patient-specific factors. Greater knowledge of the mechanisms that underpin drug release and protracted exposure will help facilitate further development of this strategy to achieve the promising clinical benefits.

Efficient Targeting of Adipose Tissue Macrophages in Obesity with Polysaccharide Nanocarriers

Obesity leads to an increased risk for type 2 diabetes, heart disease, stroke, and cancer. The causal link between obesity and these pathologies has recently been identified as chronic low-grade systemic inflammation initiated by pro-inflammatory macrophages in visceral adipose tissue. Current medications based on small-molecule drugs yield significant off-target side effects with long-term use, and therefore there is a major need for targeted therapies. Here we report that nanoscale polysaccharides based on biocompatible glucose polymers can efficiently target adipose macrophages in obese mice. We synthesized a series of dextran conjugates with tunable size linked to contrast agents for positron emission tomography, fluorophores for optical microscopy, and anti-inflammatory drugs for therapeutic modulation of macrophage phenotype. We observed that larger conjugates efficiently distribute to visceral adipose tissue and selectively associate with macrophages after regional peritoneal administration. Up to 63% of the injected dose remained in visceral adipose tissue 24 h after administration, resulting in >2-fold higher local concentration compared to liver, the dominant site of uptake for most nanomedicines. Furthermore, a single-dose treatment of anti-inflammatory conjugates significantly reduced pro-inflammatory markers in adipose tissue of obese mice. Importantly, all components of these therapeutic agents are approved for clinical use. This work provides a promising nanomaterials-based delivery strategy to inhibit critical factors leading to obesity comorbidities and demonstrates a unique transport mechanism for drug delivery to visceral tissues. This approach may be further applied for high-efficiency targeting of other inflammatory diseases of visceral organs.

A reproducible accelerated in vitro release testing method for PLGA microspheres

The objective of the present study was to develop a discriminatory and reproducible accelerated in vitro release method for long-acting PLGA microspheres with inner structure/porosity differences. Risperidone was chosen as a model drug. Qualitatively and quantitatively equivalent PLGA microspheres with different inner structure/porosity were obtained using different manufacturing processes. Physicochemical properties as well as degradation profiles of the prepared microspheres were investigated. Furthermore, in vitro release testing of the prepared risperidone microspheres was performed using the most common in vitro release methods (i.e., sample-and-separate and flow through) for this type of product. The obtained compositionally equivalent risperidone microspheres had similar drug loading but different inner structure/porosity. When microsphere particle size appeared similar, porous risperidone microspheres showed faster microsphere degradation and drug release compared with less porous microspheres. Both in vitro release methods investigated were able to differentiate risperidone microsphere formulations with differences in porosity under real-time (37 °C) and accelerated (45 °C) testing conditions. Notably, only the accelerated USP apparatus 4 method showed good reproducibility for highly porous risperidone microspheres. These results indicated that the accelerated USP apparatus 4 method is an appropriate fast quality control tool for long-acting PLGA microspheres (even with porous structures).

In vitro-in vivo correlation for complex non-oral drug products: Where do we stand?

In vitro–in vivo correlation (IVIVC) is a predictive mathematical model describing the relationship between an in vitro property and a relevant in vivo response of drug products. Since the U.S. Food and Drug Administration (FDA) published a regulatory guidance on the development, evaluation, and applications of IVIVC for extended release (ER) oral dosage forms in 1997, IVIVC has been one of the most important issues in the field of pharmaceutics. However, even with the aid of the FDA IVIVC Guidance, only very limited Abbreviated New Drug Application (ANDA) submission for ER oral drug products included adequate IVIVC data to enable the completion of bioequivalence (BE) review within first review cycle. Establishing an IVIVC for non-oral dosage forms has remained extremely challenging due to their complex nature and the lack of in vitro release methods that are capable of mimicking in vivo drug release conditions. This review presents a general overview of recent advances in the development of IVIVC for complex non-oral dosage forms (such as parenteral polymeric microspheres/implants, and transdermal formulations), and briefly summarizes the knowledge gained over the past two decades. Lastly this review discusses possible directions for future development of IVIVC for complex non-oral dosage forms.

In vitro-in vivo correlation of parenteral risperidone polymeric microspheres

The objective of the present study was to determine whether an in vitro-in vivo correlation (IVIVC) can be established for polymeric microspheres that are equivalent in formulation composition but prepared with different manufacturing processes. Risperidone was chosen as a model therapeutic and poly(lactic-co-glycolic acid) (PLGA) with similar molecular weight as that used in the commercial product Risperdal® Consta® was used to prepare risperidone microspheres. Various manufacturing processes were investigated to produce the risperidone microspheres with similar drug loading (approx. 37%) but distinctly different physicochemical properties (e.g. porosity, particle size and particle size distribution). In vitro release of the risperidone microspheres was investigated using different release testing methods (such as sample-and-separate and USP apparatus 4). In vivo pharmacokinetic profiles of the risperidone microsphere formulations following intramuscular administration were determined using a rabbit model. Furthermore, the obtained pharmacokinetic profiles were deconvoluted using the Loo-Riegelman method and the calculated in vivo release was compared with the in vitro release of these microspheres. Level A IVIVCs were established and validated for the compositionally equivalent risperidone microspheres based on the in vitro release data obtained using USP apparatus 4. The developed IVIVCs demonstrated good predictability and were robust. These results showed that the developed USP apparatus 4 method was capable of discriminating PLGA microspheres that are equivalent in formulation composition but with manufacturing differences and predicting their in vivo performance in the investigated animal model.

The PK-Eye: A Novel In Vitro Ocular Flow Model for Use in Preclinical Drug Development

A 2-compartment in vitro eye flow model has been developed to estimate ocular drug clearance by the anterior aqueous outflow pathway. The model is designed to accelerate the development of longer-acting ophthalmic therapeutics. Dye studies show aqueous flow is necessary for a molecule injected into the vitreous cavity to clear from the model. The clearance times of proteins can be estimated by collecting the aqueous outflow, which was first conducted with bevacizumab using phosphate-buffered saline in the vitreous cavity. A simulated vitreous solution was then used and ranibizumab (0.5 mg) displayed a clearance time of 8.1 ± 3.1 days, which is comparable to that observed in humans. The model can estimate drug release from implants or the dissolution of suspensions as a first step in their clearance mechanism, which will be the rate-limiting step for the overall resident time of a candidate dosage form in the vitreous. A suspension of triamcinolone acetonide (Kenalog®) (4.0 mg) displayed clearance times spanning 26-28 days. These results indicate that the model can be used to determine in vitro-in vivo correlations in preclinical studies to develop long-lasting therapeutics to treat blinding diseases at the back of the eye.