Measurement of drug release from microcarriers by microdialysis

Advances in in-vitro bioequivalence testing methods for complex ophthalmic generic products

The United States Food and Drug Administration (USFDA) demands that the generic industry prove topical ocular products' pharmaceutical and bioequivalence (BE). In contrast to generic oral drugs, topical ocular product BE testing has proved difficult. New generic versions are compared to an authorized drug product known as a Reference Listed Drug (RLD) to demonstrate their bioequivalence. If the excellent in-vitro results may support the presumption of equivalence in-vivo performance and the only clinically significant difference between the generic and RLD is in its physicochemical qualities and drug release rate, then in-vivo BE studies may be waived. Proving BE through dissolution tests is a golden standard for most conventional dosage forms. However, due to the limited number of biorelevant in-vitro drug release testing (IVRT) approaches capable of differentiating their performance based on product quality and physicochemical properties, the development of generic ophthalmic products has been slow and time-consuming. Often, BE of topical ophthalmic formulations cannot be proved using a single in-vitro test; therefore, an elaborated discussion on various IVRT methods performed to demonstrate bioequivalence of complex generis like ophthalmic emulsions, suspensions, ointments, and gels is necessary. This manuscript aims to review the status of biowaiver criteria for complex ophthalmic products concerning the product-specific FDA guidance to the generic industry.

A novel dermal delivery system using natural spicules for cosmetics and therapeutics

BACKGROUND

Dermal delivery is versatile in therapeutics as well as cosmetics in pursuit of enhancing safety/efficacy and alleviating pain/fear to alternate oral/injective administrations. Natural siliceous spicules offer a potential approach via simple topical medications to circumvent poor penetrations through the skin barrier by loading, carrying and releasing the active ingredients in a highly efficient and controlled manner.

AIMS

The delivery of ingredients loaded on spicules is assessed to improve the dermal efficacy compared to simple topical treatments.

METHODS

First, needle-like spicules were isolated from natural freshwater sponges. Then, the active ingredient was loaded via liposome formations. Finally, the dermal efficiency was evaluated.

RESULTS

Natural siliceous spicules were purified, sorted, and fully characterized to appear 250 μm of length and 12 μm of diameter on average. A model ingredient, pectolinarin, was efficiently loaded onto the internal space of spicules via lecithin-based liposome formations. The penetration was visualized using a porcine skin sample with a fluorescent dye and assessed quantitatively by a Franz diffusion cell system. Dermal absorption rate was measured 73.4%, while the percutaneous penetration rate was 2.2%. The release pattern turned out a simple diffusion analyzed by Fick's law and Higuchi model. The liposomes loaded onto spicules were further stabilized by a hydrophobic capsulation, which may benefit the overall efficacy of the ingredient.

CONCLUSION

A novel dermal delivery system is beneficial to improve the topical efficacy of biologically active ingredients. The outcomes shed a light upon developing skin-protective/improving cosmetics and therapeutics with enhanced performance.

Analytical characterization of liposomes and other lipid nanoparticles for drug delivery

Lipid nanoparticles, especially liposomes and lipid/nucleic acid complexed nanoparticles have shown great success in the pharmaceutical industry. Their success is attributed to stable drug loading, extended pharmacokinetics, reduced off-target side effects, and enhanced delivery efficiency to disease targets with formidable blood-brain or plasma membrane barriers. Therefore, they offer promising formulation options for drugs limited by low therapeutic indexes in traditional dosage forms and current "undruggable" targets. Recent development of siRNA, antisense oligonucleotide, or the CRISPR complex-loaded lipid nanoparticles and liposomal vaccines also shed light on their potential in enabling versatile formulation platforms for new pharmaceutical modalities. Analytical characterization of these nanoparticles is critical to drug design, formulation development, understanding in vivo performance, as well as quality control. The multi-lipid excipients, unique core-bilayer structure, and nanoscale size all underscore their complicated critical quality attributes, including lipid species, drug encapsulation efficiency, nanoparticle characteristics, product stability, and drug release. To address these challenges and facilitate future applications of lipid nanoparticles in drug development, we summarize available analytical approaches for physicochemical characterizations of lipid nanoparticle-based pharmaceutical modalities. Furthermore, we compare advantages and challenges of different techniques, and highlight the promise of new strategies for automated high-throughput screening and future development.

Role of In Vitro Release Methods in Liposomal Formulation Development: Challenges and Regulatory Perspective

In the past few years, measurement of drug release from pharmaceutical dosage forms has been a focus of extensive research because the release profile obtained in vitro can give an indication of the drug's performance in vivo. Currently, there are no compendial in vitro release methods designed for liposomes owing to a range of experimental challenges, which has created a major hurdle for both development and regulatory acceptance of liposome-based drug products. In this paper, we review the current techniques that are most often used to assess in vitro drug release from liposomal products; these include the membrane diffusion techniques (dialysis, reverse dialysis, fractional dialysis, and microdialysis), the sample-and-separate approach, the in situ method, the continuous flow, and the modified United States Pharmacopeia methods (USP I and USP IV). We discuss the principles behind each of the methods and the criteria that assist in choosing the most appropriate method for studying drug release from a liposomal formulation. Also, we have included information concerning the current regulatory requirements for liposomal drug products in the United States and in Europe. In light of increasing costs of preclinical and clinical trials, applying a reliable in vitro release method could serve as a proxy to expensive in vivo bioavailability studies. Graphical Abstract Appropriate in-vitro drug release test from liposomal products is important to predict the in-vivo performance.

IN VITRO RELEASE KINETICS MODEL FITTING OF LIPOSOMES: AN INSIGHT

Liposomes are emerging cargoes for bioactive delivery owing to their widely accepted biocompatible and biodegradable nature. It is always a challenge to control the release of payload for effective delivery to the site of interest. Over the couple of decennia, mathematical modeling of release process is a need of time whether the drug remains in the circulation or reaches at the target site. For establishing a better in vitro - in vivo correlation, release kinetics models viz. Peppas, Higuchi, Weibull, Zero Order and First order including mechanistic models like All-or-None, Toroidal, and Biomembrane models etc. are continuously exploited to predict drug release profile. Most of these models rely on the diffusion equations based on the composition of liposomes and conditions of release. Here, we summarized the crucial reports exploring these models and associated interventions to know the underlying physicochemical release phenomenon. Such mathematical model fitting can be a promising approach to deduce release/delivery process to help in designing the safe and efficacious ("Smart") liposomes.

Development of a Flow-Through USP-4 Apparatus Drug Release Assay to Evaluate Doxorubicin Liposomes

Doxil® is a complex parenteral doxorubicin (DOX) liposome formulation approved by the FDA. For generic doxorubicin liposomes, analyzing the release profile of DOX is important for quality control and comparability studies. However, there is no robust standard drug release assay available for doxorubicin liposomes. In this study, we describe a USP-4 apparatus assay capable of discriminating DOX liposomal formulations based on release profile. Establishment of the assay was hindered by limited DOX release from liposomes in physiological conditions at 37°C. The addition of NH₄HCO₃ to the release media facilitated DOX release proportionally to the salt concentration added but caused precipitation of released drug in USP-4 apparatus. Precipitation of DOX was avoided by adding hydroxypropyl-cyclodextrin (HP-CD) to the release medium. We optimized conditions for DOX release by varying a number of parameters such as: concentration of HP-CD, testing temperature, and concentration of tested samples. The optimized release medium contained: 100 mM NH₄HCO₃, 75 mM 2-(N-morpholino) ethanesulfonic acid (MES) and 5% w/v HP-CD, 5% w/v sucrose, 0.02% w/v NaN₃ (pH 6). The drug release assay was performed at 45°C. The optimized release assay can discriminate between DOX liposomal formulations of different compositions, physicochemical properties, and prepared by different manufacturing methods. This indicates that the assay could be used to compare DOX release from generic DOX formulations to the innovator product Doxil®.

Recent advances in testing of microsphere drug delivery systems

INTRODUCTION

This review discusses advances in the field of microsphere testing.

AREAS COVERED

In vitro release-testing methods such as sample and separate, dialysis membrane sacs and USP apparatus IV have been used for microspheres. Based on comparisons of these methods, USP apparatus IV is currently the method of choice. Accelerated in vitro release tests have been developed to shorten the testing time for quality control purposes. In vitro-in vivo correlations using real-time and accelerated release data have been developed, to minimize the need to conduct in vivo performance evaluation. Storage stability studies have been conducted to investigate the influence of various environmental factors on microsphere quality throughout the product shelf life. New tests such as the floating test and the in vitro wash-off test have been developed along with advancement in characterization techniques for other physico-chemical parameters such as particle size, drug content, and thermal properties.

EXPERT OPINION

Although significant developments have been made in microsphere release testing, there is still a lack of guidance in this area. Microsphere storage stability studies should be extended to include microspheres containing large molecules. An agreement needs to be reached on the use of particle sizing techniques to avoid inconsistent data. An approach needs to be developed to determine total moisture content of microspheres.

Assessing the In Vitro Drug Release from Lipid-Core Nanocapsules: a New Strategy Combining Dialysis Sac and a Continuous-Flow System

The in vitro assessment of drug release from polymeric nanocapsules suspensions is one of the most studied parameters in the development of drug-loaded nanoparticles. Nevertheless, official methods for the evaluation of drug release from submicrometric carriers are not available. In this work, a new approach to assess the in vitro drug release profile from drug-loaded lipid-core nanocapsules (LNC) was proposed. A continuous-flow system (open system) was designed to evaluate the in vitro drug release profiles from different LNC formulations containing prednisolone or clobetasol propionate (LNC-CP) as drug model (LNC-PD) using a homemade apparatus. The release medium was constantly renewed throughout the experiment. A dialysis bag containing 5 mL of formulation (0.5 mg mL(-1)) was maintained inside the apparatus, under magnetic stirring and controlled temperature (37°C). In parallel, studies based on the conventional dialysis sac technique (closed system) were performed. It was possible to discriminate the in vitro drug release profile of different formulations using the open system. The proposed strategy improved the sink condition, by constantly renewing the release medium, thus maintaining the drug concentration farther from the saturated concentration in the release medium. Moreover, problems due to sampling errors can be easily overcome using this semi-automated system, since the collection is done automatically without interference from the analyst. The system proposed in this paper brings important methodological and analytical advantages, becoming a promising prototype semi-automated apparatus for performing in vitro drug release studies from drug-loaded lipid-core nanocapsules and other related nanoparticle drug delivery systems.

Application of pharmacokinetic and pharmacodynamic analysis to the development of liposomal formulations for oncology

Liposomal formulations of anticancer agents have been developed to prolong drug circulating lifetime, enhance anti-tumor efficacy by increasing tumor drug deposition, and reduce drug toxicity by avoiding critical normal tissues. Despite the clinical approval of numerous liposome-based chemotherapeutics, challenges remain in the development and clinical deployment of micro- and nano-particulate formulations, as well as combining these novel agents with conventional drugs and standard-of-care therapies. Factors requiring optimization include control of drug biodistribution, release rates of the encapsulated drug, and uptake by target cells. Quantitative mathematical modeling of formulation performance can provide an important tool for understanding drug transport, uptake, and disposition processes, as well as their role in therapeutic outcomes. This review identifies several relevant pharmacokinetic/pharmacodynamic models that incorporate key physical, biochemical, and physiological processes involved in delivery of oncology drugs by liposomal formulations. They capture observed data, lend insight into factors determining overall antitumor response, and in some cases, predict conditions for optimizing chemotherapy combinations that include nanoparticulate drug carriers.

Comparison of in vitro dialysis release methods of loperamide-encapsulated liposomal gel for topical drug delivery

Background

The purpose of this study was to determine the most appropriate dialysis equilibrium method to assess liposomal gel formulations containing hydrophobic drugs, to give the most accurate indication of drug release.

Methods

Loperamide hydrochloride-encapsulated liposomes, composed of L-α-phosphatidylcholine and cholesterol (molar ratio of 2:1), were prepared according to the method of dried lipid film hydration. The liposomes were incorporated into a carbopol gel (0.5%, weight/weight). The release of the drug from the nanoparticles was assessed using a number of variations of the dialysis technique, taking into account solubility parameters and formulation. Method 1 (below saturation point) and Method 2 (above saturation point) used a dilution method to evaluate how drug concentration and solubility affects the in vitro drug-release profile of loperamide hydrochloride, while Methods 3 (below saturation point) and 4 (above saturation point) evaluated how drug concentration and the gel base affect the release profile.

Results

In Method 1, the liposomes showed a rapid release of just over 60% in the first 3 hours and then a slower, sustained release to just over 70% at 24 hours. Method 2 showed a gradual, sustained release profile with the liposomes with 55% release at 24 hours. In Method 3, the liposomes showed a rapid burst release of 98% at 2 hours. In Method 4, the liposomal gel had a rapid release of 60% within 3 hours and then a more gradual, sustained release with 86% release at 24 hours. The free drug suspension in Methods 2 and 4 showed a limited release across the dialysis membrane, in comparison to Methods 1 and 3, which showed a complete release in a timely manner.

Conclusion

This study has demonstrated that the actual method used for equilibrium dialysis plays a significant role in determining the true characteristics of a topical nanoformulation, with Method 3 providing the most accurate indication of the release of a hydrophobic drug from a topical liposomal formulation.

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

This review article provides an assessment of advantages/limitations of the use of current in vitro release models to predict in vivo performance of parenteral sustained release products (injectable depots). As highlighted, key characteristics influencing the in vivo drug fate may vary with the route of administration and the type of sustained release formulation. To this end, an account is given on three representative injection sites (intramuscular, subcutaneous and intra-articular) as well as on in vitro release mechanism(s) of drugs from five commonly investigated depot principles (suspensions, microspheres, hydrogels, lipophilic solutions, and liposomes/other nano-size formulations). Current in vitro release models are, to a different extent, able to mimic the rate, transport and equilibrium processes that the drug substance may experience in the environment of the administration site. Their utility for the purpose of quality control including in vitro-in vivo correlations and formulation design is discussed.

Preparation and evaluation of lyophilized liposome-encapsulated bufadienolides

OBJECTIVE

The objective of this study was to prepare bufadienolides-loaded liposome (BU-lipo).

METHODS

The BU-lipo was prepared by a thin-film hydration method involving sonication and lyophilization procedures. The lyophilized BU-lipo was characterized with regard to the appearance and particle size by scanning electron microscopy, transmission electron microscopy, and photon correlation spectroscopy. The entrapment efficiency (EE) of BU-lipo was evaluated by the microdialysis technique.

RESULTS

In the optimal formulation, Lipoid E-80 and the mass ratio of cholesterol to lipid were fixed at 1.25% and 0.05. The media diameters of BU-lipo before and after lyophilization were about 100 nm, and the EEs of bufalin (B), cinobufagin (C), and resibufogenin (R) were 86.5%, 90.0%, and 92.1%, respectively. In the EE study, the probe recoveries of B, C, and R were 21.53 +/- 1.14%, 19.49 +/- 1.34%, and 20.19 +/- 1.25%, respectively, at a flow rate of 4 microL/min by the gain method. The EE of BU-lipo evaluated by microdialysis and ultrafiltration were equivalent.

CONCLUSION

The lyophilized BU-lipo contained trehalose (10%) was stable up to 6 months in a desiccator under 2 degrees C-8 degrees C. The microdialysis technique has a wide application perspective in the investigation of the free-drug concentration of microcarrier systems.

Novel strategies to improve the anticancer action of 5-fluorouracil by using drug delivery systems

Because of the fundamental importance of new therapeutic routes for cancer treatment, a number of systems based on colloidal particles as vehicles for the delivery of the anticancer drug 5-fluorouracil have been devised. The target is always to provide the proper dose of the antitumor agent only at the desired locus of action, thus reducing the unwanted side effects. In this review, the main strategies and the more significant results in the development of 5-fluorouracil carriers for cancer treatment are discussed.

Disease guided optimization of the respiratory delivery of microparticulate formulations

BACKGROUND

Inhalation of microparticulate dosage forms can be effectively used in the treatment of respiratory and systemic diseases.

OBJECTIVE

Disease states investigated for treatment by inhalation of microparticles were reviewed along with the drugs' pharmacological, pharmacokinetic and physical chemical properties to identify the advantages of microparticulate inhalation formulations and to identify areas for further improvement.

METHODS

Microbial infections of the lung, asthma, diabetes, lung transplantation and lung cancer were examined, with a focus on those systems intended to provide a sustained release.

CONCLUSION

In developing microparticulate formulations for inhalation in the lung, there is a need to understand the pharmacology of the drug as the key to revealing the optimal concentration time profile, the disease state, and the pharmacokinetic properties of the pure drug as determined by IV administration and inhalation. Finally, in vitro release studies will allow better identification of the best dosing strategy to be used in efficacy and safety studies.

Pharmacokinetics of 5-fluorouracil in the hamster following inhalation delivery of lipid-coated nanoparticles

The inhalation delivery of 5-fluorouracil (5-FU) in lipid-coated nanoparticles (LNPs) to hamsters was evaluated to determine the feasibility for use in lung cancer chemotherapy. The inhaled dose, 30 mg LNPs/kg body weight (1.5 mg/kg 5-FU), was delivered over an 8-min interval. Fluorescein isothiocyanate dextran (FITC-dextran) was included within the LNPs to provide an estimate of the particle concentration. The concentration of FITC-dextran and total 5-FU (released and LNP-associated) was determined as a function of time in the lung, trachea, larynx, esophagus, and serum. Concentrations of 5-FU and FITC-dextran were initially high in the trachea, larynx, and esophagus, and lower in the lung. Within 24 h, greater than 99% of the LNPs were cleared from the respiratory tract and total 5-FU concentrations mirrored the LNP concentration. An eight-compartment pharmacokinetic model was used to describe the observed trends in concentrations of LNPs and total 5-FU and to estimate the released 5-FU concentration in the above tissues. From this analysis, effective local targeting as well as sustained efficacious concentrations of 5-FU in the expected tumor sites were demonstrated.

Development of a respirable, sustained release microcarrier for 5-fluorouracil I: In vitro assessment of liposomes, microspheres, and lipid coated nanoparticles

The release rate of 5-fluorouracil (5-FU) from liposomes, microspheres, and lipid-coated nanoparticles (LNPs) was determined by microdialysis to investigate their use as a respirable delivery system for adjuvant (postsurgery) therapy of lung cancer. 5-FU was incorporated into liposomes using thin film hydration and into microspheres and LNPs by spray drying. Primary particle size distributions were measured by dynamic light scattering. Liposomes released 5-FU in 4-10 h (k(1) = 0.44-2.31/h, first-order release model). Extruded vesicles with diameters less than one micron released 5-FU more quickly than nonextruded vesicles. With poly-(lactide) (PLA) and Poly-(lactide-co-glycolide) (PLGA) microspheres, slower release rates were observed (k(1) = 0.067-0.202/h). Increasing the lactide:glycolide ratio (50:50-100:0) resulted in a progressive decrease in the release rate of 5-FU. poly-(lactide-co-caprolactone) (PLCL) microspheres released 5-FU more rapidly compared to PLGA systems (k(1) = 0.254-0.259/h). LNPs formulated with polymeric core excipients had lower release rates compared to monomeric excipients (k(1) = 0.043-0.105/h vs. k(1) = 0.192-0.345/h). Changing the lipid chain length of the shell lipid components had a relatively minor effect (k(1) = 0.043-0.129/h). Overall, these systems yielded a wide range of delivery durations that may be suitable for use as an inhalation delivery system for adjuvant therapy of lung cancer.

Development of a Respirable, Sustained Release Microcarrier for 5-Fluorouracil II: In Vitro and In Vivo Optimization of Lipid Coated Nanoparticles

The release rate of 5-fluorouracil (5-FU) from lipid-coated nanoparticles (LNPs) was determined to develop a respirable delivery system for use as adjuvant (postsurgery) therapy for lung cancer. LNPs were prepared by spray drying, and the in vitro release was measured by microdialysis. The composition of the core and shell affected the release rate. Increasing the core diameter at constant shell thickness and increasing shell thickness at constant core diameter reduced the release rate, suggesting that the lipid shell is the rate limiting step for the release of 5-FU. A model consisting of a sequential zero-order/first-order dependence on time from polydispersed cores within polydispersed shells was developed to describe the release. Based on studies of the effect of geometry of the layered particles, the optimal formulation was identified as a 600-nm diameter 5-FU/poly-(glutamic acid) core with a 200-nm thick tripalmitin/cetyl alcohol shell. This system is readily aerosolized by ultrasonic atomization, which did not change the release properties. Preliminary instillation and inhalation delivery studies to the hamster resulted in lung levels of the particles and 5-FU that were near the desired values. Through this effort, a sustained-release, respirable delivery system for adjuvant therapy of lung cancer in humans may ultimately be realized.

Pharmacokinetic Study of Ketoprofen Isopropyl Ester-Loaded Lipid Microspheres in Rat Blood Using Microdialysis

A blood microdialysis technique coupled with high-performance liquid chromatography was used to investigate the pharmacokinetics of unbound ketoprofen in rats after intravenous administration of a lipid-soluble ketoprofen derivate, ketoprofen isopropyl ester (KPI), loaded into lipid microspheres (LM) and ketoprofen solution. A microdialysis probe was inserted into the jugular vein of male Wistar rats. KPI-loaded LM or ketoprofen solution (24 mg/kg, i.v.) was then administrated via a femoral vein. Dialysate samples were analyzed using HPLC. The in vitro and in vivo recovery rate of the microdialysis probe was 30.42+/-0.74% (n=3) and 40.27+/-2.74% (n=3), respectively. The pharmacokinetic parameters for ketoprofen after intravenous administration of KPI-loaded LM and ketoprofen solution exhibited no statistically significant differences. The results of this pharmacokinetic study indicate that the microdialysis technique can be widely applicable to investigations of in vivo free-drug of microcarrier systems.

Simultaneous intra-accumbens remifentanil and dopamine kinetics suggest that neither determines within-session operant responding

RATIONALE

The ultra-short-acting mu opioid agonist analgesic/anesthetic remifentanil (RMF) is extremely rapidly eliminated from blood (half-life in rats, 0.3-0.7 min). This extremely fast elimination is thought to be the main reason why RMF maintains such high rates of responding in animal operant-conditioning models of drug addiction.

OBJECTIVE

The present study investigated if such a fast elimination of RMF also occurs in the extracellular space of the brain, i.e., in the pharmacokinetic compartment that is thought to be ultimately mediating the reinforcing effect, and hence, the abuse liability of drugs.

METHODS

Nucleus accumbens (NAC) RMF and dopamine (DA) were simultaneously quantified by in vivo microdialysis followed by tandem mass spectrometry both in rats that traversed an alley to receive intravenous injections of 0.032 mg kg(-1) RMF in an operant runway procedure (contingent RMF) and in rats that passively received RMF in the runway (noncontingent RMF).

RESULTS

Regardless of the mode of administration (i.e., contingent or noncontingent), intra-accumbens RMF peaked in the first 10-min sample and decreased exponentially with a t(1/2) of 10.0+/-1.2 min (N=31). RMF-stimulated DA peaked in the 10-min sample immediately after the RMF peak and decreased with a time course very similar to that of RMF. Crosscorrelation of the NAC RMF and NAC DA curves showed them to be tightly synchronized. Noncontingent single-dose RMF was eliminated from the whole brain with a half-life of 1.1+/-0.2 min and from blood with a half-life of 0.3 min or less. The comparison of blood-vs-brain RMF pharmacokinetics with rat RMF self-administration behavior, either in operant runway (present study) or in lever-press-based operant-conditioning procedures, suggests that titration of blood RMF, whole-brain RMF, intra-accumbens RMF, or accumbal DA levels (assessed with the limited temporal resolution of in vivo microdialysis) does not determine a rat's decision to reemit a response during a multiple-injection drug self-administration session.