Accelerated in-vitro release testing methods for extended-release parenteral dosage forms

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.

Chitosan-based advanced materials for docetaxel and paclitaxel delivery: Recent advances and future directions in cancer theranostics

Paclitaxel (PTX) and docetaxel (DTX) are key members of taxanes with high anti-tumor activity against various cancer cells. These chemotherapeutic agents suffer from a number of drawbacks and it seems that low solubility in water is the most important one. Although much effort has been made in improving the bioavailability of PTX and DTX, the low bioavailability and minimal accumulation at tumor sites are still the challenges faced in PTX and DTX therapy. As a consequence, bio-based nanoparticles (NPs) have attracted much attention due to unique properties. Among them, chitosan (CS) is of interest due to its great biocompatibility. CS is a positively charged polysaccharide with the capability of interaction with negatively charged biomolecules. Besides, it can be processed into the sheet, micro/nano-particles, scaffold, and is dissolvable in mildly acidic pH similar to the pH of the tumor microenvironment. Keeping in mind the different applications of CS in the preparation of nanocarriers for delivery of PTX and DTX, in the present review, we demonstrate that how CS functionalized-nanocarriers and CS modification can be beneficial in enhancing the bioavailability of PTX and DTX, targeted delivery at tumor site, image-guided delivery and co-delivery with other anti-tumor drugs or genes.

Post-manufacture loading of filaments and 3D printed PLA scaffolds with prednisolone and dexamethasone for tissue regeneration applications

Strategies to load prednisolone or dexamethasone in preformed poly(L-lactic acid) (PLA) filaments and 3D printed scaffolds were explored as a way of personalizing the drug, the dose and the release profile for regenerative medicine purposes. Instead of starting from a PLA filament preloaded with a given content of drug, we explored two more versatile strategies. The first one involved the soaking of PLA filaments into a drug solution prepared in a solvent that reversibly swelled PLA; during 3D printing the melting of PLA contributed to the efficient integration (encapsulation) of the drug inside the printed strand. The second strategy consisted in first printing the 3D PLA scaffolds followed by soaking in a suitable drug solution in order to exploit the higher specific surface of the printed strands compared to the filament. Sustained release profiles were recorded when either prednisolone or dexamethasone were loaded in preformed PLA filaments, while rapid release was recorded for 3D PLA scaffolds loaded after printing. The combination of the two proposed methods reported here opened the possibility of creating concentration gradients of different drugs in the same scaffold exhibiting distinct release patterns. Namely, the strand core contained an active ingredient to be slowly released, while the surface was covered with other active ingredient that could be rapidly delivered. The feasibility of this approach was confirmed through dual loading of dexamethasone in the filament and of prednisolone on the preformed scaffold. Drug-loaded scaffolds were characterized in terms of printability, structural characteristics (DSC, XRD), mechanical properties, biodegradation, and ability to promote cell attachment and proliferation. Finally, anti-inflammatory response and osteoinductive properties were verified in cell cultures.

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.

Comparison of antinociceptive effects of plain lidocaine versus lidocaine complexed with hydroxypropyl-β-cyclodextrin in animal models of acute and persistent orofacial pain

Herein, it was investigated whether a complex of lidocaine with 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) would present a better antinociceptive profile in vivo when compared with plain lidocaine in models of orofacial pain. Plain lidocaine (LDC) and complexed lidocaine (LDC:HP-β-CD) were initially evaluated in vitro to determine the release rate of the two formulations. Subsequently, the effect of both formulations was evaluated in independent groups of rats submitted to the orofacial formalin test, induction of facial heat hyperalgesia by capsaicin and carrageenan, and induction of facial heat and mechanical hyperalgesia by constriction of the infraorbital nerve. LDC:HP-β-CD led to a reduction in the lidocaine release assessed in the in vitro release assay compared to plain LDC. Both formulations presented an antinociceptive effect in all models, but LDC:HP-β-CD showed a better effect in the second phase of the formalin response, in carrageenan-induced heat hyperalgesia, and in the heat hyperalgesia associated to infraorbital nerve constriction. Our results show that complexation improved in vivo antinociceptive effects of LDC, but further studies are necessary to elucidate what properties contribute to the better effect of the complexed formulation on this models and/or what characteristics of the pain model facilitate the action of the complexed formulation.

Tuning HIV drug release from a nanogel-basedin situforming implant by changing nanogel size

This paper reports anin situforming implant based on responsive nanogels that gives tuneable long-acting drug release.

Polymer nanoparticles for the intravenous delivery of anticancer drugs: the checkpoints on the road from the synthesis to clinical translation

In this review article we discuss some of the key aspects concerning the development of a polymer-based nanoparticle formulation for intravenous drug delivery. Since numerous preparations fail before and during clinical trials, our aim is to emphasize the main issues that a nanocarrier has to face once injected into the body. These include biocompatibility and toxicity, drug loading and release, nanoparticle storage and stability, biodistribution, selectivity towards the target organs or tissues, internalization in cells and biodegradability. They represent the main checkpoints to define a polymer-based formulation as safe and effective. Indeed, this review is intended to provide guidelines to be followed in the early development of a new nanotherapeutic to hopefully increase the success rate of polymer-based formulations entering clinical trials. The corresponding requirements and characteristics are discussed in the context of some relevant case studies taken from the literature and mainly related to the delivery of lipophilic anticancer therapeutics.

Surface fluorination of polylactide as a path to improve platelet associated hemocompatibility

Surface-induced thrombosis is still a significant clinical concern for many types of blood-contacting medical devices. In particular, protein adsorption and platelet adhesion are important events due to their ability to trigger the coagulation cascade and initiate thrombosis. Poly(lactic acid) (PLA) has been the predominant polymer used for making bioresorbable stents. Despite long-term advantages, these stents are associated with higher rates of early thrombosis compared with permanent metallic stents. To address this issue, we modified the surface of PLA with a perfluoro compound facilitated by surface activation using radio frequency (RF) plasma. Fluoropolymers have been extensively used in blood contacting materials, such as blood vessel replacements due to their reduced thrombogenicity and reduced platelet reactivity. The compositions of plasma-treated surfaces were determined by electron spectroscopy for chemical analysis (ESCA). Also, contact angle measurements, cell cytotoxicity and the degradation profile of the treated polymers are presented. Finally, relevant blood compatibility parameters, including plasma protein adsorption, platelet adhesion and morphology, were evaluated. We hypothesized that tight binding of adsorbed albumin by fluoropolymers enhances its potential for blood-contacting applications.

STATEMENT OF SIGNIFICANCE

Although bioresorbable stents made from poly(lactic acid) (PLA) may have long-term clinical advantages, they have shown higher rates of early thrombosis as compared with permanent metallic stents. To improve the thromboresistance of PLA, we developed a novel method for surface fluorination of this polymer with a perfluoro compound. Fluoropolymers (e.g., expanded polytetrafluoroethylene) have long been used in blood-contacting applications due to their satisfactory clinical performance. This is the first report of PLA surface fluorination which might be applied to the fabrication of a new generation of fluorinated PLA stents with improved platelet interaction, tunable degradability and drug release capabilities. Also, we describe a general strategy for improving the platelet interactions with biomaterials based on albumin retention.

Permeability of Ciprofloxacin-Loaded Polymeric Micelles Including Ginsenoside as P-glycoprotein Inhibitor through a Caco-2 Cells Monolayer as an Intestinal Absorption Model

The low oral bioavailability of ciprofloxacin is associated with two distinct challenges: its low aqueous solubility and efflux by p-glycoproteins (P-gp) in the intestinal membrane. Several studies were conducted in order to improve its solubility and permeability through the gastrointestinal membrane. In this study, in a full factorial design study, eight polymeric micelles were prepared and their characteristics, including particle size, loading and release rate were evaluated. Polymeric micelles demonstrated particle sizes below 190 nm and 27⁻88% loading efficiency. Drug release was affected by drug solubility, polymeric micelle erosion and swelling in simulated gastrointestinal fluids. An optimized polymeric micelle was prepared based on appropriate characteristics such as high drug loading and low particle size; and was used for a permeation study on Caco-2 cells. Optimized polymeric micelles with and without ginsenoside and ginsenoside alone enhanced drug permeability through Caco-2 cells significantly in the absorptive direction. The effect of ginsenoside was dose dependent and the maximum effect was seen in 0.23 mg/mL concentration. Results showed that P-gp may not be responsible for ciprofloxacin secretion into the gut. The main mechanism of ciprofloxacin transport through Caco-2 cells in both directions is active diffusion and P-gp has inhibitory effects on ciprofloxacin permeability in the absorptive direction that was blocked by ginsenoside and micelles without ginsenoside.

The emerging role of physiologically based pharmacokinetic modelling in solid drug nanoparticle translation

The use of solid drug nanoparticles (SDN) has become an established approach to improve drug delivery, supporting enhancement of oral absorption and long-acting administration strategies. A broad range of SDNs have been successfully utilised for multiple products and several development programmes are currently underway across different therapeutic areas. With some approaches, a large range of material space is available with diversity in physical characteristics, excipient choice and pharmacological behaviour. The selection of SDN lead candidates is a complex process including a broad range of in vitro and in vivo data, and a better understanding of how physical characteristics relate to performance is required. Physiologically-based pharmacokinetic (PBPK) modelling is based upon a comprehensive integration of experimental data into a mathematical description of drug distribution, allowing simulation of SDN pharmacokinetics that can be qualified in vivo prior to human prediction. This review aims to provide a description of how PBPK can find application into the development of SDN. Integration of predictive PBPK modelling into SDN development allows a better understanding of the SDN dose-response relationship, supporting a framework for rational optimisation while reducing the risk of failure in developing safe and effective nanomedicines.

In vivo release of peptide-loaded PLGA microspheres assessed through deconvolution coupled with mechanistic approach

In this study, a reevaluation of the in vivo release phases from long-release PLGA-based microspheres is presented, leading to a better characterization of the plasma concentrations/time profile. Microspheres were designed for intramuscular injection releasing a cyclic somatostatin analog over 70 days. Clinical study was performed in 64 healthy subjects receiving a subcutaneous dose of an immediate release solution as reference formulation and an intramuscular injection of microspheres as test formulation. The in vivo input curve was obtained by numerical deconvolution. Results showed that double Weibull function could not fit correctly the tri-phasic (burst, lag, and erosion) in vivo input profile typical for PLGA-based formulations, due to a change in the drug release trend in the terminal phase. Triple Weibull showed a significant improvement in the curve fitting, each term being assigned to one of the following phases: initial (burst/lag), erosion, and terminal phase of drug release. The existence of the additional terminal phase was confirmed by a mechanistic approach as well, which denoted that this phase was, most probably, a consequence of the release mechanism change from erosion to diffusion controlled. The same model demonstrated that the burst release was as well influenced by the polymer swelling, while currently existing theories state that the burst phase is mainly determined by the dissolution of immediately available drug substance and diffusion through surface related pores.

Albumin-Assisted Method Allows Assessment of Release of Hydrophobic Drugs From Nanocarriers

Polymeric nanoparticles have been extensively studied as drug delivery vehicles both in vitro and in vivo for the last two decades. In vitro methods to assess drug release profiles usually utilize degradation of nanoparticles in aqueous medium, followed by the measurement of the concentration of the released drug. This method, however, is difficult to use for drugs that are poorly water soluble. In this study, a protocol for measuring drug release kinetic using albumin solution as the medium is described. Albumin is a major blood transport protein, which mediates transport of many lipid soluble compounds including fatty acids, hormones, and bilirubin. The use of a dialysis-based system utilizing albumin dialysate solution allows hydrophobic drug release from a diverse set of drug delivery modalities is demonstrated. The method using liposomes and PLGA nanoparticles as drug carriers, and two model hydrophobic drugs, 17β-estradiol, and dexamethasone is validated.

Sulfanilamide in solution and liposome vesicles; in vitro release and UV-stability studies

The main goal of this study was to develop a liposome formulation with sulfanilamide and to investigate the liposomes impact on its release and stability to the UV-A/UV-B and UV-C irradiation. Liposome dispersions with incorporated sulfanilamide were prepared by thin-film hydration method and liposomes role to the sulfanilamide release was investigated by using a dialysis method. Comparatively, sulfanilamide in phosphate buffer solution was subject to release study as well to the UV irradiation providing for the possibilities of kinetics analysis. In vitro drug release study demonstrated that 20% of sulfanilamide was released from liposomes within 1 h that is approximately twice as slower as in the case of dissolved sulfanilamide in phosphate buffer solution. The kinetic release process can be described by Korsmeyer–Peppas model and according to the value of diffusion release exponent it can be concluded that drug release mechanism is based on the phenomenon of diffusion. The sulfanilamide degradation in phosphate buffer solution and liposomes is related to the formation of UV-induced degradation products that are identified by UHPLC/MS analysis as: sulfanilic acid, aniline and benzidine. The UV-induced sulfanilamide degradation in the phosphate buffer solution and liposome vesicles fits the first- order kinetic model. The degradation rate constants are dependent on the involved UV photons energy input as well as sulfanilamide microenvironment. Liposome microenvironment provides better irradiation sulfanilamide stability. The obtained results suggest that liposomes might be promising carriers for delayed sulfanilamide delivery and may serve as a basis for further research.

Injectable In Situ Forming Depot Systems for Long-Acting Contraception

Up to date, no long-acting reversible contraceptive (LARC) is developed to be injectable through needles smaller than 18 G and can also provide contraception for more than 3 months after single injection. In this study, injectable polymeric in situ forming depot (ISD) systems are developed to have injectability through 21-23 G needles, and capability of sustained release of levonorgestrel (LNG) for at least 7 months in vitro and in vivo after single subcutaneous injection in rats. The systems are polymeric solutions composed of biodegradable poly(lactide-co-glycolide) and poly(lactic acid) polymers dissolved in a mixture of solvents like N-methyl-2-pyrrolidone and benzyl benzoate or triethyl citrate. LNG released from ISD systems successfully suppressed the estrous cycle of rats at plasma concentration above 0.35 ng mL^-1 . At the end of the treatment, when LNG plasma concentration drops down to be nondetectable, predictable return of fertility is observed in rats. The designed ISD systems have great potential to be further developed into robust injectable LARCs that can be injected through a 21 G or smaller needle and achieve a variety of contraception durations with high patient compliance and low cost.

Dual-stimuli responsive injectable microgel/solid drug nanoparticle nanocomposites for release of poorly soluble drugs

An in situ forming implant (ISFI) for drug delivery combines the potential to improve therapeutic adherence for patients with simple administration by injection. Herein, we describe the preparation of an injectable nanocomposite ISFI composed of thermoresponsive poly(N-isopropylacrylamide) based microgels and solid drug nanoparticles. Monodisperse poly(N-isopropylacrylamide) or poly(N-isopropylacrylamide-co-allylamine) microgels were prepared by precipitation polymerisation with mean diameters of approximately 550 nm at 25 °C. Concentrated dispersions of these microgels displayed dual-stimuli responsive behaviour, forming shape persistent bulk aggregates in the presence of both salt (at physiological ionic strength) and at body temperature (above the lower critical solution temperature of the polymer). These dual-stimuli responsive microgels could be injected into an agarose gel tissue mimic leading to rapid aggregation of the particles to form a drug depot. Additionally, the microgel particles aggregated in the presence of other payload nanoparticles (such as dye-containing polystyrene nanoparticles or lopinavir solid drug nanoparticles) to form nanocomposites with high entrapment efficiency of the payload. The resulting microgel and solid drug nanoparticle nanocomposites displayed sustained drug release for at least 120 days, with the rate of release tuned by blending microgels of poly(N-isopropylacrylamide) with poly(N-isopropylacrylamide-co-allylamine) microgels. Cytotoxicity studies revealed that the microgels were not toxic to MDCK-II cells even at high concentrations. Collectively, these results demonstrate a novel, easily injectable, nanocomposite ISFI that provides long-term sustained release for poorly water-soluble drugs without a burst release.

Complexation of oxethazaine with 2-hydroxypropyl-β-cyclodextrin: increased drug solubility, decreased cytotoxicity and analgesia at inflamed tissues

Objectives

Oxethazaine (OXZ) is one of the few local anaesthetics that provides analgesia at low pH, but presents poor solubility, cytotoxicity and no parenteral formulations. To address these issues, we aimed to prepare OXZ host-guest inclusion complex with hydroxypropyl-beta-cyclodextrin (HP-β-CD).

Methods

The inclusion complex was formed by co-solubilization, followed by a job plot analysis to determine stoichiometry of complexation and dialysis equilibrium analysis (based on UV/VIS absorption and fluorescence profiles of OXZ). Complex formation was confirmed by phase-solubility data, X-ray, Scanning Electron Microscopy and DOSY-1H-NMR experiments. In vitro cytotoxicity was analysed by MTT test in 3T3 fibroblasts. In vivo analgesia was tested by Von Frey test (inflammatory wounds – rats).

Key findings

Oxethazaine complexed (1 : 1 molar ratio) with HP-β-CD, as indicated by loss of OZX crystalline structure (X-ray) and strong host: guest interaction (NMR, K = 198/m), besides increased solubility. In vitro cell survival improved with the complex (IC50 OXZ = 28.9 μm, OXZ : HP-β-CD = 57.8 μm). In addition, the complex (0.1% OXZ) promoted in vivo analgesia for the same time that 2% lidocaine/epinephrine did.

Conclusion

Our results show that complexation improved physicochemical and biological properties of OXZ, allowing its application to inflamed tissues by parenteral routes.

An Accelerated Release Study to Evaluate Long-Acting Contraceptive Levonorgestrel-Containing in Situ Forming Depot Systems

Biodegradable polymer-based injectable in situ forming depot (ISD) systems that solidify in the body to form a solid or semisolid reservoir are becoming increasingly attractive as an injectable dosage form for sustained (months to years) parenteral drug delivery. Evaluation of long-term drug release from the ISD systems during the formulation development is laborious and costly. An accelerated release method that can effectively correlate the months to years of long-term release in a short time such as days or weeks is economically needed. However, no such accelerated ISD system release method has been reported in the literature to date. The objective of the current study was to develop a short-term accelerated in vitro release method for contraceptive levonorgestrel (LNG)-containing ISD systems to screen formulations for more than 3-month contraception after a single subcutaneous injection. The LNG-containing ISD formulations were prepared by using biodegradable poly(lactide-co-glycolide) and polylactic acid polymer and solvent mixtures containing N-methyl-2-pyrrolidone and benzyl benzoate or triethyl citrate. Drug release studies were performed under real-time (long-term) conditions (PBS, pH 7.4, 37 °C) and four accelerated (short-term) conditions: (A) PBS, pH 7.4, 50 °C; (B) 25% ethanol in PBS, pH 7.4, 50 °C; (C) 25% ethanol in PBS, 2% Tween 20, pH 7.4, 50 °C; and (D) 25% ethanol in PBS, 2% Tween 20, pH 9, 50 °C. The LNG release profile, including the release mechanism under the accelerated condition D within two weeks, correlated (r² ≥ 0.98) well with that under real-time conditions at four months.

Microbicide vaginal rings: Technological challenges and clinical development

Vaginal rings (VRs) are flexible, torus-shaped, polymeric devices designed to sustain delivery of pharmaceutical drugs to the vagina for clinical benefit. Following first report in a 1970 patent application, several steroid-releasing VR products have since been marketed for use in hormone replacement therapy and contraception. Since 2002, there has been growing interest in the use of VR technology for delivery of drugs that can reduce the risk of sexual acquisition of human immunodeficiency virus type 1 (HIV-1), the causative agent of acquired immunodeficiency syndrome (AIDS). Although no vaginally-administered product has yet been approved for HIV reduction/prevention, extensive research efforts are continuing and a number of VR devices offering sustained release of so-called 'HIV microbicide' compounds are currently being evaluated in late-stage clinical studies. This review article provides an overview of the published scientific literature within this important field of research, focusing primarily on articles published within peer-reviewed journal publications. Many important aspects of microbicide-releasing VR technology are discussed, with a particular emphasis on the technological, manufacturing and clinical challenges that have emerged in recent years.

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.

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.

A miniaturized in vitro release method for investigating drug-release mechanisms

We have evaluated a miniaturized in vitro method, based on the μDISS Profiler™ technique that enables on-line monitoring of drug release from a 21 μl sample with 10 ml of release medium. Four model drugs in eight clinically used formulations, including both solid and non-solid drug delivery systems, were investigated. The acquired data were compared with historical in vitro release data from the same formulations. Use of the Weibull function to describe the in vitro drug-release profiles allowed discrimination between the selected formulations with respect to the drug-release mechanisms. Comparison of the release data from the same formulation in different in vitro set-ups showed that the methodology used can affect the mechanism of in vitro release. We also evaluated the ability of the in vitro methods to predict in vivo activity by comparing simulated plasma concentration-time profiles acquired from the application of the biopharmaceutical software GI-Sim to the in vitro observations. In summary, the simulations based on the miniaturized-method release data predicted the plasma profiles as well as or more accurately than simulations based on the historical release data in 71% of the cases and this miniaturized in vitro method appears to be applicable for both solid and non-solid formulations.

Transdermal nitroglycerin delivery using acrylic matrices: design, formulation, and in vitro characterization

Nitroglycerin (TNG) transdermal drug delivery systems (TDDSs) with different acrylic pressure-sensitive adhesives (PSAs) and chemical permeation enhancers (CPEs) were prepared. The effects of PSAs and CPEs types and concentrations on skin permeation and in vitro drug release from devices were evaluated using the dissolution method as well as the modified-jacketed Franz diffusion cells fitted with excised rat abdominal skin. It was demonstrated that the permeation rate or steady state flux (J_ss) of the drug through the excised rat skin was dependent on the viscosity and type of acrylic PSA as well as the type of CPE. Among different acrylic PSAs, Duro-Tak 2516 and Duro-Tak 2054 showed the highest and Duro-Tak 2051 showed the lowest J_ss. Among the various CPEs, propylene glycol and cetyl alcohol showed the highest and the lowest enhancement of the skin permeation of TNG, respectively. The adhesion properties of devices such as 180° peel strength and probe tack values were obtained. It was shown that increasing the concentration of CPE led to reduction in the adhesion property of PSA. Moreover, after optimization of the formulation, it was found that the use of 10% PG as a CPE and 25% nitroglycerin loading in Duro-Tak 2054 is an effective monolithic DIAP for the development of a transdermal therapeutic system for nitroglycerin.

Development and validation of a discriminative dissolution test for betamethasone sodium phosphate and betamethasone dipropionate intramuscular injectable suspension

The intramuscular administration of the injectable suspension betamethasone sodium phosphate (BSP) and betamethasone dipropionate (BD) has immediate therapeutic activity due to solubilized BSP and prolonged activity resulting from the slow release of BD micro-crystals. The purpose of this study was to develop and validate a dissolution method for BD in intramuscular injectable suspensions with detection by high-performance liquid chromatography (HPLC) method. Five commercial products presented a distribution of particle sizes, ranging between 7.43 and 40.25 μm as measured by laser diffraction. It was also found that particle sizes differed between batches of the same product. The different products were tested using the paddle apparatus, with stirring speeds of 25 and 50 rpm in 300 mL of phosphate buffer; simulated body fluid, muscle fluid, and synovial fluid were used as biorelevant dissolution media at 37±0.5°C. It was verified that not only does average particle size affect the dissolution rate, but also the mode and the polydispersity index of the particles. Discriminatory power was obtained using the in vitro dissolution method with 0.1 M sodium phosphate buffer pH 7.4 containing 0.1% sodium lauryl sulfate and a stirring speed of 50 rpm. The HPLC-method is linear, precise, selective, and accurate for the quantification of BSP and BD in dissolution profile testing. This dissolution method can be utilized as a method to control the quality of these injectable suspensions.