Controlled release implants based on cast lipid blends

Biobased Ionic Liquids as Multitalented Materials in Lipidic Drug Implants

Lipidic implants are valuable controlled delivery systems that present good biocompatibility and are useful for long-lasting therapies. However, these promising systems can present inflexible drug release profiles that limit their performance. Thus, finding new materials to overcome this drawback is crucial. Herein, lipidic implants containing caffeine and poorly soluble salicylic acid and rutin were developed. The inclusion of Gelucire^® 50/02, sucrose, and two biobased ionic liquids, [Cho][Phe] and [Cho][Glu], were evaluated as a mean to improve the performance of the systems. The formulation procedure, dye content distribution, drug content, drug release, water content, and lipidic erosion of the developed systems were assessed. AFM analysis of the implants containing ILs was also performed. The results demonstrated that neither Gelucire^® 50/02 nor sucrose were suitable tools to improve the drug release profile. In contrast, the ILs proved to be promising materials for multiple reasons; not only did they facilitate the formulation and incorporation of the studied drugs into the implants, but they also allowed a more suitable release profile, with [Cho][Glu] allowing a higher drug release due to its ability to increase surface wrinkling. Hence, this study showcases ILs as multitalented materials in lipid-based drug implants.

Mechanisms of water permeation and diffusive API release from stearyl alcohol and glyceryl behenate modified release matrices

This work aims to develop complimentary analytical tools for lipid formulation selection that offer insights into the mechanisms of in-vitro drug release for solid lipid modified release excipients. Such tools are envisioned to aide and expedite the time consuming process of formulation selection and development. Two pharmaceutically relevant solid lipid excipients are investigated, stearyl alcohol and glyceryl behenate, which are generally known to exhibit faster and slower relative release rates, respectively. Nuclear magnetic resonance spectroscopy and diffusometry are used, along with water uptake and dissolution experiments to help distinguish between two proposed in-vitro release mechanisms for crystalline caffeine from these matrices: 1) rate limiting movement of the wetting front through the particle, and 2) rate limiting diffusive release of the active from the wetted particle. Findings based on water permeation rates, API diffusion coefficients and kinetic modeling suggest that the rate limiting steps for caffeine release from these matrices are different, with stearyl alcohol being co-rate limited by movement of the wetting front and diffusive release of API, whereas glyceryl behenate is more strictly limited by diffusive release of API from the wetted matrix. A Peclet-like number is proposed to describe the different regimes of rate limitation for drug release. NMR spectroscopy and diffusometry are demonstrated to be useful tools for elucidating mechanisms of API release from crystalline drug/lipid mixtures and have significant potential value as screening tools in MR formulation development.

Investigation on Secondary Structure Alterations of Protein Drugs as an Indicator of Their Biological Activity Upon Thermal Exposure

Protein drugs are important therapeutic agents however; they may degrade during formulation processing. The objective of this study was to investigate the correlation between secondary structure alterations and the retentions of biological activity of protein upon the application of thermal stress. Catalase, horseradish peroxidase and α- chymotrypsin were employed as model proteins. Each protein was heated in a solid and solution state at a temperature of 70 °C for 1 h. Attenuated total reflectance Fourier transform infrared spectroscopy, size-exclusion chromatography and biological activity assay were performed. Results showed that heat-exposure of protein solids at 70 °C caused minimum changes in secondary structure and biological activity was almost retained. However, thermal exposure of protein aqueous solution induced significant changes in the secondary structure indicated by area overlap values and caused considerable reduction in the biological activity. The changes in secondary structures were found to be in full alignment with the loss of biological activity for both protein solids as well as aqueous solutions. Catalase lost entire biological activity upon heating in the solution state. In conclusion, the findings of the present study indicate a direct correlation between protein secondary structure alterations and the retention of biological activity which can be taken into account during the development and delivery of protein drugs formulations.

Attenuated Total Reflection Fourier Transform Infrared (ATR FT-IR) Spectroscopy as an Analytical Method to Investigate the Secondary Structure of a Model Protein Embedded in Solid Lipid Matrices

Protein drugs may encounter conformational perturbations during the formulation processing of lipid-based solid dosage forms. In aqueous protein solutions, attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy can investigate these conformational changes following the subtraction of spectral interference of solvent with protein amide I bands. However, in solid dosage forms, the possible spectral contribution of lipid carriers to protein amide I band may be an obstacle to determine conformational alterations. The objective of this study was to develop an ATR FT-IR spectroscopic method for the analysis of protein secondary structure embedded in solid lipid matrices. Bovine serum albumin (BSA) was chosen as a model protein, while Precirol AT05 (glycerol palmitostearate, melting point 58 ℃) was employed as the model lipid matrix. Bovine serum albumin was incorporated into lipid using physical mixing, melting and mixing, or wet granulation mixing methods. Attenuated total reflection FT-IR spectroscopy and size exclusion chromatography (SEC) were performed for the analysis of BSA secondary structure and its dissolution in aqueous media, respectively. The results showed significant interference of Precirol ATO5 with BSA amide I band which was subtracted up to 90% w/w lipid content to analyze BSA secondary structure. In addition, ATR FT-IR spectroscopy also detected thermally denatured BSA solid alone and in the presence of lipid matrix indicating its suitability for the detection of denatured protein solids in lipid matrices. Despite being in the solid state, conformational changes occurred to BSA upon incorporation into solid lipid matrices. However, the extent of these conformational alterations was found to be dependent on the mixing method employed as indicated by area overlap calculations. For instance, the melting and mixing method imparted negligible effect on BSA secondary structure, whereas the wet granulation mixing method promoted more changes. Size exclusion chromatography analysis depicted the complete dissolution of BSA in the aqueous media employed in the wet granulation method. In conclusion, an ATR FT-IR spectroscopic method was successfully developed to investigate BSA secondary structure in solid lipid matrices following the subtraction of lipid spectral interference. The ATR FT-IR spectroscopy could further be applied to investigate the secondary structure perturbations of therapeutic proteins during their formulation development.

Investigation on Secondary Structure Perturbations of Proteins Embedded in Solid Lipid Matrices as a Novel Indicator of their Biological Activity upon In Vitro Release

Protein biologics are prone to conformational changes during formulation development. Limited methods are available for conformational analysis of proteins in solid state and in the presences of formulation excipients. The aim of this study was to investigate the secondary structures of proteins encased in solid lipid matrices as a novel indicator of their stability upon in vitro release. Model proteins namely catalase and lysozyme were incorporated into lipid namely Precirol® AT05 (glycerol palmitostearate, melting point 58°C) at 30% w/w loading using melting and mixing and wet granulation methods. Attenuated total reflectance (ATR-FTIR) spectroscopy, size-exclusion chromatography (SEC) and biological activity analyses were performed. The information about secondary structure was acquired using second derivative analysis of amide-I band (1600-1700 cm^-1). ATR analysis demonstrated interference of lipid spectrum with protein amide-I band which was subsequently subtracted to allow the analysis of the secondary structure. ATR spectra amide-I bands showed shifts peak band positions compared to native protein for matrices prepared using wet granulation. SEC analysis gave evidence of protein aggregation for catalase which was increased using wet granulation. The biological activity of catalase was statistically different from that of control and was affected by the incorporation method and was found to be in alignment with ATR spectral changes and extent of aggregation. In conclusion, ATR spectroscopy could analyze protein secondary structure in lipid matrices provided lipid interference was minimized. The ATR spectral changes and formation of aggregates can indicate the loss in biological activity of protein released from solid lipid matrices.

Solvent-free melting techniques for the preparation of lipid-based solid oral formulations

Lipid excipients are applied for numerous purposes such as taste masking, controlled release, improvement of swallowability and moisture protection. Several melting techniques have evolved in the last decades. Common examples are melt coating, melt granulation and melt extrusion. The required equipment ranges from ordinary glass beakers for lab scale up to large machines such as fluid bed coaters, spray dryers or extruders. This allows for upscaling to pilot or production scale. Solvent free melt processing provides a cost-effective, time-saving and eco-friendly method for the food and pharmaceutical industries. This review intends to give a critical overview of the published literature on experiences, formulations and challenges and to show possibilities for future developments in this promising field. Moreover, it should serve as a guide for selecting the best excipients and manufacturing techniques for the development of a product with specific properties using solvent free melt processing.

Lipid-based intravesical drug delivery systems with controlled release of trospium chloride for the urinary bladder

The overactive bladder (OAB) is a common disease with an overactivity of the detrusor muscle in the bladder wall. Besides peroral administration of anticholinergic drugs and bladder irrigations, there is a need for a sustained release formulation in the urinary bladder. In order to realise a local long-term treatment of the overactive urinary bladder, lipidic drug delivery systems were prepared. Requirements for an intravesical application are a long-term controlled release of trospium chloride, a high drug loading and small sized drug carriers to permit an insertion through the urethra into the urinary bladder. The drug delivery systems were manufactured by using compression (mini-tablets), solid lipid extrusion (extrudates) and a melting and casting technique (mini-moulds) with different amounts of trospium chloride and glyceryl tristearate as matrix former. Drug release depended on the drug loading and the preparation method. Mini-tablets and lipidic extrudates showed a drug release over five days, whereas that from mini-moulds was negligibly small. The appearance of polymorphic transformations during processing and storage was investigated by using differential scanning calorimetry and X-ray diffraction. In contrast to mini-tablets and mini-moulds, lipidic extrudates showed no polymorphic transformations. In summary, lipids are suitable matrix formers for a highly water-soluble drug, like trospium chloride. Despite a drug loading of up to 30%, it was feasible to achieve a drug release ranging from several days up to weeks. In addition, small dosage forms with a size of only a few millimetres were realised. Therefore, an insertion and excretion through the urethra is possible and the requirements for an intravesical application are fulfilled.

MALDI-TOF MS imaging of controlled release implants

MALDI-TOF MS (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry) imaging is used to characterize novel lipid implants allowing for controlled drug delivery. Importantly, this innovative technique provides crucial information on the inner structure of the implants before and after exposure to the release medium and does not require the addition of marker substances. Implants were prepared by extrusion at room temperature. Thus, in contrast to hot-melt extruded systems, the risks of drug inactivation and solid state transformations of the lipid matrix former are reduced. Hydrogenated/hardened soybean oil and glyceryl tristearate were studied as lipids and propranolol hydrochloride and theophylline as drugs, exhibiting significantly different solubility in water. The implants were also characterized by optical microscopy, differential scanning calorimetry, water uptake and lipid erosion studies, mathematical modeling as well as in vitro drug release measurements. Importantly, broad spectra of drug release patterns with release periods ranging from a few days up to several months could easily be provided when varying the initial drug content and type of lipid, irrespective of the type of drug. The diameter of the implants can be as small as 1mm, facilitating injection. MALDI-TOF MS imaging revealed homogeneous macroscopic drug distributions within the systems, but steep drug concentration gradients in radial and axial direction at the lower micrometer level, indicating drug- and lipid-rich domains. As the implants do not significantly swell, local irritation upon administration due to mechanical stress can be expected to be limited. Good agreement between experimentally measured and theoretically calculated drug release kinetics revealed that diffusional mass transport plays a major role for the control of drug release from this type of advanced drug delivery systems.

Predictability of drug release from cochlear implants

A simplified mathematical theory is presented allowing for in silico simulation of the effects of key parameters of miniaturized implants (size and composition) on the resulting drug release kinetics. Such devices offer a great potential, especially for local drug treatments, e.g. of the inner ear. However, the preparation and characterization of these systems is highly challenging, due to the small system dimensions. The presented mathematical theory is based on Fick's second law of diffusion. Importantly, theoretical predictions do not require the knowledge of many system-specific parameters: Only the "apparent" diffusion coefficient of the drug within the implant matrix is needed. This parameter can be easily determined via drug release measurements from thin, macroscopic films. The validity of the theoretical model predictions was evaluated by comparison with experimental results obtained with a cochlear implant. The latter consisted of miniaturized electrodes, which were embedded in a silicone matrix loaded with various amounts of dexamethasone. Importantly, independent experimental results confirmed the theoretical predictions. Thus, the presented simplified theory can help to significantly speed up the optimization of this type of controlled drug delivery systems, especially if long release periods are targeted (e.g., several months or years). Straightforward experiments with thin, macroscopic films and computer simulations can allow for rapid identification of optimal system design.