Characterization of the solubility and dissolution properties of several new rifampicin polymorphs, solvates, and hydrates

Assessing Polymorphic Purity of Rifampicin in Double and Triple-Drug Fixed-Dose Combination Products

First-line tuberculostatic agents, Rifampicin (RIF), Isoniazid (ISH), Ethambutol (ETB), and Pyrazinamide (PZA) are generally administered as a fixed-dose combination (FDC) for improving patient adherence. The major quality challenge of these FDC products is their variable bioavailability, where RIF and its solid state are key factors. In this work, the analysis of the impact of the polymorphism in the performance of RIF in RIF-ISH and PZA-RIF-ISH combined products was carried out by an overall approach that included the development and validation of two methodologies combining near-infrared (NIR) spectroscopy and partial least squares (PLS) to the further evaluation of commercial products. For NIR-PLS methods, training and validation sets were prepared with mixtures of Form I/Form II of RIF, and the appropriate amount of ISH (for double associations) or ISH-PZA (for triple associations). The corresponding matrix of the excipients was added to the mixture of APIs to simulate the environment of each FDC product. Four PLS factors, reduced spectral range, and the combination of standard normal variate and Savitzky-Golay 1st derivative (SNV-D') were selected as optimum data pre-treatment for both methods, yielding satisfactory recoveries during the analysis of validation sets (98.5±2.0%, and 98.7±1.8% for double- and triple-FDC products, respectively). The NIR-PLS model for RIF-ISH successfully estimated the polymorphic purity of Form II in double-FDC capsules (1.02 ± 0.02w/w). On the other hand, the NIR-PLS model for RIF-ISH-PZA detected a low purity of Form II in triple FDC tablets (0.800 ± 0.021w/w), these results were confirmed by X-ray powder diffraction. Nevertheless, the triple-FDC tablets showed good performance in the dissolution test (Q=99-102%), implying a Form II purity about of 80% is not low enough to affect the safety and efficacy of the product.

Preparation and Characterization of a Rifampicin Coamorphous Material with Tromethamine Coformer: An Experimental-Theoretical Study

Rifampicin (RIF) is an antibiotic used to treat tuberculosis and leprosy. Even though RIF is a market-available drug, it has a low aqueous solubility, hindering its bioavailability. Among the strategies for bioavailability improvement of poorly soluble drugs, coamorphous systems have been revealed as an alternative in the increase of the aqueous solubility of drug systems and at the same time also increasing the amorphous state stability and dissolution rate when compared with the neat drug. In this work, a new coamorphous form from RIF and tromethamine (TRIS) was synthesized by slow evaporation. Structural, electronic, and thermodynamic properties and solvation effects, as well as drug-coformer intermolecular interactions, were studied through density functional theory (DFT) calculations. Powder X-ray diffraction (PXRD) data allowed us to verify the formation of a new coamorphous. In addition, the DFT study indicates a possible intermolecular interaction by hydrogen bonds between the available amino and carbonyl groups of RIF and the hydroxyl and amino groups of TRIS. The theoretical spectra obtained are in good agreement with the experimental data, suggesting the main interactions occurring in the formation of the coamorphous system. PXRD was used to study the physical stability of the coamorphous system under accelerated ICH conditions (40 °C and 75% RH), indicating that the material remained in an amorphous state up to 180 days. The thermogravimetry result of this material showed a good thermal stability up to 153 °C, and differential scanning calorimetry showed that the glass temperature (Tg) was at 70.0 °C. Solubility studies demonstrated an increase in the solubility of RIF by 5.5-fold when compared with its crystalline counterpart. Therefore, this new material presents critical parameters that can be considered in the development of new coamorphous formulations.

Physicochemical interaction of rifampicin and ritonavir-lopinavir solid dispersion: an in-vitro and ex-vivo investigation

OBJECTIVE

To investigate the in-situ physicochemical interaction of Rifampicin and Ritonavir - Lopinavir Solid dispersion administered for the treatment of comorbid conditions i.e. Tuberculosis and HIV/AIDS.

METHODS

pH-shift dissolution of Rifampicin (RIF) in presence of Ritonavir-Lopinavir solid dispersion (RL-SD) was carried out in USP phosphate buffer 6.8 and FaSSIF. Equilibrium and amorphous solubility were determined for the drugs. Pure drugs, their physical mixtures, and pH-shifted co-precipitated samples were characterized using DSC, PXRD, and FTIR. Fluorescence spectroscopy was used to investigate drug-rich and drug-lean phases. In-vitro and ex-vivo flux studies were also carried out.

RESULTS

The results showed significant differences in the solubility and dissolution profiles of RTV and LOP in the presence of RIF, while RIF profile remained unchanged. Amorphicity, intermolecular interaction and aggregate formation in pH-shifted samples were revealed in DSC, XRD and FTIR analysis. Fluorescence spectroscopy confirmed the formation of drug-rich phase upon pH-shift. In-vitro and ex-vivo flux studies revealed significant reduction in the flux of all the drugs when studied in presence of second drug.

CONCLUSION

RIF, RTV and LOP in presence of each other on pH-shift, results in co-precipitation in the amorphous form (miscible) which leads to reduction in the highest attainable degree of supersaturation. This reduction corresponds to the mole fraction of the RIF, RTV and LOP within the studied system. These findings suggest that the concomitant administration of these drugs may lead to physicochemical interactions and possible ineffective therapy.

Spectroscopy and dynamics of beta-lactoglobulin complexed with rifampicin

In this paper, we report the binding interaction of milk protein, beta-lactoglobulin (BLG), with an antibiotic against tuberculosis, rifampicin (RIF). BLG intrinsic fluorescence from tryptophan (Trp) amino acids was monitored to understand protein-drug interactions. Binding parameters and stoichiometry were estimated with the help of fluorescence spectral changes. Synchronous fluorescence spectroscopy was employed to exclusively monitor the Trp and Tyrosine (Tyr) environment in the presence of RIF. With the help of steady state fluorescence at different temperatures supported by time-resolved fluorescence, we confirmed that the protein forms a static complex with RIF. Thermodynamic parameters, ΔH and ΔS values, showed the involvement of hydrophobic forces between the RIF and BLG. Competitive displacement assay with ANS confirmed the BLG calyx as the binding site for RIF. Energy transfer mechanism from Trp to RIF was attributed to the fluorescence changes in protein upon complexation. The Förster resonance energy transfer (FRET) was used to find distance, energy transfer efficiency and rate of energy transfer between donor (BLG) and acceptor (RIF). Fourier-transform infrared (FTIR) spectroscopy was utilized for estimating changes in the secondary structure of BLG induced by RIF. Molecular docking was used to visualise the binding location of RIF on BLG. Molecular dynamics (MD) simulation studies showed a consistent binding interactions between BLG and RIF during the 100 ns simulation period and this well supported the increased beta sheet content in FTIR. Overall our results establish the potential of intrinsic fluorescence of BLG in combination with biophysical tools to rationalize drug-protein interactions.Communicated by Ramaswamy H. Sarma.

Antibody-Functionalized Polymer Nanoparticles for Targeted Antibiotic Delivery in Models of Pathogenic Bacteria Infecting Human Macrophages

The efficacy of antibody-functionalized poly(d,l-lactide-co-glycolide) (PLGA) nanoparticles (NPs), prepared by nanoprecipitation, carrying rifampicin (RIF) against planktonic, sessile, and intracellular Staphylococcus aureus and Escherichia coli is reported here. A biotinylated anti-S. aureus polyclonal antibody, which binds to structural antigens of the whole bacterium, was functionalized on the surface of RIF-loaded PLGA-based NPs by using the high-affinity avidin-biotin complex. This general strategy allows the binding of commercially available biotinylated antibodies. Coculture models of S. aureus ATCC 25923 and Escherichia coli S17 were used to demonstrate the preferential selectivity of the antibody-functionalized NPs against the Gram-positive bacterium only. At 0.2 μg/mL, complete S. aureus eradication was observed for the antibody-functionalized RIF-loaded NPs, whereas only a 5-log reduction was observed for the nontargeted RIF-loaded NPs. S. aureus is a commensal facultative pathogen having part of its live cycle intracellularly in both phagocytic and nonphagocytic cells. Those intracellular bacterial persisters, named small colony variants, have been postulated as reservoirs of relapsed episodes of infection and consequent treatment failure. At 0.5 μg/mL, the RIF-loaded NPs reduced in 2-log intracellular S. aureus-infecting human macrophages. The ability of those antibody-functionalized nanoparticles to prevent biofilm formation or to reduce the bacterial burden in already-formed mature biofilms is also reported here using S. aureus and E. coli single and cocultured biofilms. In the prevention of S. aureus biofilm formation, the antibody-functionalized NPs exerted a superior inhibition of bacterial growth (up to 2 logs) compared to the nonfunctionalized ones. This study demonstrates the selectivity of the synthesized immunonanoparticles and their antimicrobial efficacy in different scenarios, including planktonic cultures, sessile conditions, and even against intracellular infective pathogens.

In vitro, in-vivo, and in-silico investigation of physicochemical interactions between pioglitazone and rifampicin

There is a possibility of in-situ physicochemical interactions between concomitantly administered drugs. This study aimed to investigate such physicochemical interactions between pioglitazone and rifampicin. Pioglitazone exhibited significantly higher dissolution in the presence of rifampicin, while the dissolution of rifampicin remained unaffected. The solid-state characterization of precipitates recovered after pH-shift dissolution experiments revealed the conversion of pioglitazone into an amorphous form in the presence of rifampicin. The Density Function Theory (DFT) calculations showed the intermolecular hydrogen bonding between rifampicin and pioglitazone. In-situ conversion of pioglitazone in amorphous form and subsequent supersaturation of GIT milieu translated into significantly higher in-vivo exposure of pioglitazone and its metabolites (M-III and M-IV) in Wistar rats. Therefore, it is advisable to consider the possibility of physicochemical interactions between concomitantly administered drugs. Our findings may be beneficial in tailoring the dose of concomitantly administered drugs, particularly for chronic conditions that entail polypharmacy.

A facile one-step jet-millingapproach for the preparation of proliposomal dry powder for inhalationaseffective delivery system for anti-TBtherapeutics

Objective: Physicochemical characterization and assessmentof aerosol dispersion performance of anti-TB proliposome dry powders for inhalation (DPIs) prepared using a single-step jet-milling (JM) approach. Significance: Conventional tuberculosis treatment involves isoniazid and rifampicin as first-line agents in extended oral multi-drug regimes. Liposomal DPIs are emerging as promising alternatives for targeted delivery of anti-TB agents to alveolar macrophages harboring Mycobacterium tuberculosis. However, traditional approaches for liposomal DPI preparation are tedious, time consuming and require sophisticated/expensive equipment. The proposed JM technique for preparation of proliposome DPIs could obviate these limitations and facilitate use of these drugs for more effective and safer treatment. Methods: Proliposome DPIs containing isoniazid and/or rifampicin, cholesterol and cholesterol sulfate were successfully prepared via JM (injection pressure, 7.4 bar; milling pressure, 3.68 bar). Their physicochemical, content uniformity, and in vitro aerosol dispersion performance were assessed using scanning electron microscopy/energy-dispersive X-ray spectroscopy, transmission electron microscopy, dynamic light scattering/Zeta potential, X-ray diffraction spectroscopy, thermogravimetric analysis, high performance liquid chromatography, and the Next Generation Impactor. Results: The DPIs exhibited consistent, spherically shaped, smooth particles. Drug particles were evenly distributed with acceptable content uniformity. Drug crystallinity was not significantly affected by milling and the formulations had minimal (<2.0%) water content. After reconstitution of theDPIs, the hydrodynamic size was about 370.9 - 556.2nm and charge was-12.3 - -47.3mV. Furthermore, the proliposome DPIs presented emitted dose (69.04 - 89.03%), fine particle fraction,< 4.4 µm (13.7 - 57.8%), and mass median aerodynamic diameter (<3.0 µm), which satisfied the requirements for deep lung delivery. Conclusion: The proposed approach was suitable for preparation of proliposome DPIs that could be deployed for local targeting of the lower respiratory tract for treatment of tuberculosis.

Solid state of inhalable high dose powders

High dose inhaled powders have received increased attention for treating lung infections. These powders can be prepared using techniques such as spray drying, spray-freeze drying, crystallization, and milling. The selected preparation technique is known to influence the solid state of the powders, which in turn can potentially modulate aerosolization and aerosolization stability. This review focuses on how and to what extent the change in solid state of high dose powders can influence aerosolization. It also discusses the commonly used solid state characterization techniques and the application of potential strategies to improve the physical and chemical stability of the amorphous powders for high dose delivery.

Development of a Pediatric Relative Bioavailability/Bioequivalence Database and Identification of Putative Risk Factors Associated With Evaluation of Pediatric Oral Products

Generally, bioequivalence (BE) studies of drug products for pediatric patients are conducted in adults due to ethical reasons. Given the lack of direct BE assessment in pediatric populations, the aim of this work is to develop a database of BE and relative bioavailability (relative BA) studies conducted in pediatric populations and to enable the identification of risk factors associated with certain drug substances or products that may lead to failed BE or different pharmacokinetic (PK) parameters in relative BA studies in pediatrics. A literature search from 1965 to 2020 was conducted in PubMed, Cochrane Library, and Google Scholar to identify BE studies conducted in pediatric populations and relative BA studies conducted in pediatric populations. Overall, 79 studies covering 37 active pharmaceutical ingredients (APIs) were included in the database: 4 bioequivalence studies with data that passed BE evaluations; 2 studies showed bioinequivalence results; 34 relative BA studies showing comparable PK parameters, and 39 relative BA studies showing differences in PK parameters between test and reference products. Based on the above studies, common putative risk factors associated with differences in relative bioavailability (DRBA) in pediatric populations include age-related absorption effects, high inter-individual variability, and poor study design. A database containing 79 clinical studies on BE or relative BA in pediatrics has been developed. Putative risk factors associated with DRBA in pediatric populations are summarized.

Experimental Solubility, Thermodynamic/Computational Validations, and GastroPlus-Based In Silico Prediction for Subcutaneous Delivery of Rifampicin

We focused to explore a suitable solvent for rifampicin (RIF) recommended for subcutaneous (sub-Q) delivery [ethylene glycol (EG), propylene glycol (PG), tween 20, polyethylene glycol-400 (PEG400), oleic acid (OA), N-methyl-2-pyrrolidone (NMP), cremophor-EL (CEL), ethyl oleate (EO), methanol, and glycerol] followed by computational validations and in-silico prediction using GastroPlus. The experimental solubility was conducted over temperature ranges T = 298.2-318.2 K) and fixed pressure (p = 0.1 MPa) followed by validation employing computational models (Apelblat, and van't Hoff). Moreover, the HSPiP solubility software provided the Hansen solubility parameters. At T = 318.2K, the estimated maximum solubility (in term of mole fraction) values of the drug were in order of NMP (11.9 × 10^-2) ˃ methanol (6.8 × 10^-2) ˃ PEG400 (4.8 × 10^-2) ˃ tween 20 (3.4 × 10^-2). The drug dissolution was endothermic process and entropy driven as evident from "apparent thermodynamic analysis". The activity coefficients confirmed facilitated RIF-NMP interactions for increased solubility among them. Eventually, GastroPlus predicted the impact of critical input parameters on major pharmacokinetics responses after sub-Q delivery as compared to oral delivery. Thus, NMP may be the best solvent for sub-Q delivery of RIF to treat skin tuberculosis (local and systemic) and cutaneous related disease at explored concentration.

Pharmacokinetics of rifampicin after repeated intra-tracheal administration of amorphous and crystalline powder formulations to Sprague Dawley rats

Rifampicin is one of the key drugs used to treat tuberculosis and is currently used orally. The use of higher oral doses of rifampicin is desired for better therapeutic efficacy, but this is accompanied by increased risk of systemic toxicity thus limiting its recommended oral dose to 10 mg/kg per day. Inhaled delivery of rifampicin is a potential alternative mode of delivery, to achieve high drug concentrations in both the lung and potentially the systemic circulation. In addition, rifampicin exists either as amorphous or crystalline particles, which may show different pharmacokinetic behaviour. However, disposition behaviour of amorphous and crystalline rifampicin formulations after inhaled high-dose delivery is unknown. In this study, rifampicin pharmacokinetics after intra-tracheal administration of carrier-free, amorphous and crystalline powder formulations to Sprague Dawley rats were evaluated. The formulations were administered once daily for seven days by oral, intra-tracheal and oral plus intra-tracheal delivery, and the pharmacokinetics were studied on day 0 and day 6. Intra-tracheal administration of the amorphous formulation resulted in a higher area under the plasma concentration curve (AUC) compared to the crystalline formulation. For both formulations, the intra-tracheal delivery led to significantly higher AUC compared to the oral delivery at the same dose suggesting higher rifampicin bioavailability from the inhaled route. Increasing the intra-tracheal dose resulted in a more than dose proportional AUC suggesting non-linear pharmacokinetics of rifampicin from the inhaled route. Upon repeated administration for seven days, no significant decrease in the AUCs were observed suggesting the absence of rifampicin induced enzyme auto-induction in this study. The present study suggests an advantage of inhaled delivery of rifampicin in achieving higher drug bioavailability compared to the oral route.

(Solvato-) polymorphism of formulations of rifampicin for pulmonary drug delivery prepared using a crystallization/spray drying process

Rifampicin is an antibiotic used in tuberculosis therapy showing extensive (solvato-) polymorphism. Per oral administration of high doses is recommended, but application as dry powder for inhalation at the site of infection being the lungs, is desirable. Recrystallization from ethanol and consecutive spray drying is reported to yield a rifampicin dihydrate with suitable aerosol performance and stability. Nevertheless, the origin of water in the crystal remained unclear and demanded further investigation so to clarify its solid state throughout manufacture and storage. The present study reports the relationship of (solvato-) polymorphs occurring during manufacture and storage of samples recrystallized and spray dried from ethanol, methanol and water and it was concluded that processes involving a recrystallization from EtOH and MeOH produce particles of a common isostructural group of channel solvates. Samples recrystallized and spray dried from water were identified as members of another isostructural group, which was already characterized in literature. As a second aim, aerosol performance and storage stability of the formulations were investigated and all samples showed stable aerosol performance. Chemical stability of samples spray dried from ethanol was found suitable over a period of six months, whereas samples spray dried from methanol or water showed significant degradation.

A study on polymorphic forms of rifampicin for inhaled high dose delivery in tuberculosis treatment

Rifampicin is a first-line, highly effective drug currently used orally as a part of a lengthy multi-drug regimen against tuberculosis (TB). Despite the potential of inhaled therapy as an effective approach for TB treatment, an inhalable formulation of rifampicin has not yet been developed for clinical use. In order to do so, it is necessary to evaluate its solid-state properties, which regulate important characteristics like solubility, dissolution, aerosolization, stability and bioavailability. In this study, a crystallization technique and spray drying were used to prepare inhalable rifampicin formulations. Spray drying yielded amorphous formulation of rifampicin while crystalline dihydrate and pentahydrate formulations were obtained by crystallization. The powders were evaluated for their solid-state properties, in vitro aerosolization and aerosolization stability for three months when stored at different relative humidity conditions. All formulations had a mean particle size smaller than 3.8 µm and had a fine particle fraction (FPF) higher than 58.0%. Amorphous and crystalline dihydrate formulations showed no change in aerosolization parameters (emitted dose and FPF) upon storage for three months. The amorphous and pentahydrate formulations were found to undergo oxidative degradation upon storage, and a decrease in their drug content was observed. Among the formulations prepared, rifampicin dihydrate formulation showed the least degradation over the three months period. The inhalable rifampicin formulations prepared in this study, being excipient free, have the potential to be delivered as inhaled dry powder high-dose rifampicin to the lungs for effective treatment of TB.

Obtaining and Applying Nanohybrid Palygorskite-Rifampicin in the pH-Responsive Release of the Tuberculostatic Drug

Despite having good efficacy in the treatment and prevention of tuberculosis, the administration of rifampicin (RIF) can cause serious side effects, resulting from the prolonged use of this substance. Thus, it is necessary to seek new systems for administering tuberculostatic drugs, to avoid unwanted adverse effects, increase their bioavailability and, consequently, improve their therapeutic efficacy. The present work describes the achievement of a pH-responsive system for RIF, using palygorskite, a fibrous clay mineral, as a nanocarrier. To evaluate the influence of some operational variables on the drug adsorption process, a 2⁴ factorial experimental design was used. The experiment using a maximum concentration (0.125 mg/mL), lower mass of PAL (300 mg), and lower pH (pH 2) was more efficient compared to other experiments, resulting in a higher dose of the incorporated drug, equivalent to 33.62 mg/g. To elucidate the mechanism of interaction between the materials, the hybrid obtained was characterized by different characterization techniques (Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetry/derived thermogravimetry, zeta potential, scanning electron microscopy, and dispersive energy spectroscopy). In addition, kinetic models and adsorption isotherms were applied to the experimental data. Through in vitro release studies, it was possible to verify the effectiveness of the pH-dependent system obtained. The adjustment of experimental release data to the theoretical model of Higuchi indicated that the release of rifampicin occurs in a prolonged way from the palygorskite.

Hot stage microscopy and its applications in pharmaceutical characterization

Hot stage microscopy (HSM) is a thermal analysis technique that combines the best properties of thermal analysis and microscopy. HSM is rapidly gaining interest in pharmaceuticals as well as in other fields as a regular characterization technique. In pharmaceuticals HSM is used to support differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA) observations and to detect small changes in the sample that may be missed by DSC and TGA during a thermal experiment. Study of various physical and chemical properties such sample morphology, crystalline nature, polymorphism, desolvation, miscibility, melting, solid state transitions and incompatibility between various pharmaceutical compounds can be carried out using HSM. HSM is also widely used to screen cocrystals, excipients and polymers for solid dispersions. With the advancements in research methodologies, it is now possible to use HSM in conjunction with other characterization techniques such as Fourier transform infrared spectroscopy (FTIR), DSC, Raman spectroscopy, scanning electron microscopy (SEM) which may have additional benefits over traditional characterization techniques for rapid and comprehensive solid state characterization.

Inhalable dry powders of rifampicin highlighting potential and drawbacks in formulation development for experimental tuberculosis aerosol therapy

Introduction: Recently, tuberculosis was reported as the leading cause of death from a single infectious agent. Standard therapy includes administration of four first-line antibiotics, i.e. rifampicin, isoniazid, ethambutol, and pyrazinamide over a period of at least 26 weeks, which in case of rifampicin oftentimes is accompanied by unwanted side effects and variable bioavailability that compromise a positive therapeutic outcome. As the main site of infection is the lungs, it is desirable to develop a therapeutic formulation to be administered via the pulmonary route.Areas covered: This work presents a literature review on studies investigating inhalable dry powder formulations including rifampicin in the context of an experimental tuberculosis therapy, with a special focus on aerosol performance.Expert opinion: It was found that formulation approaches involving different strategies and functional excipients are under investigation but as of now, no formulation has managed to leap into commercial clinical testing. Reasons for this might not primarily be associated with a lack of suitable candidates, but amongst others a lack of suitable in vitro models to assess the efficacy, therapeutic benefit, and cost-effectiveness of the candidate formulations.

Synthesis and characterization of antibacterial drug loaded β-tricalcium phosphate powders for bone engineering applications

Powders of β-tricalcium phosphate [β-TCP, β-Ca₃(PO₄)₂] and composite powders of β-TCP and polyvinyl alcohol (PVA) were synthesized by using wet precipitation methods. First, the conditions for the preparation of single phase β-TCP have been delineated. In the co-precipitation procedure, calcium nitrate and diammonium hydrogen phosphate were used as calcium and phosphorous precursors, respectively. The pH of the system was varied in the range 7-11 by adding designed amounts of ammonia solution. The filtered cakes were desiccated at 80 °C and subsequently calcined at different temperatures in the range between 700-1100 °C. Later on, rifampicin form II was used to produce drug-loaded β-TCP and PVA/β-TCP powders. All the synthesized materials have been characterized from morphological (by scanning electron microscopy) and structural-chemical (by X-ray diffraction and Fourier transform infrared spectroscopy) point of view. The drug loading capacity of the selected pure β-TCP powder has been assessed. The biological performance (cytocompatibility in fibroblast cell culture and antibacterial efficacy against Escherichia coli and Staphylococcus aureus) has been tested with promising results. Application perspectives of the designed drug-bioceramic-polymer blends are advanced and discussed.

Discovery of new polymorphs of the tuberculosis drug isoniazid

Two new metastable polymorphs of the tuberculosis drug isoniazid, considered monomorphic for sixty years, were discovered using melt crystallization and nanoscale confinement.

Determining the kinetics of desolvation of a TNT/aniline solvate

The kinetic desolvation process of TNT/aniline solvates was investigated using various experimental techniques.

Cryochemically Obtained Nanoforms of Antimicrobial Drug Substance Dioxidine and Their Physico-chemical and Structural Properties

Nanoforms of the antimicrobial drug substance 2,3-bis-(hydroxymethyl) quinoxaline-N,N′-dioxide with particles sizes between 50 and 300 nm were obtained by cryochemical modification of the initial pharmaceutical substance using a freeze-drying technique and were characterized by different physicochemical methods (FTIR, UV-Vis, 1H-NMR, DSC, TG and X-ray diffraction) and transmission electron microscopy (TEM). The data obtained from FTIR- and UV–Vis-spectroscopy confirmed the unaltered chemical structure of dioxidine molecules due to the cryochemical modification method. At the same time, X-ray diffraction and thermal analysis data show the change of the crystal structure compared to the parameters of the initial pharmaceutical dioxidine substance. A higher dissolution rate was revealed for cryomodified dioxidine nanoforms. The existence of three polymorphic crystal phases was established for cryomodified dioxidine samples possessed by some thermal activation processes: two anhydrous polymorphic phases, triclinic (T) and monoclinic (M), and one hydrated form (H).

In Situ Monitoring and Modeling of the Solution-Mediated Polymorphic Transformation of Rifampicin: From Form II to Form I

In this article, the solution-mediated polymorphic transformation of rifampicin was investigated and simulated in 3 solvents at 30°C. The solid-state form I and form II of rifampicin was characterized by powder X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR). To explore the relative stability, solubility data of form I and form II of rifampicin in butan-1-ol were determined using a dynamical method. In addition, Raman spectroscopy and focused beam reflectance measurement were used to in situ monitor the transformation of rifampicin from form II to form I. The liquid state concentration of rifampicin was measured by UV spectroscopic method. To investigate the effect of solvent on transformation, the transformation experiments were carried out in 3 solvents. Furthermore, a mathematical model was built to describe the kinetics of dissolution, nucleation, and growth processes during transformation by using experimental data. By combination of experimental and simulation results, it was found that the transformation process of rifampicin is controlled by dissolution of form II in heptane, whereas the transformation in hexane and octane was firstly controlled by dissolution of solid-state form and then controlled by growth of form I.

Supercritical antisolvent co-precipitation of rifampicin and ethyl cellulose

Rifampicin-loaded submicron-sized particles were prepared through supercritical anti-solvent process using ethyl cellulose as polymeric encapsulating excipient. Ethyl acetate and a mixture of ethyl acetate/dimethyl sulfoxide (70/30 and 85/15) were used as solvents for both drug and polymeric excipient. When ethyl acetate was used, rifampicin was crystallized separately without being embedded within the ethyl cellulose matrix while by using the ethyl acetate/dimethyl sulfoxide mixture, reduced crystallinity of the active ingredient was observed and a simultaneous precipitation of ethyl cellulose and drug was achieved. The effect of solvent/CO₂ molar ratio and polymer/drug mass ratio on the co-precipitates morphology and drug loading was investigated. Using the solvent mixture, co-precipitates with particle sizes ranging between 190 and 230nm were obtained with drug loading and drug precipitation yield from respectively 8.5 to 38.5 and 42.4 to 77.2% when decreasing the ethyl cellulose/rifampicin ratio. Results show that the solvent nature and the initial drug concentrations affect morphology and drug precipitation yield of the formulations. In vitro dissolution studies revealed that the release profile of rifampicin was sustained when co-precipitation was carried out with the solvent mixture. It was demonstrated that the drug to polymer ratio influenced amorphous content of the SAS co-precipitates. Differential scanning calorimetry thermograms and infrared spectra revealed that there is neither interaction between rifampicin and the polymer nor degradation of rifampicin during co-precipitation. In addition, stability stress tests on SAS co-precipitates were carried out at 75% relative humidity and room temperature in order to evaluate their physical stability. SAS co-precipitates were X-ray amorphous and remained stable after 6months of storage. The SAS co-precipitation process using a mixture of ethyl acetate/dimethyl sulfoxide demonstrates that this strategy can be successful for controlling rifampicin delivery.

The preparation, characterization, structure and dissolution analysis of apremilast solvatomorphs

Apremilast (AP) {systematic name: (S)-2-[1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl)ethyl]-4-acetamidoisoindoline-1,3-dione} is an inhibitor of phosphodieasterase-4 (PDE4) and is indicated for the treatment of adult patients with active psoriatic arthritis. The ability of AP to form solvates has been investigated and three solvatomorphs of AP, namely, the AP ethyl acetate hemisolvate, C22H24N2O7S·0.5C4H8O2, the AP toluene hemisolvate, C22H24N2O7S·0.5C7H8, and the AP dichloromethane monosolvate, C22H24N2O7S·CH2Cl2, were obtained. The three AP solvatomorphs were characterized by X-ray powder diffraction, thermogravimetric analysis and differential scanning calorimetry. Single-crystal X-ray diffraction was used to analyze the structures, crystal symmetry, packing modes, stoichiometry and hydrogen-bonding interactions of the solvatomorphs. In addition, dissolution analyses were performed to study the dissolution rates of different AP solvatomorph tablets in vitro and to make comparisons with commercial apremilast tablets (produced by Celgene); all three solvatomorphs showed similar dissolution rates and similar values of the similarity factor f2 in a comparison of their dissolution profiles.

Drug eluting antimicrobial vascular catheters: Progress and promise

Vascular catheters are critical tools in modern healthcare yet present substantial risks of serious bloodstream infections that exact significant health and economic burdens. Drug-eluting antimicrobial vascular catheters have become important tools in preventing catheter-related bloodstream infections and their importance is expected to increase as significant initiatives are expanded to eliminate and make the occurrence of these infections unacceptable. Here we review clinically significant and emerging drug-eluting antimicrobial catheters within the categories of antibiotic, antiseptic, novel bioactive agents and energy-enhanced drug eluting antimicrobial catheters. Important representatives of each category are reviewed from the standpoints of mechanisms of action, physical-chemical properties, safety, in vitro and clinical effectiveness.

Bioavailability of two licensed paediatric rifampicin suspensions: implications for quality control programmes

SETTING

To assess the revised World Health Organization-recommended dose of 10-20 mg/kg rifampicin (RMP), we studied the steady state pharmacokinetics of RMP in South African children who received standard treatment for drug-susceptible tuberculosis (TB).

OBJECTIVE

To determine the formulation effect on the pharmacokinetics of RMP.

DESIGN

RMP plasma concentrations were characterised in 146 children (median age 1.4 years, range 0.2-10.2). The morning dose on the day of the pharmacokinetic evaluation was administered as one of two RMP single-drug oral suspensions.

RESULTS

While one formulation achieved 2 h concentrations in the range of those observed in adults (median 6.54 mg/l, interquartile range [IQR] 4.47-8.84), the other attained a median bioavailability of only 25% of this, with a median 2 h concentration of 1.59 mg/l (IQR 0.89-2.38).

CONCLUSION

RMP is a key drug for the treatment of TB. It is critical that the quality of RMP suspensions used to treat childhood TB is ensured.

Study on four polymorphs of bifendate based on X-ray crystallography

Bifendate, a synthetic anti-hepatitis drug, exhibits polycrystalline mode phenomena with 2 polymorphs reported (forms A and B). Single crystals of the known crystalline form B and 3 new crystallosolvates involving bifendate solvated with tetrahydrofuran (C), dioxane (D), and pyridine (E) in a stoichiometric ratio of 1:1 were obtained and characterized by X-ray crystallography, thermal analysis, and Fourier transform infrared (FT-IR) spectroscopy. The differences in molecular conformation, intermolecular interaction and crystal packing arrangement for the four polymorphs were determined and the basis for the polymorphisms was investigated. The rotation of single bonds resulted in different orientations for the biphenyl, methyl ester and methoxyl groups. All guest solvent molecules interacted with the host molecule via an interesting intercalative mode along the [1 0 0] direction in the channel formed by the host molecules through weak aromatic stacking interactions or non-classical hydrogen bonds, of which the volume and planarity played an important role in the intercalation of the host with the guest. The incorporation of solvent-augmented rotation of the C–C bond of the biphenyl group had a striking effect on the host molecular conformation and contributed to the formation of bifendate polymorphs. Moreover, the simulated powder X-ray diffraction (PXRD) patterns for each form were calculated on the basis of the single-crystal data and proved to be unique. The single-crystal structures of the four crystalline forms are reported in this paper.

Effects of Surface Composition on the Aerosolisation and Dissolution of Inhaled Antibiotic Combination Powders Consisting of Colistin and Rifampicin

Colistin is often the only effective antibiotic against the respiratory infections caused by multidrug-resistant Gram-negative bacteria. However, colistin-resistant multidrug-resistant isolates have been increasingly reported and combination therapy is preferred to combat resistance. In this study, five combination formulations containing colistin (COL) and rifampicin (RIF) were prepared by spray drying. The lowest minimum inhibitory concentration (MIC) value against Pseudomonas aeruginosa PAO1 was measured for the formulation of COL/RIF = 4:1 with relatively high emitted doses (over 80%) and satisfactory fine particle fractions (over 60%). Data from X-ray photoelectron spectroscopy (XPS) and nano-time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed the surfaces of particles were mainly covered by rifampicin even for the formulation with a mass ratio of COL/RIF = 4:1. Because colistin is hygroscopic and rifampicin is hydrophobic, moisture absorption of combination formulations was significantly lower than the pure colistin formulation in the dynamic vapour sorption results. To investigate the dissolution characteristics, four dissolution test methods (diffusion Franz cell, modified Franz cell, flow-through and beaker methods) were employed and compared. The modified Franz cell method was selected to test the dissolution behaviour of aerosolised powder formulations to eliminate the effect of membrane on dissolution. The results showed that surface enrichment of hydrophobic rifampicin neither affected aerosolisation nor retarded dissolution rate of colistin in the combination formulations. For the first time, advanced surface characterisation techniques of XPS and ToF-SIMS have shown their capability to understand the effect of surface composition on the aerosolisation and dissolution of combination powders.

Uniform and amorphous rifampicin microspheres obtained by freezing induced LLPS during lyophilization

By lyophilization of rifampicin (RIF) solution in TBA/water with various solvent compositions, uniform and amorphous rifampicin (RIF) microspheres were produced. Using 55% TBA solution, the obtained RIF microspheres have a mono-dispersive size distribution with diameters range from 1 to 3 μm. The RIF microspheres are found to be amorphous by X-ray diffraction, and are expected to dissolve much faster than the crystalline RIF upon inhalation. Mechanistic investigation revealed that the amorphous RIF microspheres were formed due to liquid-liquid phase separation (LLPS) occurred during the freezing of the TBA/water solution. We also observed that the RIF microspheres can be readily phagocytized by activated THP-1 cells within 15 min. The suitable size distribution, high solubility, and readiness for phagocytosis by macrophages, all suggest that the lyophilized amorphous RIF microspheres could be potentially used as an anti-tuberculosis inhalation therapy. In addition, similar process was used to lyophilize TBA/water solutions of several other drugs, including rifaximin, rifapentine, paclitaxel, and isoniazid. We found that for drugs with appropriate physiochemical properties, such as paclitaxel and rifaximin, mono-dispersive microspheres could be obtained as well, which demonstrated that freezing induced LLPS could be utilized as a novel particle engineering methodology to produce drug microspheres by lyophilization.

Understanding pharmaceutical polymorphic transformations I: influence of process variables and storage conditions

The active pharmaceutical ingredient (API) of a dosage form is affected by number of mechanical and environmental factors which have a tendency to alter its crystalline state. Polymorphic transitions have been observed to occur during various unit operations like granulation, milling and compression. Forces of pressure, shear and temperature have an ability to induce alterations in crystal habit. A conversion in polymorphic form during a unit operation is very likely to affect the handling of API in the subsequent unit operation. Transitions have also been observed during storage of formulations where the relative humidity and temperature play a major role. An increase in temperature during storage can dehydrate or desolvate the crystal and hence produce crystal defects, whilst, high humidity conditions produce higher molecular mobility leading to either crystallization of API or alteration of its crystalline form.

Structural characterization of form I of anhydrous rifampicin

Crystal structure determination of form I of anhydrous rifampicin by X-ray powder diffraction data. Crystal morphology prediction revealed a good agreement with the images of the crystals.

Characterisation and evaluation of pharmaceutical solvates of Atorvastatin calcium by thermoanalytical and spectroscopic studies

BACKGROUND

Atorvastatin calcium (ATC), an anti-lipid biopharmaceutical class II drug, is widely prescribed as a cholesterol-lowering agent and is presently the world's best-selling medicine. A large number of crystalline forms of ATC have been published in patents. A variety of solid forms may give rise to different physical properties. Therefore, the discovery of new forms of this unusual molecule, ATC, may still provide an opportunity for further improvement of advantageous properties.

RESULTS

In the present work, eight new solvates (Solvate I-VIII) have been discovered by recrystallization method. Thermal behaviour of ATC and its solvates studied by DSC and TGA indicate similar pattern suggesting similar mode of entrapment of solvent molecules. The type of solvent present in the crystal lattice of the solvates is identified by GC-MS analysis and the stoichiometric ratio of the solvents is confirmed by 1HNMR. The high positive value of binding energy determined from thermochemical parameters indicates deep inclusion of the solvent molecules into the host cavity. The XRPD patterns point towards the differences in their crystallanity, however, after desolvation solvate II, III, IV, V and VIII transform to isostructral amorphous desolvated solvates. The order of crystallinity was confirmed by solution calorimetric technique as the enthalpy of solution is an indirect measure of lattice energy. All the solvates behaved endothermically following the order solvate-VIII (1-butanol solvate) < solvate-I (isoproplyate) < solvate-V (methanol solvate) < solvate-III (ethonalate) < solvate-VI (acetone ethanol solvate) < solvate-IV (t-butanol solvate) < solvate-II (THF solvate) < solvate-VII (mixed hemi-ethanol hydrate). The positive value of the heat capacity of the solvate formation provides information about the state of solvent molecules in the host lattice. The solvents molecules incorporated in the crystal lattice induced local chemical environment changes in the drug molecules which are observed in 13CP/MAS NMR spectral changes.

CONCLUSIONS

Aqueous solubility of solvate-VIII was found to be maximum, however, solvate-I and VIII showed better reduction in total cholesterol and triglyceride levels as compared to atorvastatin against triton-induced dyslipidemia.

Preparation of sustained release rifampicin microparticles for inhalation

Objectives

The aim of this research was to develop a novel carrier-free dry powder formulation of rifampicin for inhalation with controlled-release properties.

Methods

Rifampicin dihydrate (RFDH) microcrystals were prepared by a polymorphic transformation of rifampicin. The prepared RFDH microcrystals were coated with poly (dl-lactide-co-glycolide) or poly (dl-lactide), using a spray-dryer equipped with two different types of three-fluid (3F) spray nozzles. The physicochemical and aerodynamic properties of the coated RFDH microcrystals were compared with those of conventional matrix microparticles.

Key findings

The coated RFDH powder, encapsulating 50% of rifampicin, was successfully prepared by simple in-situ coating methods using two different types of 3F nozzles and had mass median aerodynamic diameter values of 3.5–4.5 µm. The thin flaky morphology of RFDH powders, providing good aerosolization properties, was maintained after coating. The coated RFDH formulations showed relatively low initial rifampicin release, compared with the uncoated RFDH crystals, followed by slow rifampicin release (about 70%) over 8 h in phosphate-buffered saline media (pH 7.4). Significant chemical degradations were not observed from the crystalline-structured RFDH formulations, while the amorphous-structured matrix formulations showed chemical degradation in six months.

Conclusions

These polymer coated RFDH formulations may be a valuable alternative in the treatment of tuberculosis since the carrier-free formulation offers the benefit of delivering a maximum-potency formulation of the antibiotic directly to the site of infection, and long drug residence times may be achieved by the controlled release of the drug.

Physicochemical properties of amorphous roxithromycin prepared by quench cooling of the melt or desolvation of a chloroform solvate

Roxithromycin is a poorly soluble antibacterial drug. The aim of this study was to prepare and characterize an amorphous form of roxithromycin. The amorphous form was prepared by desolvation of its chloroform solvate, and by quench cooling a melt of the crystalline monohydrated solid. The X-ray powder diffraction pattern of the desolvated chloroform solvate was indistinguishable from that of the glass prepared by melting, which indicated that it was amorphous. The roxithromycin glass was determined to be a fragile glass, but due to its high Kauzmann temperature (approximately 8°C), it should remain fairly stable upon refrigeration or even at room temperature. It was also determined that this glass remains stable in the presence of moisture with no indication of crystallization.

Redetermination of rifampicin pentahydrate revealing a zwitterionic form of the antibiotic

Rifampicin belongs to the family of naphthalenic ansamycin antibiotics. The first crystal structure of rifampicin in the form of the pentahydrate was reported in 1975 [Gadret, Goursolle, Leger & Colleter (1975). Acta Cryst. B 31, 1454-1462] with the rifampicin molecule assumed to be neutral. Redetermination of this crystal structure now shows that one of the phenol -OH groups is deprotonated, with the proton transferred to a piperazine N atom, confirming earlier spectroscopic results that indicated a zwitterionic form for the molecule, namely (2S,12Z,14E,16S,17S,18R,19R,20R,21S,22R,23S,24E)-21-acetyloxy-6,9,17,19-tetrahydroxy-23-methoxy-2,4,12,16,18,20,22-heptamethyl-8-[(E)-N-(4-methylpiperazin-4-ium-1-yl)formimidoyl]-1,11-dioxo-1,2-dihydro-2,7-(epoxypentadeca[1,11,13]trienimino)naphtho[2,1-b]furan-5-olate pentahydrate, C(43)H(58)N(4)O(12)·5H(2)O. The molecular structure of this antibiotic is stabilized by a system of four intramolecular O-H···O and N-H···N hydrogen bonds. Four of the symmetry-independent water molecules are arranged via hydrogen bonds into helical chains extending along [100], whereas the fifth water molecule forms only one hydrogen bond, to the amide group O atom. The rifampicin molecules interact via O-H···O hydrogen bonds, generating chains along [001]. Rifampicin pentahydrate is isostructural with recently reported rifampicin trihydrate methanol disolvate.