Drug–polymer intermolecular interactions in hot-melt extruded solid dispersions

Molecular modeling as a predictive tool for the development of solid dispersions

In this study molecular modeling is introduced as a novel approach for the development of pharmaceutical solid dispersions. A computational model based on quantum mechanical (QM) calculations was used to predict the miscibility of various drugs in various polymers by predicting the binding strength between the drug and dimeric form of the polymer. The drug/polymer miscibility was also estimated by using traditional approaches such as Van Krevelen/Hoftyzer and Bagley solubility parameters or Flory-Huggins interaction parameter in comparison to the molecular modeling approach. The molecular modeling studies predicted successfully the drug-polymer binding energies and the preferable site of interaction between the functional groups. The drug-polymer miscibility and the physical state of bulk materials, physical mixtures, and solid dispersions were determined by thermal analysis (DSC/MTDSC) and X-ray diffraction. The produced solid dispersions were analyzed by X-ray photoelectron spectroscopy (XPS), which confirmed not only the exact type of the intermolecular interactions between the drug-polymer functional groups but also the binding strength by estimating the N coefficient values. The findings demonstrate that QM-based molecular modeling is a powerful tool to predict the strength and type of intermolecular interactions in a range of drug/polymeric systems for the development of solid dispersions.

An investigation of nifedipine miscibility in solid dispersions using Raman spectroscopy

PURPOSE

Raman spectroscopy is potentially an extremely useful tool for the understanding of drug-polymer interactions in solid dispersions. This is examined and demonstrated for the case of solid dispersions of nifedipine in a polymeric substrate.

METHODS

Solid dispersions consisting of nifedipine and polyvinyl caprolactam--polyvinyl acetate--polyethylene glycol graft copolymer (Soluplus®) were prepared by freeze drying, melting and solvent evaporation at drug loadings of 10, 30, 50, 70 and 90% w/w. Drug-polymer interactions in the amorphous solid dispersion were estimated by Raman spectroscopy. The correlation between the solid state stability of the drug in a solid dispersion and the extent of drug-polymer interaction was monitored by X-ray diffractometry.

RESULTS

The miscibility limit of nifedipine-Soluplus® was found to be 30% w/w drug loading for all preparation methods. The drug was found to interact with Soluplus®, through a hydrophilic interaction identified by infrared spectroscopy and a hydrophobic interaction which could be quantified by Raman spectroscopy. The average extent of the drug-polymer interaction in the studied amorphous samples at equivalent drug loading was similar, regardless of the preparation method. Inhomogeneities in samples prepared by melting contributed to a wider variation in drug-polymer interaction and poorer solid state stability, in terms of its crystallization tendency.

CONCLUSIONS

Raman spectroscopy was shown to be a useful technique in classifying miscibility levels based on the hydrophobic interaction between the drug and the polymer. Different drug loadings showed varying degrees of drug-polymer interaction, and hence variable solid state stability of the solid dispersion.

Studies of intermolecular interactions in solid dispersions using advanced surface chemical analysis

The aim of this study is to utilise an advanced surface chemical analysis based on X-ray photoelectron spectroscopy (XPS) to determine and characterise drug/polymer interactions in solid dispersions manufactured via hot melt extrusion (HME).

Two-dimensional asynchronous spectrum with auxiliary cross peaks in probing intermolecular interactions

A new approach called “asynchronous spectrum with auxiliary peaks (ASAP)” is proposed for generating a 2D asynchronous spectrum to investigate the intermolecular interaction between two solutes (P and Q) dissolved in the same solution.

An in-vitro–in-vivo taste assessment of bitter drug: comparative electronic tongues study

Objectives

The efficiency of the Astree e-tongue and Taste Sensing system TS5000Z for the evaluation of the taste masking effect of hot melt extruded formulations was investigated in this study.

Methods

Hot melt extrusion (HME) processing was optimized using Randcastle single screw extruder (USA) to manufacture extrudates with desirable characteristics. Cationic model drug propranolol HCl (PRP) was processed with the anionic polymers – Eudragit L100 (L100) and Eudragit L100-55 (Acryl-EZE). Solid state of the drug in polymer matrices was evaluated by scanning electron microscopy (SEM), differential scanning calorimetry, particle size analysis, Fourier transform infrared (FTIR) and Nuclear magnetic resonance (NMR) analysis. In-vitro taste masking efficiency of the two polymers was performed by using two different e-tongues (Astree e-tongue and TS5000Z). The results obtained from both e-tongues were further compared and contrast to find out the sensor outputs in all formulations.

Key findings

Solid state analysis of the extruded formulations revealed the presence of amorphous PRP. Both e-tongues were able to detect the taste masking variations of the extrudates and were in good agreement with the in-vivo results obtained from a panel of six healthy human volunteers (R2 > 0.84). However, each e-tongue sensor demonstrated different sensitivity, suggesting a careful consideration of the experimental findings during melt extrusion, is necessary for the development of taste-masked formulations. Furthermore, FTIR spectroscopy and NMR studies revealed possible drug polymer intermolecular interactions as the mechanism of successful taste masking.

Conclusions

HME can effectively be used to manufacture taste-masked extruded formulations, while both e-tongues demonstrated satisfactory taste analysis for the development of taste-masked formulations.

Hot melt extruded amorphous solid dispersion of posaconazole with improved bioavailability: investigating drug-polymer miscibility with advanced characterisation

Invasive antifungal infections are reasons for morbidity and mortality in immunogenic patients worldwide. Posaconazole is a most promising antifungal agent against all types of invasive infections with high % of cure rate. The marketed suspension formulation has low bioavailability and is needed to be taken with food. In this paper, PCZ hot melt extruded amorphous solid dispersion (SD) with immediate release and improved bioavailability was prepared using Soluplus (Sol) as primary carrier for solubilization. Surfactants such as PEG 400, Lutrol F27, Lutrol F68, and TPGS are also used in combination with Soluplus to improve the physicochemical performance of the formulation when it comes in contact with GI (gastrointestinal) fluid. Drug-polymer miscibility of SD was investigated using advanced techniques. In the in vivo study, the AUC_(0–72) and C_max of PCZ/Soluplus were 11.5 and 11.74 time higher than those of pure PCZ. The formulation of the extrudate SD had an AUC_(0–72) and C_max higher than those with the commercial capsule (Noxafil). Molecular dynamic (MD) simulation studies were carried out using in silico molecular modelling to understand the drug-polymer intermolecular behaviour. The results of this research ensure enhanced dissolution and bioavailability of the solid dispersion of PCZ prepared by HME compared with the PCZ suspension.

Interactions between drugs and polymers influencing hot melt extrusion

Objectives

Hot melt extrusion (HME) as a technique for producing amorphous solid dispersion (ASD) has been widely used in pharmaceutical research. The biggest challenge for the application of HME is the thermal degradation of drug, poor physical stability of ASD and precipitation of drug during dissolution. Interactions between drugs and polymers may play an important role in overcoming these barriers. In this review, influence of drug–polymer interactions on HME and the methods for characterizing the drug–polymer interactions were reviewed.

Key findings

Strong drug–polymer interactions, especially ionic interactions and hydrogen bonds, are helpful to improving the thermal stability of drug during HME, enhancing the physical stability of ASD during storage and maintaining supersaturated solution after dissolution in gastrointestinal tract. The interactions can be quantitatively and qualitatively characterized by many analysing methods.

Conclusions

As many factors collectively determine the properties of HME products, drug–polymer interactions play an extremely important role. However, the action mechanisms of drug–polymer interactions need intensive investigation to provide more useful information for optimizing the formulation and the process parameters of HME.

An in-vivo and in-vitro taste masking evaluation of bitter melt-extruded drugs

Objectives

The purpose of this study was to investigate the potential of hot-melt extrusion (HME) for masking the taste of bitter active pharmaceutical ingredients (APIs) when incorporated into different polymer formulations.

Methods

Extrudates were produced by HME using two water soluble cationic model drugs (cetirizine HCl and verapamil HCl) processed with various grades of anionic polymers (Eudragit L100 and Eudragit L100-55 (Acryl EZE)). The process was optimised by using a single screw extruder to produce extruadates with the desirable characteristics.

Key findings

In-vivo results obtained from a panel of six healthy human volunteers demonstrated that the HME extruded formulations improved the taste significantly compared with that of the pure APIs. In addition, an in-vitro evaluation carried out by an Astree e-tongue equipped with seven specific sensors demonstrated significant taste improvement of the extrudates compared with placebo polymers and the pure APIs. Furthermore, the extrudates characterised by SEM, X-ray and differential scanning calorimetry studies showed the existence of molecularly dispersed APIs while in-vitro dissolution showed fast release for all drug substances.

Conclusions

HME can effectively be used to mask the taste of bitter APIs by enhancing drug–polymer interactions.

Development of solid dispersions of artemisinin for transdermal delivery

Solid dispersions of the poorly soluble drug artemisinin were developed using polymer blends of polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) with the aim of enhancing solubility and in vitro permeation of artemisinin through skin. Formulations were characterised using a combination of molecular dynamics (MD) simulations, differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). Solubility of artemisinin was determined in two solvents: de-ionised water and phosphate buffered saline (PBS; pH 7.4), while in vitro drug permeation studies were carried out using rabbit skin as a model membrane. MD simulations revealed miscibility between the drug and polymers. DSC confirmed the molecular dispersion of the drug in the polymer blend. Decrease in crystallinity of artemisinin with respect to polymer content and the absence of specific drug-polymer interactions were confirmed using XRD and FT-IR, respectively. The solubility of artemisinin was dramatically enhanced for the solid dispersions, as was the permeation of artemisinin from saturated solid-dispersion vehicles relative to that from saturated solutions of the pure drug. The study suggests that high energy solid forms of artemisinin could possibly enable transdermal delivery of artemisinin.