Thermal stability of amorphous nimesulide: from glass formation to crystal growth and thermal degradation.

Thermally induced physico-chemical transformations in amorphous nimesulide were studied by means of differential scanning calorimetry (DSC), thermogravimetry, and Raman microscopy. The equilibrium glass transition temperature was found to be Tg0 = 10-15 °C, and the relaxation motions were found to be temperature-dependent. Crystal growth from the amorphous phase was found to be crucially dependent on the presence of mechanical defects that serve as centers for heterogeneous nucleation. The large amounts of mechanical defects significantly decrease the activation energy of the macroscopic crystallization; the positions of the crystallization peaks and their asymmetry/shape remain however almost unchanged. At laboratory temperature, powdered nimesulide fully crystallizes within several hours, with an absolute majority of the crystalline phase being formed as the thermodynamically stable form I polymorph. Amorphous nimesulide does not crystallize from the free smooth surface (no trace of formed crystallites was found by optical microscopy after 30 days at laboratory temperature). Nimesulide was found to be very stable at temperatures above its melting point of 147.5 °C; thermal degradation starts to proceed slowly at 200 °C. Mutual correlations between the macroscopic and microscopic crystal growth processes and between the viscous flow and structural relaxation motions were discussed based on the values of the corresponding activation energies. A link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model, and microscopic crystal growth was proposed.

Thermal degradation of Affinisol HPMC: Optimum Processing Temperatures for Hot Melt Extrusion and 3D Printing.

PURPOSE: Affinisol HPMC HME is a new popular form of hypromellose specifically designed for the hot melt extrusion and 3D printing of pharmaceutical products. However, reports of its thermal stability include only data obtained under inert N2 atmosphere, which is not consistent with the common pharmaceutical practice. Therefore, detailed investigation of its real-life thermal stability in air is paramount for identification of potential risks and limitations during its high-temperature processing. METHODS: In this work, the Affinisol HPMC HME 15LV powder as well as extruded filaments will be investigated by means of thermogravimetry, differential scanning calorimetry and infrared spectroscopy with respect to its thermal stability. RESULTS: The decomposition in N2 was proceeded in accordance with the literature data and manufacturer's specifications: onset at ~260°C at 0.5°C·min-1, single-step mass loss of 90-95%. However, in laboratory or industrial practice, high-temperature processing is performed in the air, where oxidation-induced degradation drastically changes. The thermogravimetric mass loss in air proceeded in three stages: ~ 5% mass loss with onset at 150°C, ~ 70% mass loss at 200°C, and ~ 15% mass loss at 380°C. Diffusion of O2 into the Affinisol material was identified as the rate-determining step. CONCLUSION: For extrusion temperatures ≥170°C, Affinisol exhibits a significant degree of degradation within the 5 min extruder retention time. Hot melt extrusion of pure Affinisol can be comfortably performed below this temperature. Utilization of plasticizers may be necessary for safe 3D printing.

Indomethacin: Effect of Diffusionless Crystal Growth on Thermal Stability during Long-Term Storage.

Differential scanning calorimetry and Raman spectroscopy were used to study the nonisothermal and isothermal crystallization behavior of amorphous indomethacin powders (with particle sizes ranging from 50 to 1000 µm) and their dependence on long-term storage conditions, either 0-100 days stored freely at laboratory ambient temperatures and humidity or placed in a desiccator at 10 °C. Whereas the γ-form polymorph always dominated, the accelerated formation of the α-form was observed in situations of heightened mobility (higher temperature and heating rate), increased amounts of mechanically induced defects, and prolonged free-surface nucleation. A complex crystallization behavior with two separated crystal growth modes (originating from either the mechanical defects or the free surface) was identified both isothermally and nonisothermally. The diffusionless glass-crystal (GC) crystal growth was found to proceed during the long-term storage at 10 °C and zero humidity, at the rate of ~100 µm of the γ-form surface crystalline layer being formed in 100 days. Storage at the laboratory temperature (still below the glass transition temperature) and humidity led only to a negligible/nondetectable GC growth for the fine indomethacin powders (particle size below ~150 µm), indicating a marked suppression of GC growth by the high density of mechanical defects under these conditions. The freely stored bulk material with no mechanical damage and a smooth surface exhibited zero traces of GC growth (as confirmed by microscopy) after >150 days of storage. The accuracy of the kinetic predictions of the indomethacin crystallization behavior was rather poor due to the combined influences of the mechanical defects, competing nucleation, and crystal growth processes of the two polymorphic phases as well as the GC growth complex dependence on the storage conditions within the vicinity of the glass transition temperature. Performing paired isothermal and nonisothermal kinetic measurements is thus highly recommended in macroscopic crystallization studies of drugs with similarly complicated crystal growth behaviors.

Indomethacin: The Interplay between Structural Relaxation, Viscous Flow and Crystal Growth.

Non-isothermal differential scanning calorimetry (DSC) was used to study the influences of particle size (daver) and heating rate (q+) on the structural relaxation, crystal growth and decomposition kinetics of amorphous indomethacin. The structural relaxation and decomposition processes exhibited daver-independent kinetics, with the q+ dependences based on the apparent activation energies of 342 and 106 kJ·mol-1, respectively. The DSC-measured crystal growth kinetics played a dominant role in the nucleation throughout the total macroscopic amorphous-to-crystalline transformation: the change from the zero-order to the autocatalytic mechanism with increasing q+, the significant alteration of kinetics, with the storage below the glass transition temperature, and the accelerated crystallization due to mechanically induced defects. Whereas slow q+ led to the formation of the thermodynamically stable γ polymorph, fast q+ produced a significant amount of the metastable α polymorph. Mutual correlations between the macroscopic and microscopic crystal growth processes, and between the viscous flow and structural relaxation motions, were discussed based on the values of the corresponding activation energies. Notably, this approach helped us to distinguish between particular crystal growth modes in the case of the powdered indomethacin materials. Ediger's decoupling parameter was used to quantify the relationship between the viscosity and crystal growth. The link between the cooperativity of structural domains, parameters of the Tool-Narayanaswamy-Moynihan relaxation model and microscopic crystal growth was proposed.

Matrix Tablets Based on Chitosan-Carrageenan Polyelectrolyte Complex: Unique Matrices for Drug Targeting in the Intestine.

The present study focused on the more detailed characterization of chitosan-carrageenan-based matrix tablets with respect to their potential utilization for drug targeting in the intestine. The study systematically dealt with the particular stages of the dissolution process, as well as with different views of the physico-chemical processes involved in these stages. The initial swelling of the tablets in the acidic medium based on the combined microscopy-calorimetry point of view, the pH-induced differences in the erosion and swelling of the tested tablets, and the morphological characterization of the tablets are discussed. The dissolution kinetics correlated with the rheological properties and mucoadhesive behavior of the tablets are also reported, and, correspondingly, the formulations with suitable properties were identified. It was confirmed that the formation of the chitosan-carrageenan polyelectrolyte complex may be an elegant and beneficial alternative solution for the drug targeting to the intestine by the matrix tablet.

3D-Printed Coating of Extended-Release Matrix Tablets: Effective Tool for Prevention of Alcohol-Induced Dose Dumping Effect.

Tablets used for extended drug release commonly contain large amounts of drugs. The corresponding drug release mechanism thus has to be well-known and invariable under numerous conditions in order to prevent any uncontrolled drug release. Particularly important is the stability and invariability of the release mechanism in the presence of alcohol due to the possible occurrence of the dose dumping effect. The effect of 3D printing (3DP) coating on the drug release mechanism and the drug release rate was studied as a possible tool for the prevention of the alcohol-induced dose dumping effect. Three types of matrix tablets (hydrophilic, lipophilic, and hydrophilic-lipophilic) were prepared by the direct compression method and coated using 3DP. The commercial filament of polyvinyl alcohol (PVA) and the filament prepared from hypromellose by hot melt extrusion (HME) were used as coating materials. Both coating materials were characterized by SEM, DSC, Raman spectroscopy, and PXRD during particular stages of the processing/coating procedure. The dissolution behavior of the uncoated and coated tablets was studied in the strongly acidic (pH 1.2) and alcoholic (40% of ethanol) dissolution media. The dissolution tests in the alcoholic medium showed that the Affinisol coating was effective in preventing the dose dumping incidence. The dissolution tests in the acidic dissolution media showed that the Affinisol coating can also be useful for the delayed release of active substances.

A Critical Overview of FDA and EMA Statistical Methods to Compare In Vitro Drug Dissolution Profiles of Pharmaceutical Products.

A drug dissolution profile is one of the most critical dosage form characteristics with immediate and controlled drug release. Comparing the dissolution profiles of different pharmaceutical products plays a key role before starting the bioequivalence or stability studies. General recommendations for dissolution profile comparison are mentioned by the EMA and FDA guidelines. However, neither the EMA nor the FDA provides unambiguous instructions for comparing the dissolution curves, except for calculating the similarity factor f2. In agreement with the EMA and FDA strategy for comparing the dissolution profiles, this manuscript provides an overview of suitable statistical methods (CI derivation for f2 based on bootstrap, CI derivation for the difference between reference and test samples, Mahalanobis distance, model-dependent approach and maximum deviation method), their procedures and limitations. However, usage of statistical approaches for the above-described methods can be met with difficulties, especially when combined with the requirement of practice for robust and straightforward techniques for data evaluation. Therefore, the bootstrap to derive the CI for f2 or CI derivation for the difference between reference and test samples was selected as the method of choice.

Influence of particle size and manufacturing conditions on the recrystallization of amorphous Enzalutamide.

Non-isothermal differential scanning calorimetry was used to study the influences of particle size and mechanically induced defects on the recrystallization kinetics of amorphous Enzalutamide. Enzalutamide prepared by hot melt extrusion and spray-drying was used as a model material. The recrystallization rate was primarily accelerated by the presence of the processing-damaged surface of the powder particles. The actual surface/volume ratio associated with decreasing particle size fulfilled only a secondary role. Interestingly, higher quench rate during the extrusion led to a formation of thermally less stable material (with the worse stability being manifested via lower activation energy of crystal growth in the amorphous matrix). This can be the consequence of the formation of looser structure more prone to rearrangements. The recrystallization kinetics of the prepared Enzalutamide amorphous materials was described by the two-parameter autocatalytic kinetic model. The modified single-curve multivariate kinetic analysis (optimized for the data obtained at heating rate 0.5 °C•min-1) was used to calculate the extrapolated kinetic predictions of long-term isothermal crystal growth. The predictions were made for the temperatures from the range of drug shelf-life and processing for each particle size fraction. By the combination of the mass-weighted predictions for the individual powder fractions it was possible to obtain a very reasonable (temperature-extrapolated) prediction of the crystallization rate for the as-prepared unsieved powdered amorphous Enzalutamide.

The effect of alcohol on ionizing and non-ionizing drug release from hydrophilic, lipophilic and dual matrix tablets.

The aim of this work was to investigate and quantitatively evaluate the effect of presence of alcohol on in vitro release of ionizing and non-ionizing drug from hydrophilic, lipophilic and hydrophilic-lipophilic matrix tablets. The Food and Drug Administration (FDA) recommends in vitro dissolution testing of extended release formulations in ethanolic media up to 40% because of possible alcohol-induced dose dumping effect. This study is focused on comparison of the dissolution behavior of matrix tablets (based on hypromellose and/or glyceryl behenate as retarding agent) of the same composition containing different type of drug - ionizing tramadol hydrochloride (TH) and non-ionizing pentoxifylline (PTX). The dissolution tests were performed in acidic medium (pH 1.2) and in alcoholic medim (20%, 40% of ethanol) and the changes of tablets were observed also photographically. It was found that the alcohol resistence of the hydrophilic-lipophilic formulations with TH and the hydrophilic-lipophilic formulations with PTX containing a higher amount of hypromellose does not reflect the alcohol resistence of the formulations with pure hypromellose or glyceryl behenate. Both hydrophilic-lipophilic formulation with TH and more lipophilic formulation with PTX show significant alcohol dose dumping effect.

Comparative evaluation of the use of dry binders in a physical mixture or as a coprocessed dry binder in matrix tablets with extended drug release.

This paper evaluates and compares the properties of directly compressible tabletting materials and matrix tablets containing a combination of α-lactose monohydrate and microcrystalline cellulose in the 3:1 ratio in a physical mixture and in a coprocessed dry binder. Tested parameters include flow properties, compressibility, compactibility and the rate of drug release from tablets. Compressibility is evaluated by means of the energy profile of the compression process. Compactibility is evaluated by means of the tensile strength of the tablets. Dissolution testing is done using the rotating basket method. Dissolution profiles are evaluated by non-linear regression analysis. Total energy of compression and plasticity values were higher in tabletting materials with the coprocessed dry binder. Increasing additions of polyvinyl alcohol decreased the values of total energy of compression, plasticity, tensile strength of tablets and drug release rate. Dissolution behaviour of tablets, which contained the physical mixture or coprocessed dry binder and the same amount of polyvinyl alcohol, was comparable.

Formulation and dissolution kinetics study of hydrophilic matrix tablets with tramadol hydrochloride and different co-processed dry binders.

The aim of this study is to present the possibility of using of co-processed dry binders for formulation of matrix tablets with drug controlled release. Hydrophilic matrix tablets with tramadol hydrochloride, hypromellose and different co-processed dry binders were prepared by direct compression method. Hypromelloses Methocel™ K4M Premium CR or Methocel™ K100M Premium CR were used as controlled release agents and Prosolv® SMCC 90 or Disintequik™ MCC 25 were used as co-processed dry binders. Homogeneity of the tablets was evaluated using scanning electron microscopy and energy dispersive X-ray microanalysis. The release of tramadol hydrochloride from prepared formulations was studied by dissolution test method. The dissolution profiles obtained were evaluated by non-linear regression analysis, release rate constants and other kinetic parameters were determined. It was found that matrix tablets based on Prosolv® SMCC 90 and Methocel™ Premium CR cannot control the tramadol release effectively for >12h and tablets containing Disintequik™ MCC 25 and Methocel™ Premium CR >8h.

STUDY OF DUAL MATRIX TABLETS CONTAINING HYPROMELLOSE OF DIFFERENT VISCOSITY DEGREE AND GLYCERYL DIBEHENATE.

Studies are described on the compressibility of directly compressible tableting materials containing two viscosity types of hypromellose in two concentrations and tableting materials containing additional glyceryl dibehenate, also in two concentrations. Compressibility is evaluated by means of the energy profile of the compression process and determination of tensile strength of tablets. Dissolution test examines the rate of release of the active ingredient from matrix tablets, which is subsequently evaluated mathematically. Increased concentrations of both hypromelloses and an addition of glyceryl dibehenate into tablets with both types of hypromellose improved compressibility. The rate of drug release was decreased with increasing viscosity degree of hypromellose and its increasing concentration. An addition of glyceryl dibehenate exerted the same influence on release as increased concentrations of the pertinent hypromellose.

Compressibility of tableting materials and properties of tablets with glyceryl behenate.

The paper studies the compressibility of directly compressible tableting materials with dry binders, spray-dried lactose and microcrystalline cellulose, and glyceryl dibehenate at various concentrations. Compressibility was evaluated by means of the energy profile of compression and tensile strength of tablets. Release rate of the active ingredient, salicylic acid, from the tablets was also examined. In the case of microcrystalline cellulose, a higher concentration of glyceryl dibehenate increased the strength of tablets, while this did not occur in the case of spray-dried lactose. Increasing concentration of glyceryl dibehenate prolonged the release of salicylic acid; however, no statistically significant difference was found compared to the type of the dry binder used.

Inhibition of cholinesterase by dialkylcarbamates.

The pI50 index and separation coefficients of chosen 3-N,N-diethylaminophenyl-N',N'-dialkylcarbamates were determined. Index pL50 (pI50 = negative logarithm of molar concentration of inhibitor inhibiting the enzyme activity by 50%) describes the effectiveness of the inhibitor. The rate of ability of the inhibitor to pass the blood-brain barrier is usually described by the separation coefficient in a system n-octanol/water (K(ow)). Obtained results were compared with pL50 and K(ow) of Exelon, the commercially used drug against the Alzheimer's disease.

In vitro inhibition of cholinesterases by carbamates--a kinetic study.

Kinetics and mechanism of in vitro hydrolyses of acetylcholine and acetylthiocholine by carbamates were studied in a batch reactor at 25 degrees C, pH 8, and ionic strength of 0.11 M. Every hydrolysis was monitored by 3-4 independent methods. All studied hydrolyses can be described by the model of competitive inhibition with an irreversible step (k3). A table of obtained average values of rate constants and discussion of the resultes are given.

New findings about Ellman's method to determine cholinesterase activity.

The original Ellman's spectrophotometrical method for cholinesterase activity determination uses 5,5'-dithiobis-2-nitrobenzoic acid (DTNB, Ellman's reagent) as a chromogen and records the level of cholinesterase activity as an increase of absorbance at 412 nm. Although this procedure usually poses no problem, exceptions arise when the concentration of DTNB is far higher than the concentration of acetylthiocholine (ATCH). It was found that the ratio of concentrations of DTNB/ATCH is an important parameter for the ATCH hydrolysis course: high excess of DTNB decreases the hydrolysis rate resulting in a lower measured enzyme activity. Our experiments indicate that this influence of DTNB concentration can be explained by the inhibition of ATCH hydrolysis by DTNB.

Kinetics of 13 new cholinesterase inhibitors.

Kinetics of hydrolysis of acetylcholine and acetylthiocholine by two types of acetylcholinesterase and butyrylcholinesterase inhibited by 13 new inhibitors (5 carbamates and 8 carbazates--hydrazinium derivatives) was measured in vitro in a batch reactor at 25 degrees C, pH 8, ionic strength 0.11 M and enzyme activity 3.5 U by four nondependent analytical methods. Sevin, rivastigmin (Exelon) and galantamin (Reminyl) served as comparative inhibiting standards. Kinetics of hydrolyses inhibited by all studied carbamates, sevin, carbazates (with exceptions) and rivastigmin (with exceptions) can be simulated by the competitive inhibition model with irreversible reaction between enzyme and inhibitor. Galantamin does not fulfil this model. In positive simulations, the value of inhibition (carbamoylation) rate constant k3 was calculated, describing the reaction velocity between the given enzyme and inhibitor. Physiologically important hydrolyses of acetylcholine catalyzed by acetylcholinesterase from electric eel or bovine erythrocytes and butyrylcholinesterase from horse plasma can be most quickly inhibited by carbamoylation of the mentioned enzymes by the 3-N,N-diethylaminophenyl-N'-(1-alkyl) carbamates 4 and 5. Probably this is due to a long enough hydrocarbon aliphatic substituent (hexyl and octyl) on the amidic nitrogen atom. The tested carbazates failed as inhibitors of cholinesterases. The regeneration ability of the inhibited enzymes was not measured.

Kinetics of total enzymatic hydrolysis of acetylcholine and acetylthiocholine.

Kinetics and the mechanism of total in vitro hydrolyses (i.e. up to the exhaustion of substrate) of acetylcholine and acetylthiocholine by acetylcholinesterase and butyrylcholinesterase were studied in vitro in a batch reactor at 25 degrees C, pH 8 and ionic strength of 0.11 M. Every hydrolysis was monitored by 2-3 independent analytical methods. All studied types of enzymatic hydrolyses fulfilled the Michaelis-Menten reaction scheme with the irreversible second step. A table of obtained average values of rate constants and estimations of initial molar enzyme concentrations, and discussion of the results are presented.

Two new methods monitoring kinetics of hydrolysis of acetylcholine and acetylthiocholine.

Hydroxylamine and HPLC methods, measuring in vitro kinetics of enzymatic hydrolysis of acetylcholine or acetylthiocholine by cholinesterases, are described. The hydroxylamine method determines the dependence of substrate concentration vs. time, the HPLC method is able to measure simultaneously the time dependences of substrate and both primary products, choline or thiocholine, and acetic acid. Practical determinations are shown, comparison with known (above all Ellman's and pH-stat) methods, advantages and disadvantages are discussed.