A calorimetric investigation into the interaction between paracetamol and polyethlene glycol 4000 in physical mixes and solid dispersions

Obtaining two polymorphic forms of paracetamol within the phase diagram with PEG 1500

Studies of the interactions between paracetamol, chosen as model active ingredient, and PEG 1500, a pharmaceutical carrier, are conducted in the solid state. Solid dispersions of PEG 1500 and paracetamol were prepared in different mass ratios. Two temperature cycles are then applied and the characterization is carried out by DSC and X-ray powder diffraction. Following this, a phase diagram is established for each cycle. On second heating, the metastable Form II of paracetamol is obtained within the PEG-based matrix. However, on the second heating, for paracetamol contents higher than 65%, Form I or form II is obtained randomly.

Solvent-Mediated Polymorphic Transformations in Molten Polymers: The Account of Acetaminophen

Solvent-mediated polymorphic transformations (SMPTs) employing nonconventional solvents (polymer melts) is an underexplored research topic that limits the application of polymer-based formulation processes. Acetaminophen (ACM), a widely studied active pharmaceutical ingredient (API), is known to present SMPTs spontaneously (<30 s) in conventional solvents such as ethanol. In situ Raman spectroscopy was employed to monitor the induction time for the SMPT of ACM II to I in polyethylene glycol (PEG) melts of different molecular weights (Mw, 4000, 10 000, 20 000, 35 000 g/mol). The results presented here demonstrate that the induction time for the SMPT of ACM II to I in PEG melts is driven by its diffusivity through the polymer melts. Compared to conventional solvents (i.e., ethanol) the mass transfer (diffusion coefficient, D) in melts is significantly hindered (Dethanol = 4.84 × 10-9 m2/s > DPEGs = 5.32 × 10-11-8.36 × 10-14 m2/s). Ultimately, the study proves that the induction time for the SMPT can be tuned by understanding the dispersant's physicochemical properties (i.e., η) and, thus, the D of the solute in the dispersant. This allows one to kinetically access and stabilize metastable forms or delay their transformations under given process conditions.

Pharmaceutical amorphous solid dispersion: A review of manufacturing strategies

Amorphous solid dispersions (ASDs) are popular for enhancing the solubility and bioavailability of poorly water-soluble drugs. Various approaches have been employed to produce ASDs and novel techniques are emerging. This review provides an updated overview of manufacturing techniques for preparing ASDs. As physical stability is a critical quality attribute for ASD, the impact of formulation, equipment, and process variables, together with the downstream processing on physical stability of ASDs have been discussed. Selection strategies are proposed to identify suitable manufacturing methods, which may aid in the development of ASDs with satisfactory physical stability.

Compression-Induced Phase Transitions of Bicalutamide

The formation of solid dispersions with the amorphous drug dispersed in the polymeric matrix improves the dissolution characteristics of poorly soluble drugs. Although they provide an improved absorption after oral administration, the recrystallization, which can occur upon absorption of moisture or during solidification and other formulation stages, serves as a major challenge. This work aims at understanding the amorphization-recrystallization changes of bicalutamide. Amorphous solid dispersions with poly(vinylpyrrolidone-co-vinyl acetate) (PVP/VA) were obtained by either ball milling or spray drying. The applied processes led to drug amorphization as confirmed using X-ray diffraction and differential scanning calorimetry. Due to a high propensity towards mechanical activation, the changes of the crystal structure of physical blends of active pharmaceutical ingredient (API) and polymer upon pressure were also examined. The compression led to drug amorphization or transition from form I to form II polymorph, depending on the composition and applied force. The formation of hydrogen bonds confirmed using infrared spectroscopy and high miscibility of drug and polymer determined using non-isothermal dielectric measurements contributed to the high stability of amorphous solid dispersions. They exhibited improved wettability and dissolution enhanced by 2.5- to 11-fold in comparison with the crystalline drug. The drug remained amorphous upon compression when the content of PVP/VA in solid dispersions exceeded 20% or 33%, in the case of spray-dried and milled systems, respectively.

In-situ freeze-drying - forming amorphous solids directly within capsules: An investigation of dissolution enhancement for a poorly soluble drug

Conversion into the amorphous form enhances the dissolution of poorly soluble drugs, however the barrier to market for medicines containing an amorphous drug is poor stability. The aim was to produce the amorphous form of a drug within a capsule, without thermal or mechanical stress during manufacture. To facilitate this aim, the mechanism for drug-polymer interaction was explored. Nifedipine and polyvinylpyrrolidone were dissolved in tert-butanol at different drug/polymer ratios. These solutions were dispensed into gelatin capsules and freeze-dried. Differential scanning calorimetry (DSC) & novel FT-IR analysis based on peak symmetry measurements confirmed the absence of crystallinity when polyvinylpyrrolidone exceeded 50%w/w. Capsules containing 10 mg of nifedipine were amorphous and stable for over 3 months at ≈40 °C. Evidence of hydrogen bonding between the N-H group of nifedipine and the C=O group of PVP was observed and this interaction inhibited nifedipine crystallisation. PVP’s high affinity for water and the nifedipine-polymer interaction lead to a significant dissolution rate enhancement. The freeze-dried capsule, 10%w/w nifedipine/PVP, had the highest dissolution rate constant of 0.37 ± 0.05 min⁻¹, and the lowest time to achieve 50% dissolution or t_1/2 of 1.88 ± 0.05 min. This formulation reached 80% dissolved in less than 6 min whereas the equivalent marketed liquid filled nifedipine capsule took 3 times longer to reach 80% dissolution.

Amorphous solid dispersions: Rational selection of a manufacturing process

Amorphous products and particularly amorphous solid dispersions are currently one of the most exciting areas in the pharmaceutical field. This approach presents huge potential and advantageous features concerning the overall improvement of drug bioavailability. Currently, different manufacturing processes are being developed to produce amorphous solid dispersions with suitable robustness and reproducibility, ranging from solvent evaporation to melting processes. In the present paper, laboratorial and industrial scale processes were reviewed, and guidelines for a rationale selection of manufacturing processes were proposed. This would ensure an adequate development (laboratorial scale) and production according to the good manufacturing practices (GMP) (industrial scale) of amorphous solid dispersions, with further implications on the process validations and drug development pipeline.

Amiodarone hydrochloride: enhancement of solubility and dissolution rate by solid dispersion technique

abstract Amiodarone HCl is an antiarrhythmic agent, which has low aqueous solubility and presents absorption problems. This study aimed to develop inclusion complexes containing hydrophilic carriers PEG 1500, 4000 and 6000 by fusion and kneading methods in order to evaluate the increase in solubility and dissolution rate of amiodarone HCl. The solid dispersion and physical mixtures were characterized by X-ray diffraction, FT-IR spectra, water solubility and dissolution profiles. Both methods and carriers increased the solubility of drug, however PEG 6000 enhanced the drug solubility in solid dispersion better than other carriers. Different media were evaluated for the solubility study, including distilled water, acid buffer pH 1.2, acetate buffer pH 4.5 and phosphate buffer pH 6.8 at 37 ºC. Based on the evaluation of the results obtained in the study phase solubility carriers PEG 4000 and PEG 6000 were selected for the preparation of the physical mixture and solid dispersion. All formulations were prepared at drug-carrier ratios of 1:1 to 1:10(w/w). The results of in vitro release studies indicated that the solid dispersion technique by fusion method in proportion of 1:10 (w/w) increased significantly the dissolution rate of the drug. X-ray diffraction studies showed reduced drug crystallinity in the solid dispersions. FT-IR demonstrated interactions between the drug and polymers.

Dissolution Enhancement of Rosuvastatin Calcium by Liquisolid Compact Technique

In present investigation liquisolid compact technique is investigated as a tool for enhanced dissolution of poorly water-soluble drug Rosuvastatin calcium (RVT). The model drug RVT, a HMG-Co A reductase inhibitor was formulated in form of directly compressed tablets and liquisolid compacts; and studied for in-vitro release characteristics at different dissolution conditions. In this technique, liquid medications of water insoluble drugs in non-volatile liquid vehicles can be converted into acceptably flowing and compressible powders. Formulated systems were assessed for precompression parameters like flow properties of liquisolid system, Fourior transform infra red spectra (FTIR) analysis, X-ray powder diffraction (XRPD), differential scanning calorimetry (DSC), and post compression parameters like content uniformity, weight variation, hardness and friability, disintegration test, wetting time, in vitro dissolution studies, effect of dissolution volume on drug release rate, and estimation of fraction of molecularly dispersed drug in liquid medication. As liquisolid compacts demonstrated significantly higher drug release rates, we lead to conclusion that it could be a promising strategy in improving the dissolution of poor water soluble drugs and formulating immediate release solid dosage forms.

New formulation approaches to improve solubility and drug release from fixed dose combinations: case examples pioglitazone/glimepiride and ezetimibe/simvastatin

Low aqueous solubility is often a limiting aspect to the bioavailability of poorly soluble, but highly permeable drugs (class II compounds according to the Biopharmaceutics Classification System - BCS) administered in single drug products or as fixed dose combinations. The aim of the present series of experiments was to improve the solubility and dissolution of two fixed dose combination formulations (FDC), each consisting of two BCS class II drugs. The first FDC contained a weak acid (glimepiride) and a weak base (pioglitazone), while the second FDC contained two compounds (simvastatin and ezetimibe) that are essentially non-ionised over the physiological pH range. The formulation approaches used were as follows: (a) an inclusion complex with hydroxypropyl-β-cyclodextrin (HP-β-CD), (b) a solid dispersion with Soluplus, a new highly water soluble polyvinyl caprolactam - polyvinyl acetate - polyethylene glycol graft copolymer and (c) a ternary inclusion complex with both HP-β-CD and Soluplus. Solid state analysis was performed for the pure drugs, and all formulations using powder X-ray diffraction (PXRD). The in vitro performance of the different formulation approaches, as gauged by solubility and dissolution experiments, was compared with that of the marketed products containing the respective fixed dose combinations, Tandemact 30 mg/4 mg tablets and Inegy 10 mg/40 mg tablets. The FDCs of the pure drugs and the marketed products showed very poor (and especially for pioglitazone, strongly pH-dependent) dissolution. By contrast, all binary and ternary inclusion complexes showed enhanced release for both drugs in the FDC. The ternary inclusion complex generated synergistic improvement in solubility and dissolution results for both FDCs. For example, in pH conditions of the fasted small intestine after a test duration of 240 min, we observed 100% dissolution of both drugs from the ternary pioglitazone/glimepiride (30 mg/4 mg) complex formulation, whereas from the marketed formulation less than 5% pioglitazone, and only 25% glimepiride dissolved. Using the same conditions, 60% ezetimibe and 85% simvastatin dissolved from the ternary ezetimibe/simvastatin (10 mg/40 mg) complex formulation, whereas with less than 5% ezetimibe and 10% simvastatin dissolved after 240 min, the marketed FDC formulation showed poor dissolution. Based on the results of the present study, the bioavailability of both drugs in the fixed dose combination is likely to be increased after oral administration of the new formulations, especially when the fixed dose combination is formulated as a ternary complex consisting of HP-β-CD and Soluplus.

A pilot human pharmacokinetic study and influence of formulation factors on orodispersible tablet incorporating meloxicam solid dispersion using factorial design

Meloxicam (MLX) suffers from poor aqueous solubility leading to slow absorption following oral administration; hence, immediate release MLX tablet is unsuitable in the treatment of acute pain. This study aims to overcome such a drawback by increasing MLX solubility and dissolution using PEG solid dispersion (SD), then, to investigate the feasibility of incorporating the SD into orodispersible tablets (ODTs). A 2(3) full factorial design was employed to investigate the influence of three formulation variables on MLX ODTs. The selected factors: camphor (X(1)) as pore-forming material, and croscarmellose sodium (X(2)) as superdisintegrant, showed significant positive influence, while PEG content (X(3)) was proved to negatively affect both disintegration and wetting times. In addition, isomalt increased disintegration and wetting times when compared to mannitol as diluents. The pharmacokinetic assessment of the optimum ODT formulation in healthy human subjects proved that the faster MLX dissolution by using PEG solid dispersion at pH 6.8 resulted in more rapid absorption of MLX. The rate of absorption of MLX from ODT was significantly faster (p = 0.030) with a significantly higher peak plasma concentration (P = 0.037) when compared to the marketed immediate release MLX tablet with a mean oral disintegration time of 17 ± 3 s.

Solid dispersions as strategy to improve oral bioavailability of poor water soluble drugs

Solid dispersions are one of the most promising strategies to improve the oral bioavailability of poorly water soluble drugs. By reducing drug particle size to the absolute minimum, and hence improving drug wettability, bioavailability may be significantly improved. They are usually presented as amorphous products, mainly obtained by two major different methods, for example, melting and solvent evaporation. Recently, surfactants have been included to stabilize the formulations, thus avoiding drug recrystallization and potentiating their solubility. New manufacturing processes to obtain solid dispersions have also been developed to reduce the drawbacks of the initial process. In this review, it is intended to discuss the recent advances related on the area of solid dispersions.

Preparation, Characterization and In vitro Dissolution Studies of Solid Dispersion of Meloxicam with PEG 60001)

The poor solubility and wettability of meloxicam leads to poor dissolution and hence showing variations in bioavailability. The present study is aimed to increase solubility and dissolution of the drug using solid dispersion techniques. The solid binary systems were prepared at various drug concentrations (5-40%) with polyethylene glycol 6000 by different techniques (physical mixing, solvent evaporation). The formulations were characterized by solubility studies, differential scanning calorimetry, fourier transform infrared spectroscopy and in vitro dissolution rate studies. The solubility of drug increased linearly with increase in polymer concentration showing A(L) type solubility diagrams. Infrared spectroscopy studies indicated the possibility of hydrogen bonding with polymer. The differential scanning calorimetry and powder X ray diffraction demonstrated the presence of polymer as eutectica or monotectica in solid dispersion along with the physical characteristics of the drug (crystalline, amorphous or a mixture of both). The solid dispersions of the drug demonstrated higher drug dissolution rates than physical mixtures and pure meloxicam, as a result of increased wettability and dispersibility of drug in a solid dispersion system.

Effect of hydrogen bonding interactions on the release mechanism of felodipine from nanodispersions with polyvinylpyrrolidone

Solid dispersion systems are widely investigated for the dissolution enhancement of poorly water soluble drugs. Nevertheless, very limited commercial use has been achieved due to the poor predictability of such systems caused by the lack of a basic understanding of the dissolution optimization mechanism. In the present study an investigation of the release mechanism is performed for solid dispersion systems composed by polyvinylpyrrolidone (PVP) and felodipine (FEL), based on a correlation of their hydrophilicity with the intensity of interactions. The existing interactions were evaluated by using NMR and UV spectroscopy while molecular simulation techniques were also enabled. It was found that the interactions that take place correspond to the creation of hydrogen bonds. The correlation between the intensity of interactions and the concentration of PVP in the matrix showed a sigmoid function. The interactions are impressively increased for polymer concentration exceeding 75% (w/w). This phenomenon was well explained by using the molecular simulation technique. A similar sigmoid pattern was found for the function between dissolution profiles and polymer concentration in the matrix, indicating that the intensity of interactions promotes the dissolution enhancement. Investigation of the solubility and the particle size distribution of FEL in the binary system appeared to have similar behaviour indicating that the interactions affect the release profile through these two factors. The hydrophilicity of PVP does not significantly affect this enhancement as the contact angle was found to be linear to PVP concentration. Microscopic observation of the dissolution behaviour showed that FEL remains in fine dispersion in aqueous solution, verifying the release mechanism.

Microcalorimetric studies to determine the enthalpy of solution of diclofenac sodium, paracetamol and their binary mixtures at 310.15 K

A sensitive and selective microcalorimetric technique has been used to determine the enthalpy of solution of diclofenac sodium (DS), paracetamol (PC) and their binary mixtures over a wide range of composition in the pH range 4-12. The systems showed endothermic behavior. The molar enthalpies of solutions of DS vary between 42.26+/-0.16 and 50.48+/-0.03 kJ mol(-1) at pH 4-9 and for PC from 24.28+/-0.05 to 36.03+/-0.01 kJ mol(-1) at pH 5-12. The excess molar enthalpy of their mixtures has also been determined. The values of excess molar enthalpy of solutions are negative and very low in magnitude indicating no specific interaction between DS and PC in solution.

Stabilization of amorphous indomethacin by co-grinding in a ternary mixture

Mechanochemical amorphization of indomethacin (IM) was substantially enhanced by grinding with SiO(2), talc and a Mg(OH)(2)-SiO(2) mixture. The rates of the mechanochemical amorphization were in the order of Mg(OH)(2)-SiO(2) mixture>talc>SiO(2). Amorphous state stability of IM compounded with the carrier was examined by crystallization behavior under the condition of 30 degrees C and 11% relative humidity. Superiority of the binary mixture as a carrier was explained in terms of the mechanically induced strong acidic sites of the carrier.

The mechanisms of drug release from solid dispersions in water-soluble polymers

Solid dispersions in water-soluble carriers have attracted considerable interest as a means of improving the dissolution rate, and hence possibly bioavailability, of a range of hydrophobic drugs. However, despite the publication of numerous original papers and reviews on the subject, the mechanisms underpinning the observed improvements in dissolution rate are not yet understood. In this review the current consensus with regard to the solid-state structure and dissolution properties of solid dispersions is critically assessed. In particular the theories of carrier- and drug-controlled dissolution are highlighted. A model is proposed whereby the release behaviour from the dispersions may be understood in terms of the dissolution or otherwise of the drug into the concentrated aqueous polymer layer adjacent to the solid surface, including a derivation of an expression to describe the release of intact particles from the dispersions. The implications of a deeper understanding of the dissolution mechanisms are discussed, with particular emphasis on optimising the choice of carrier and manufacturing method and the prediction of stability problems.