Mechanisms underlying changes in indomethacin solubility with local anesthetics and related basic additives

Quantification of crystallinity during indomethacin crystalline transformation from α- to γ-polymorphic forms and of the thermodynamic contribution to dissolution in aqueous buffer and solutions of solubilizer

The thermodynamic properties and dissolution of indomethacin (INM) were analyzed as models for poorly water-soluble drugs. Physical mixtures of the most stable γ-form and metastable α-form of INM at various proportions were prepared, and their individual signal intensities proportional to their mole fractions were observed using X-ray powder diffraction and Fourier transform infrared spectrometry at standard temperature. The endothermic signals of the α-form, with a melting point of 426 K, and that of the γ-form, with a melting point of 433 K, were obtained by differential scanning calorimetry (DSC). Furthermore, an exothermic DSC peak of the α/γ-phase transition at approximately 428 K was obtained. As we computed the melting entropy of the α-form and that of its transformation, the frequency of the transition was quantitatively determined, which indicated the maximum of the α/γ-phase transition at an α-form proportion of 68%. Subsequently, the thermodynamic contributions of the α- and γ-forms were analyzed using a Van't Hoff plot for solubility in aqueous solutions at pH 6.8. The dissolution enthalpies for α- and γ-forms were 28.2 and 31.2 kJ mol-1, respectively, which are in agreement with the quantitative contribution predicted by the product of the temperature and melting entropy. The contribution of melting entropy was conserved in different dissolution processes with aqueous solvents containing lidocaine, diltiazem, l-carnosine, and aspartame as solubilizers; their γ-form Setschenow coefficients were -39.6, +82.9, -17.3, and +23.2, whereas those of the α-form were -39.7, +80.4, -16.7, and +22.7, respectively. We conclude that the dissolution ability of the solid state and solubilizers indicate their additivity independently.

Using singular value decomposition to analyze drug/β-cyclodextrin mixtures: insights from X-ray powder diffraction patterns

The article discusses the use of mathematical models and linear algebra to understand the crystalline structures and interconversion pathways of drug complexes with β-cyclodextrin (β-CD). It involved the preparation and analysis of mixtures of indomethacin, diclofenac, famotidine, and cimetidine with β-CD using techniques such as differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD), and proton nuclear magnetic resonance (1H-NMR). Singular value decomposition (SVD) analysis is used to identify the presence of different polymorphs in the mixtures of these drugs and β-CD, determine interconversion pathways, and distinguish between different forms. In general, linear algebra or artificial intelligence (AI) is used to approximate the contribution of distinguishable entities to various phenomena. We expected linear algebra to completely reveal all eight entities present in the diffractogram dataset. However, after performing the SVD procedure, we found that only six independent basis functions were extracted, and the entities of the INM α-form and the CIM B-form were not included. It is considered that this is due to that data processing is limited to revealing only six or seven independent factors, as it is a small world. The authors caution that these may not always reproduce or approach reality in complicated real-world situations.

Optimization of the stability constants of the ternary system of diclofenac/famotidine/β-cyclodextrin by nonlinear least-squares method using theoretical equations

This study aimed to establish a new method for determining the stability constants of drug/β-cyclodextrin (β-CD) complexes when multiple drugs interacting with each other coexist in the solution of complexation. The basic drug famotidine (FAM) and the acidic drug diclofenac (DIC) were used as model drugs, their solubility decreasing owing to their mutual interaction. The dissolution of both FAM and DIC was characterized by A_L-type phase solubility diagrams in the presence of the other's 1:1 complex with β-CD. When the stability constant was calculated from the slope of the phase solubility diagram using the conventional phase solubility diagram method, it was modified in the presence of the other drug. However, by performing optimization calculations that considered the interactions between the drug/β-CD complex and the drug, drug/β-CD complexes, and drugs, we were able to accurately calculate the stability constant of DIC/β-CD and FAM/β-CD complexes even in the presence of FAM and DIC, respectively. The results of the solubility profile indicated that various molecular species, which are attributed to drug-drug and drug/β-CD interactions, interfere with the values of the dissolution rate constants and saturated concentration in the solubility profiles.

Stereomicroscope with Imaging Analysis: A Versatile Tool for Wetting, Gel Formation and Erosion Rate Determinations of Eutectic Effervescent Tablet

Wettability, gel formation and erosion behaviors could influence the drug release pattern of solid dosage forms. Typically, these parameters are evaluated using a variety of techniques. Nonetheless, there has been no previous research on versatile tool development for evaluating several tablet characteristics with a single tool. The aim of this study was to develop the versatile tool for measuring various physical properties of eutectic effervescent tablets and also investigate the relationship between these parameters with parameters from drug dissolution. Ibuprofen (IBU)-poloxamer 407 (P407) eutectic effervescent tablets were fabricated with a direct compression method. Their wetting properties, gel formation and erosion behaviors were investigated using a stereomicroscope with imaging analysis in terms of the liquid penetration distance, gel thickness and erosion boundary diameter, respectively. In addition, the dissolution rate (k) and disintegration time of eutectic effervescent tablets in 0.1 N HCl buffer pH 1.2 were also determined. Incorporation of P407 into the IBU tablet improved the tablet wetting properties with increasing liquid penetration distance under stereoscope. CO2 liberation from effervescent agents promoted tablet surface roughness from matrix erosion. The relationship between observed physical properties and disintegration and dissolution parameters suggested that the combination of erosion by effervescent agents and gel formation by P407 had a potential influence on dissolution enhancement of the formulation. Therefore, a developed stereomicroscope with an imaging analysis technique was exhibited as an alternative versatile tool for determining the wetting properties, gel formation and erosion behaviors of pharmaceutical solid dosage forms.

Enthalpy-Entropy Compensation in the Structure-Dependent Effect of Nonsteroidal Anti-inflammatory Drugs on the Aqueous Solubility of Diltiazem

Certain combinations of acidic and basic drugs can cause significant changes in physicochemical properties through the formation of ionic liquids, eutectic mixtures, or deep eutectic solvents. In particular, combining indomethacin and lidocaine is known to result in apparent increases in both the partition coefficients (hydrophobicity) and aqueous solubilities (hydrophilicity). The physicochemical interactions between drugs change the water solubility of the drugs and affect the bio-availability of active pharmaceutical ingredients. Therefore, we need to clarify the mechanism of changes of water solubility of drugs through the physicochemical interactions. In the present study, we identified a thermodynamic factor that regulates the dissolution of a basic drug, in the presence of various acidic nonsteroidal anti-inflammatory drugs. The results demonstrated that enthalpy-entropy compensation plays a key role in the dissolution of drug mixtures and that relevant thermodynamic conditions should be considered.

Eutectic mixtures as an approach to enhance solubility, dissolution rate and oral bioavailability of poorly water-soluble drugs

Eutectic mixtures have been known for a long time in the pharmaceutical field. However, its potential as a system to improve the solubility and dissolution of poorly water-soluble drugs remains little explored. Studies involving the microstructural characterization and the preparation of solid dosage forms containing eutectic mixtures are also an issue to be developed. Recently, the number of studies involving the preparation of eutectic mixtures to improve the solubility and oral bioavailability of poorly soluble drugs has increased considerably, including drug-carrier and drug-drug mixtures. In this review is discussed the potential of eutectic mixtures as an alternative pharmaceutical solid system to enhance drugs solubility, dissolution rate or oral bioavailability. Different aspects like history, physico-chemical, microstructural properties, preparation methods, mechanisms involved in solubility/dissolution enhancement, techniques for solid state characterization, in vivo studies, advantages, limitations and formulation perspective are also discussed.

The function of oxybuprocaine: a parachute effect that sustains the supersaturated state of anhydrous piroxicam crystals

Polymers have been recognized to have the function of sustaining the supersaturated state of drugs. This function has been widely studied because it will improve the absorption of poorly water-soluble drugs. However, clarifying the mechanism of this sustaining pharmaceutical effect (parachute effect) on the supersaturated state as a result of polymers is remains a task. We have found that oxybuprocaine, which is a small molecule, has a parachute effect on the supersaturated state (due to an anhydrate-to-hydrate transformation) of piroxicam-anhydrate in the aqueous phase. We consider that oxybuprocaine controls the environment of the solution and the network of polymers is unnecessary. Therefore, oxybuprocaine not only becomes a clue for elucidating the essential mechanism of the parachute effect of polymers but also enables us to rationally propose a new type of solubilizer.

A small molecule, oxybuprocaine, has a parachute effect on the supersaturated state of piroxicam anhydrous crystals.

Sketching neoteric solvents for boosting drugs bioavailability

Emerging neoteric solvents are being the subject of growing attention due to their lower cost and environmental impact, so they are being applied in a broad spectrum of industries. Among them, the pharmaceutical sector is demanding new environmentally friendly and non-toxic solvents able to enhance drugs solubility and stability. The introduction of ionic liquids turned out to be a breakthrough in the field of Green Chemistry opening up new separation and catalysis opportunities. In this sense, the options represented by Deep Eutectic Solvents make up an attractive alternative due to the low cost of their raw material, simple synthesis, and eco-friendly character. In line with these findings, Therapeutic Deep Eutectic Solvents and Natural Deep Eutectic Solvents are new and promising alternatives to improve the bioavailability of drugs in pharmaceutical formulations. This leading article is focused on providing a general picture of the advantages and drawbacks of these new solvents as well as the main research lines and perspectives to achieve efficient drugs delivery systems.

How tenofovir disoproxil fumarate can impact on solubility and dissolution rate of efavirenz?

Efavirenz (EFZ) and tenofovir disoproxil fumarate (TDF) can be used simultaneously in the treatment of human immunodeficiency virus type1 infection. In this work the impact of TDF, a hydrophilic drug, on the solubility and dissolution rate of EFZ, a poorly water-soluble drug, was evaluated. EFZ/TDF binary mixtures in different molar ratios were prepared. Differential scanning calorimetry (DSC) results indicate the formation of a eutectic mixture, the molar ratio of 65/35 being the eutectic point. It was observed an increase in the EFZ solubility in water and acidic conditions (0.1 N HCl and biorelevant medium), in the presence of TDF. On the other hand, there was a decreasing on EFZ solubility in phosphate buffer pH 6.8, probably influenced by the lower solubility of TDF in this medium. The high solubility of TDF in water and acidic medium may have contributed to improve the solubility of EFZ, as well as the formation of a eutectic mixture, supported by X-ray powder diffraction (XRPD) and Fourier Transform infrared spectroscopy (FTIR) analyses. However, TDF solubility and dissolution rate was not significantly influenced by the presence of EFZ.