Effects of phosphate on drug solubility behavior of mixture ibuprofen and lidocaine

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.

Effect of Cyclodextrin Complex Formation on Solubility Changes of Each Drug Due to Intermolecular Interactions between Acidic NSAIDs and Basic H2 Blockers

One of the solubilization of poorly water-soluble drugs is the use of cyclodextrin (CD)-based inclusion complexes. On the other hand, few studies have investigated how CD functions on the solubility of drugs in the presence of multiple drugs that interact with each other. In this study, we used indomethacin (IND) and diclofenac (DIC) as acidic drugs, famotidine (FAM) and cimetidine (CIM) as basic drugs, and imidazole (IMZ), histidine (HIS), and arginine (ARG) as compounds structurally similar to basic drugs. We attempted to clarify the effect of β-CD on the solubility change of each drug in the presence of multiple drugs. IND and DIC formed a eutectic mixture in the presence of CIM, IMZ, and ARG, which greatly increased the intrinsic solubility of the drugs as well as their affinity for β-CD. Furthermore, the addition of high concentrations of β-CD to the DIC-FAM combination, which causes a decrease in solubility due to the interaction, improved the solubility of FAM, which was decreased in the presence of DIC. These results indicate that β-CD synergistically improves the solubility of drugs in drug-drug combinations, where the solubility is improved, whereas it effectively improves the dissolution rate of drugs in situations where the solubility is reduced by drug-drug interactions, such as FAM-DIC. This indicates that β-CD can be used to improve the physicochemical properties of drugs, even when they are administered in combination with drugs that interact with each other.

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.

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.

Saturated adsorption of lidocaine and coal tar dyes onto porous polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) has excellent physical properties and has been used in a wide range of applications in various fields. Adsorption research on PTFE is essential as primary research for the further application of PTFE. We attempted to adsorb coal tar dyes and model drugs such as lidocaine onto PTFE as a guideline to search for medicines that adsorb onto PTFE. Saturation curves were obtained after analyzing the adsorption of coal tar dyes on PTFE using the Hanes-Woolf plot. In addition, we collected multiple cases of ATR-FTIR spectral changes and/or retention depending on TPM derivatives and other adsorbates. Lidocaine matched some coal tar dye for the apparent spectral changes between the adsorbed molecules and its crystalline powder. The apparent spectral changes are blue-shifted, suggesting a hydrophobic interaction between the dyes/lidocaine and porous PTFE. This work provides a promising strategy for further application of PTFE.

Therapeutic Liquid Formulations Based on Low Transition Temperature Mixtures for the Incorporation of Anti-Inflammatory Drugs

Most nonsteroidal anti-inflammatory drugs (NSAIDs) present poor aqueous solubility, impairing their efficiency in physiological media. In this context, Low Transition Temperature Mixtures (LTTMs) are a promising platform to overcome drugs' poor solubility, forming therapeutic liquid formulations. In this work, the LTTMs of citric acid:L-arginine:water (C:A:W) and glycerol:sorbitol (G:S) were studied in terms of their features and assessed in terms of their ability to increase the solubility of six NSAIDs in physiological media. The physicochemical properties of LTTMs were characterized by state-of-art techniques commonly used for these systems. The cytotoxicity of G:S was also evaluated in L929 mouse fibroblasts and the viscosity, polarity, and pH properties of the studied mixtures were related to the solubility of NSAIDs. The pH and polarity were the parameters that most influenced the drugs' solubility. Ibuprofen, naproxen, ketoprofen, indomethacin, and flurbiprofen did not present any solubility improvement in the formulations tested. However, concentrated mixtures of C:A:W or G:S in the physiologic-mimicked media (PBS) rendered a celecoxib solubility 4 and 5 times higher than PBS, respectively. These therapeutic liquid formulations of celecoxib in C:A:W or G:S can be a promising tool to increase celecoxib's therapeutic efficiency in local applications.

Stabilization of the Metastable α-Form of Indomethacin Induced by the Addition of 2-Hydroxypropyl-β-Cyclodextrin, Causing Supersaturation (Spring) and Its Sustaining Deployment (Parachute)

The purpose of this study is to find that a small amount of 2-Hydroxypropyl-β-cyclodextrin (HP-β-CD) can produce a parachute effect on indomethacin (INM). From the examination of dissolution curves and concentration after several days, the supersaturation of INM was observed for the mixtures containing HP-β-CD at a molar ratio ≤ 0.5, and the sustained deployment of supersaturation was found not only in equimolar mixtures but also in mixtures with a shortage of HP-β-CD. In the solid state, it was compared the physical properties of INM/HP-β-CD mixtures using two different mixing methods and determined the stoichiometry of INM and HP-β-CD. Differential scanning calorimetry (DSC) revealed that the polymorphs of INM were converted by HP-β-CD into an amorphous state. Furthermore, X-ray powder diffraction (XRPD) and DSC-XRPD demonstrated that INM crystals from the INM/HP-β-CD mixture prepared from an EtOH solution were metastable. In conclusion, these phenomena may be considered the "spring" and "parachute" effects of mixtures with a shortage of HP-β-CD, as they depended on the presence of the metastable α-form of INM. The addition of 1/3 to 1/20 equivalents of HP-β-CD to INM enhanced INM solubility.

Molecular recognizable ion-paired complex formation between diclofenac/indomethacin and famotidine/cimetidine regulates their aqueous solubility

This study focused on the physicochemical interactions between acidic and basic drugs in aqueous solutions. Their ion pair interactions were evaluated in an in vitro study. The model non-steroid anti-inflammatory drugs (NSAIDs), indomethacin (INM) and diclofenac (DIC), were used as acidic and hydrophobic drugs, whereas cimetidine (CIM), famotidine (FAM), and imidazole (IMD) were used as basic additives with heterocyclic moieties. The drug mixtures were evaluated by thermal analysis, dissolution test, nuclear magnetic resonance (NMR) spectroscopy, and mass spectroscopy. The fusion enthalpy of DIC-CIM, INM-CIM, and INM-arginine (ARG) sample was calculated based on melting temperature transformation. The DIC mixture with CIM, IMD, antipyrine (ANT), and ARG showed enhanced solubility, whereas the DIC-FAM mixture sample showed a decreased solubility. Electrospray ionization mass spectroscopy was carried out to detect binary mixtures. The interactions in DIC-FAM mixture sample were found between the carboxyl group of DIC and the amine groups of FAM by NMR. These findings were suggested that DIC-FAM mixture samples construct ion pair complexes based on the theory of Bjerrum. Moreover, the acid model drug and basic model drug also can be constructed 1:1 complexes that affects their solubility in the solvent of water type.

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.