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Pyrazinamide is a first line drug used for the treatment of tuberculosis, a pathology that caused the death of more than 1.3 million people in the world during 2022, according to WHO, being a drug of current interest due to its relevance in pharmaceutical and medical sciences. In this context, solubility is one of the most important physicochemical parameters in the development and/or optimization of new pharmaceutical forms, so the present work aims to present a thermodynamic study of the solubility of pyrazinamide in nine organic solvents of pharmaceutical interest. Using the shake-flask method and UV/Vis spectrophotometry, the solubility of this drug was determined at 9 temperatures; the maximum solubility was obtained in dimethyl sulfoxide at 318.15 K ( x 2 = 0.0816 ± 0.004 ) and the minimum in cyclohexane at 283.15 K ( 1.73 ± 0.05 × 10 − 5 ). From the apparent solubility data, the thermodynamic functions of solution and mixing were calculated, indicating an endothermic process. In addition, the solubility parameter of pyrazinamide was calculated using the Hoftyzer-van Krevelen (32.90 MPa1/2) and Bustamante (28.14 MPa1/2) methods. The maximum solubility was reached in dimethyl sulfoxide and the minimum in cyclohexane. As for the thermodynamic functions, the entropy drives the solution process in all cases. In relation to the solubility parameter, it can be analyzed that the mathematical models offer approximations; however, the experimental data are still primordial at the time of inferring any process. [ABSTRACT FROM AUTHOR]

In the current work, the performance of the shake-flask and laser monitoring-based techniques for the determination of the solubility is described as a video file. The video is prepared in three parts. The first part is a general explanation of solubility and its manual and automatic measurement methods. The second part is about how to perform the shake-flask method to measure drug solubility, and the third part is about how the laser monitoring -based automatic device works to measure drug solubility.

Pyrazinamide is a first line drug used for the treatment of tuberculosis, a pathology that caused the death of more than 1.3 million people in the world during 2022, according to WHO, being a drug of current interest due to its relevance in pharmaceutical and medical sciences. In this context, solubility is one of the most important physicochemical parameters in the development and/or optimization of new pharmaceutical forms, so the present work aims to present a thermodynamic study of the solubility of pyrazinamide in nine organic solvents of pharmaceutical interest. Using the shake-flask method and UV/Vis spectrophotometry, the solubility of this drug was determined at 9 temperatures; the maximum solubility was obtained in dimethyl sulfoxide at 318.15 K (x2=0.0816±0.004) and the minimum in cyclohexane at 283.15 K (1.73±0.05×10−5). From the apparent solubility data, the thermodynamic functions of solution and mixing were calculated, indicating an endothermic process. In addition, the solubility parameter of pyrazinamide was calculated using the Hoftyzer-van Krevelen (32.90 MPa1/2) and Bustamante (28.14 MPa1/2) methods. The maximum solubility was reached in dimethyl sulfoxide and the minimum in cyclohexane. As for the thermodynamic functions, the entropy drives the solution process in all cases. In relation to the solubility parameter, it can be analyzed that the mathematical models offer approximations; however, the experimental data are still primordial at the time of inferring any process.

In the present study, various procedures have been compared for the determination of lipophilicity, hydrophobicity, and plasma protein binding of curcuminoids, boswellic acids, andrographolides, and piperine as biologically active ingredients of botanicals used in IBD treatment. Our results have shown that IAM-HPLC assay is the most suitable one for lipophilicity determination of all analytes regardless of their class and botanical source. HSA-HPAC and AGP-HPAC assays revealed that all investigated compounds have a higher affinity for HSA which is the most abundant protein in human plasma. The high affinity of biologically active compounds to all biological structures (phospholipids and proteins) admonishes that their small portion is available for therapeutic effects in IBD patients. Our experimental research is complemented by various theoretical approaches based on different algorithms for pharmacokinetic properties prediction. The similarities between experimental and calculated values were evaluated using PCA and CA as a statistical tool. The statistical analysis implies that plasma protein binding is a complex process, and theoretical approaches still cannot fully replace experimental ones. [ABSTRACT FROM AUTHOR]

In the present study, various procedures have been compared for the determination of lipophilicity, hydrophobicity, and plasma protein binding of curcuminoids, boswellic acids, andrographolides, and piperine as biologically active ingredients of botanicals used in IBD treatment. Our results have shown that IAM-HPLC assay is the most suitable one for lipophilicity determination of all analytes regardless of their class and botanical source. HSA-HPAC and AGP-HPAC assays revealed that all investigated compounds have a higher affinity for HSA which is the most abundant protein in human plasma. The high affinity of biologically active compounds to all biological structures (phospholipids and proteins) admonishes that their small portion is available for therapeutic effects in IBD patients. Our experimental research is complemented by various theoretical approaches based on different algorithms for pharmacokinetic properties prediction. The similarities between experimental and calculated values were evaluated using PCA and CA as a statistical tool. The statistical analysis implies that plasma protein binding is a complex process, and theoretical approaches still cannot fully replace experimental ones.

Abstract Lipophilicity of the compounds is useful to (i) explain their distribution in biological systems, which is different in plant and in animal organisms, (ii) predict the possible pathways of pollutant transport in the environment, and (iii) support drug discovery process and select optimal composition in terms of bioactivity and bioavailability. The lipophilic properties can be determined by two main approaches, experimental, which apply instrumental techniques or computational, which is based on the complex algorithms. This review focuses primarily on various analytical methods that are used in the lipophilicity measurements. The classical methods and others based on chromatographic, electroanalytical and electroseparation approaches are compared and described in details. Modern solutions with chromatographic systems and their practical applications in the measurements of lipophilic and biomimetic properties of compounds have been included. However, there is an urgent need to standardize the high-throughput and reliable analytical procedure of the evaluation of lipophilic properties. Highlights • The role of lipophilicity in biological, environmental and technical science. • Lipophilicity assessment using classical and modern approaches. • Advantages and limitations of methods of lipophilicity determination. • Novel solutions in chromatographic methods used for lipophilicity determination. [ABSTRACT FROM AUTHOR]

Aims: The aqueous solubility of two polymorphic forms of venlafaxine hydrochloride was investigated. Methods: The pH-dependent solubility (SpH) over a wide pH range was measured by saturation shake-flask (SSF) method at 25 °C. The solubility of the free base form was depicted by the intrinsic solubility (So). To identify the solid form present at the solubility equilibrium, X-ray powder diffraction (XRPD) and Raman spectroscopy was carried out. The dissolution was studied using real time concentration monitoring applying fiber optic UV probes. Results: No difference was found in the SpH values of Form I and Form II, in the pH range 7.5-12. Solid phase isolated from pH 10-12 suspensions was identified as free base by XRPD and Raman spectroscopy. Precipitates separated from pH 7-8 samples were also identical product. The transition of polymorphs to the free base was supported by the real time dissolution analysis. Conclusion: In this study we demonstrated a good agreement of equilibrium solubility measured by SSF method and in-situ UV fiber optic method. µDISS Profiler™ has the advantage to provide much more information about dissolution process; with this approach the dissolution kinetic, the supersaturation and the time needed to reach the equilibrium can be easily monitored. [ABSTRACT FROM AUTHOR]

This study aimed at evaluating the shake-flask use as a universal method to evaluate drug solubility in a biowaiver context as proposed by FDA, EMA and ANVISA. The solubility of losartan was determined in three buffers using the shake-flask method, intrinsic dissolution (ID) and Quantum Chemistry. Moreover, the evaluation of a losartan dissolution profile from coated tablets was conducted. The losartan low solubility in pH 1.2 and high solubility in pH 6.8 were observed using the shake-flask method. However, the solubility results using ID demonstrated its high solubility in pH 1.2 and 6.8. It was not possible to find conclusive results regarding the solubility of the drug in pH 4.5. The studies conducted by Quantum Chemistry provide molecular and electronic data that helped understand the losartan solvation in different pH values. Our experimental results defined that losartan can be classified as a low-solubility drug. In addition, this work shows that shake-flask cannot be a universal method of solubility studies in biowaiver context. Individual analysis will be necessary. The intrinsic dissolution should be considered as a complementary method. [ABSTRACT FROM AUTHOR]

Abstract The phase separation is a crucial step in equilibrium solubility measurements. In the standardized protocol of saturation shake-flask method, sedimentation is proposed as the safest technique. However filtration is widely used in pharma practice. In this paper the effect of the filtration on the measured equilibrium solubility results is presented. The equilibrium solubility values of four model compounds, namely diclofenac sodium, hydrochlorothiazide, papaverine hydrochloride and progesterone were determined at various pH values using the saturation shake-flask method. Two phase separation techniques (sedimentation and filtration) were applied for the separation of the solid from the saturated solution. Four membrane filters, polyvinylidene fluoride (PVDF), polyether sulfone (PES), polytetrafluoroethylene (PTFE) and nylon, as well as an analytical filter paper were investigated. The results obtained by filtration were compared with those measured by sedimentation and the distortion effect of the filter (DEF) on solubility results was expressed in %. The results showed that the filter material type is able to remarkably influence the results in solubility measurements. In several cases, the significant adsorption to the filter caused high inaccuracy in the measured concentration value, more over in some cases failed to work at all. As a main conclusion of this work, if the step of filtration is inevitable, the adsorption to the filter can be mitigated with the appropriate filter type selection what needs some experiences and knowledge about the acid-base chemistry and polar/apolar nature of the sample. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

The ionization constants ( pK a ) and the pH-dependent solubility (log S -pH) of six phenothiazine derivatives (promazine hydrochloride, chlorpromazine hydrochloride, triflupromazine hydrochloride, fluphenazine dihydrochloride, perphenazine free base, and trifluoperazine dihydrochloride) were determined at 25 and 37 °C. The pK a values of these low-soluble surface active molecules were determined by the cosolvent method ( n -propanol/water at 37 °C and methanol/water at 25 °C). The log S -pH profiles were measured at 24 h incubation time in 0.15 M phosphate buffers. The log S-pH “shape-template” method, which critically depends on accurate pK a values (determined independently of solubility data), was used to propose speciation models, which were subsequently refined by rigorous mass-action weighted regression procedure described recently. Differential scanning calorimetry (DSC), UV–visible spectrophotometry, potentiometric, and high performance liquid chromatography (HPLC) measurements were used to characterize the compounds. The intrinsic solubility ( S 0 ) values of the three least-soluble drugs (chlorpromazine·HCl, triflupromazine·HCl, and trifluoperazine·2HCl) at 25 °C were 0.5, 1.1, and 2.7 μg/mL (resp.). These values increased to 5.5, 9.2, and 8.7 μg/mL (resp.) at the physiological temperature. The enthalpies of solution for the latter compounds were exceptionally high positive (endothermic) values (99–152 kJ·mol − 1 ). Cationic sub-micellar aggregates were evident (from the distortions in the log S-pH profiles) for chlorpromazine, fluphenazine, perphenazine, and trifluoperazine at 25 °C. The effects persisted at 37 °C for chlorpromazine and trifluoperazine. The solids in suspension were apparently amorphous in cases where the drugs were introduced as the chloride salts. [ABSTRACT FROM AUTHOR]

The established methods to predict drug-polymer solubility at room temperature either rely on extrapolation over a long temperature range or are limited by the availability of a liquid analogue of the polymer. To overcome these issues, this work investigated a new methodology where the drug-polymer solubility is estimated from the solubility of the drug in a solution of the polymer at room temperature using the shake-flask method. Thus, the new polymer in solution method does not rely on temperature extrapolations and only requires the polymer and a solvent, in which the polymer is soluble, that does not affect the molecular structure of the drug and polymer relative to that in the solid state. Consequently, as this method has the potential to provide fast and precise estimates of drug-polymer solubility at room temperature, we encourage the scientific community to further investigate this principle both fundamentally and practically. [ABSTRACT FROM AUTHOR]

A high-throughput method for determining the octanol/water partition coefficient ( P o/w ) of a large variety of compounds exhibiting a wide range in hydrophobicity was established. The method combines a simple shake-flask method with a novel two-phase solvent system comprising an acetonitrile–phosphate buffer (0.1 M, pH 7.4)—1-octanol (25:25:4, v/v/v; AN system). The AN system partition coefficients ( K AN ) of 51 standard compounds for which log P o/w (at pH 7.4; log D ) values had been reported were determined by single two-phase partitioning in test tubes, followed by measurement of the solute concentration in both phases using an automatic flow injection-ultraviolet detection system. The log K AN values were closely related to reported log D values, and the relationship could be expressed by the following linear regression equation: log D = 2.8630 log K AN  –0.1497( n = 51). The relationship reveals that log D values (+8 to –8) for a large variety of highly hydrophobic and/or hydrophilic compounds can be estimated indirectly from the narrow range of log K AN values (+3 to –3) determined using the present method. Furthermore, log K AN values for highly polar compounds for which no log D values have been reported, such as amino acids, peptides, proteins, nucleosides, and nucleotides, can be estimated using the present method. The wide-ranging log D values (+5.9 to –7.5) of these molecules were estimated for the first time from their log K AN values and the above regression equation. [ABSTRACT FROM AUTHOR]

• alphaLogD is a chromatographic method run on fused core particles. • Application to neutral and basic compounds. • 3 isocratic methods with different contents of organic solvent. • No need for lipophilicity pre-calculation. • Amenable to large range of lipophilicity from −1 to 7. Lipophilicity can be measured with different methods, such as Shake-Flask or liquid chromatography. HPLC presents the advantage of overcoming solubility issues and therefore extending the range of lipophilicity to high values. A specific HPLC method, called ELogD, had been developed 20 years ago on a C 16 -amide stationary phase, enhancing hydrophobic and hydrogen bond interactions to mimic octanol-water partition. The emergence of novel stationary phases and the need for a less complex mobile phase have led to the development of a new HPLC assay called alphaLogD, applicable to neutral and basic compounds at pH 7.4, that combines superficially porous particles with a high number of equilibriums between solutes and stationary phase, leading to a lower number of isocratic methods to determine the logk' w at a higher throughput. Statistical studies have been run to successfully evaluate the alphaLogD method compared to the Shake-Flask method and to allow this lipophilicity measurement into the so-called Beyond-Rule-of-5-molecules space. [ABSTRACT FROM AUTHOR]

Abstract: For the last decade an alkylating agent treosulfan (TREO) has been successfully applied in clinical trials in conditioning prior to hematopoietic stem cell transplantation. Pharmacological activity of the pro-drug depends on its epoxy-transformers, monoepoxide (S,S-EBDM) and diepoxide (S,S-DEB), which are formed in a non-enzymatic consecutive reaction accompanied by a release of methanesulfonic acid. In the present study partition coefficient n-octanol/water (P OW) of TREO as well as its biologically active epoxy-transformers was determined empirically (applying a classical shake-flask method) and in silico for the first time. In vitro the partition was investigated at 37°C in the system composed of the pre-saturated n-octanol and 0.05M acetate buffer pH 4.4 adjusted with sodium and potassium chloride to ionic strength of 0.16M. Concentration of the analytes was quantified by reversed-phase high performance liquid chromatography (RP-HPLC) method in which retention time increased from S,S-DEB to TREO. It was shown that neither association nor dissociation of the tested compounds in the applied phases occurred. Calculated log P OW (TREO: −1.58±0.04, S,S-EBDM: −1.18±0.02, S,S-DEB: −0.40±0.03) indicate the hydrophilic character of the all three entities, corresponding to its pharmacokinetic parameters described in the literature. Experimentally determined log P OW of the compounds were best comparable to the values predicted by algorithm ALOGPs. Interestingly, the P OW values determined in vitro as well as in silico were inversely correlated with the retention times observed in the endcapped RP-HPLC column. It might be explained by the fact that a cleavage of methansulfonic acid from a small molecule of TREO generates significant changes in the molecular structure. Consequently, despite the common chemical origin, TREO, S,S-EBDM and S,S-DEB do not constitute a ‘congeneric’ series of compounds. We concluded that this might occur in other low-weight species, therefore measurement of their P OW by RP-HPLC had to be applied with a special care. [Copyright &y& Elsevier]

Abstract: The solubility vs. pH profiles of five ionizable drugs of different nature (a monoprotic acid, a monoprotic base, a diprotic base and two amphoteric compounds showing a zwitterionic species each one) have been determined through two different methodologies: the classical shake-flask (S-F) and the potentiometric Cheqsol methods using in both instances the appropriate Henderson–Hasselbalch (H–H) or derived relationships. The results obtained independently from both approaches are consistent. A critical revision about the influence of the electrolyte used as buffering agent in the S-F method on the obtained solubility values is also performed. Thus, some deviations of the experimental points with respect the H–H profiles can be attributed to specific interactions between the buffering electrolyte and the drug due to the hydrotrophic character of citric and lactic acids. In other cases, the observed deviations are independent of the buffers used since they are caused by the formation of new species such as drug aggregates (cefadroxil) or the precipitation of a salt from a cationic species of the analyzed compound (quetiapine). [Copyright &y& Elsevier]

The lipophilicity parameters R Mw of twenty-one uridine derivatives were determined by reverse phase thin layer chromatography (RP-TLC). Experiments were performed on RP-18 F254 plates with mixtures of methanol/water as the mobile phases. Amounts of methanol as an organic modifier were in the range 60–85% (v/v) in 5% increments. For nine compounds, logPexp values were determined by shake-flask method. A good correlation was found between logPexp and R Mw (r 0.96). Theoretical logP values for the studied compounds were calculated using nine different algorithms. A correlation matrix was formed to compare the experimental lipophilicity parameters: R Mw , logPexp and theoretical logP values. A good agreement between two experimental methods and theoretical logP values was achieved. The best agreement was obtained between AC/logP vs. logPexp, and R Mw (r 0.98 and 0.96, respectively). [ABSTRACT FROM PUBLISHER]

Abstract: In this paper the pH-equilibrium solubility profiles of six organic drugs are presented. The equilibrium solubility values were determined using the saturation shake-flask and the Chasing Equilibrium Solubility (CheqSol) methods. Results obtained by the two methods are in good agreement. The aim of the present work was to study the validity of the Henderson-Hasselbalch (HH) relationship in the case of structurally diverse weak bases. The significance of pH control and the effect of the salt form (e.g., fumarate) was also investigated. In the case of monoprotic bases, namely papaverine, promethazine, propafenone and ticlopidine the experimental solubility data precisely follow the HH equation until the limit of salt solubility. The common ion effect on salt solubility was found to be significant at low pHs. Deviation from the HH equation in the case of dibasic quetiapine hydrogen fumarate and the ampholyte desvenlafaxine hydrogen fumarate can be easily interpreted with the formation of different salt compositions. It was concluded that precise pH control is essential in shake-flask solubility measurements. It is also critical that the pK a value and the intrinsic solubility are accurately determined when the HH relationship is used to predict the pH-dependent aqueous solubility of drugs. [Copyright &y& Elsevier]

Abstract: The experimental and computational basis of the pH-dependent measurement of solubility of sparingly-soluble ionizable drugs is reviewed. Recently described compound-sparing (but still accurate) approaches, suitable for application in preclinical development, and appropriate for the analysis of solubility of “problematic” molecules, are critically examined. A number of useful experimental methods are reviewed, including the miniaturized shake-flask microtitre plate, the micro solubility self-calibrating direct UV, potentiometric, and the micro dissolution methods. Several molecules were selected as case studies to illustrate important concepts, with re-analysis of literature data using recently established computational tools. [Copyright &y& Elsevier]

It is widely accepted that solubility-pH profiles of ionizable compounds follow the Henderson-Hasselbalch equation. However, several studies point out that compounds often undergo additional processes in saturated solutions, such as sub-micellar oligomerization, micellar aggregation, or drug-buffer complexation among others, which make the experimental profiles deviate from the behavior predicted by the Henderson-Hasselbalch equation. Often, the presence of additional processes is supported by the analysis of experimental data through solubility computer programs. However, the purpose of this work is to experimentally prove the aggregation phenomena for a series of bases for which deviations from the theoretical profile have been observed. To this end, five monoprotic bases (lidocaine, maprotiline, cyproheptadine, bupivacaine, and mifepristone) susceptible to form ionic aggregates in solution have been selected, and mass spectrometry has been the technique of choice to prove the presence of aggregation. High declustering potentials have been applied to prevent aggregates from forming in the ionization source of the mass spectrometer. In addition, haloperidol has been used as a negative control since according to its profile, it is not suspected to form ionic aggregates. In all instances, except for haloperidol, the analysis of the saturated solutions revealed the presence of mixed-charged dimers (aggregates formed by a neutral molecule and a charged one) and even trimers in the case of mifepristone and bupivacaine. For lidocaine, the most soluble of the compounds, the presence of neutral aggregates was also detected. These experiments support the hypothesis that the simple Henderson-Hasselbalch equation may explain the solubility-pH behavior of certain compounds, but it can be somewhat inaccurate in describing the behavior of many other substances.

In the literature the therapeutic nonequivalence of oxytetracycline hydrochloride (OTCH) capsules and tablets was attributed to the different aqueous solubility of polymorphs without their comprehensive study. Our aim was to reveal the effects of polymorphism on equilibrium solubility, dissolution kinetics and the supersaturation of two OTCH polymorphs (stable Form A and metastable Form B).The equilibrium solubility was measured in biorelevant pH range 4–7.4 by the standardized saturation shake-flask method. We also studied the solubility in SGF at pH 1.2 and the effect of the pH change from 1.2 to 5.0 on solubility. The dissolution was studied using real-time concentration monitoring with an ATR probe attached to a UV spectrophotometer (µDISS Profiler). A wide spectrum of solid phase analysis methods (SEM, IR, XRPD, Raman) was applied for characterization of polymorphs and to identify which form is present at the equilibrium solubility. Identical equilibrium solubility values were obtained at the same pHs in region 4.0–7.4 using the two polymorphs as starting materials. The XRPD analysis of the isolated solid phases proved that both polymorphic forms were converted to dihydrate form. In situ monitoring of the dissolution at pH 5.0 showed immediate dissolution, no difference in supersaturation, and short equilibration time for both forms indicating the immediate conversion. In SGF (pH 1.2) Form B dissolved better than Form A and showed significantly different dissolution kinetic and stability. A long-lasting, false chain-citation stating that Form B dissolves 28x better in water than Form A, was cut by the present study (i) revealing that the cited data was measured in IPA not in water, and (ii) proving that only the intrinsic solubility of OTC dihydrate can be measured in water due to conversion of polymorphs under the experimental conditions of solubility measurement. However this conversion is inhibited below pH 1.5, so the differences in solubility and dissolution kinetic found at pH 1.2 may contribute to the interpretation of the different serum-levels reported at solid formulations. Image, graphical abstract [ABSTRACT FROM AUTHOR]