c)To avoid a bottleneck between lead optimization and the entry into human (EIH): F) A fully automated kinetic solubility screen in 384-well plate format using Nephelometry: Laser nephelometry is the measurement of forward scattered light when a laser beam is directed through a solution. com), uSOL Evolution™ (direct UV)(www.pio-inc.com)The µDISS Profiler™ instrument (Pion)( [28], H) Noyes–Whitney template titration method: The process of mass transfer of solute from higher concentration to lower is refered as ... Micronization leads to increase in solubility of drug due to Incresed porosity Incresed surface area Increased angle of repose Increased surface 1. under   pressure, G) Complexation & Coprecipitation: Commercial equipment The solubility of the stable FIII polymorph of the pharmaceutical compound carbamazepine was measured by determining its solubility gravimetrically in ethanol and methanol. Method includes any factors that result in turbidity or light scattering could interfere with data. More specifically, compound solubility can be defined as (11)    Lachman L, Lieberman HA, Kanig JL. b)        Chlormphenicol palmitate suspension the stable α-polymorph produces low serum levels, whereas the metastable β-polymorph yields much higher serum levels when the same dose is administered. Poorly water soluble Figure: 8 Strategies to increase solubility in the physiological pH range by altering physical chemical properties. The TSP can be prepared in bulk D2O facilitating the process. The workflow for the Handling of these solvents in development is usually not yet established and the required cooperation with compound management, informatics specialists, and assay automation specialists is often not in place .New technologies using microfluidic systems could here be beneficial for the distribution of low volumes such as micro droplet devices or the physical contact-free fluid transfer by the acoustic droplet ejection technology. QC Jobs (6)    Indian pharmacopoeia, Govt. In fact, crystals with higher free energy show higher solubility. 5) DIFFERENT TYPES OF SOLUBILITY AND THERE APPLICATION. of the drug by forming metastable crystalline polymorphs of the drug substance which exhibits higher solubility than that of the crystalline drug alone. It is possible for materials to crystallize and in so doing to trap molecules of the solvent within the lattice. c)    Effect of enhanced salt solubility (increased Ksp) on the pH–solubility profile. Because the compounds tested are in dimethyl sulfoxide solutions, the energy required to break the crystal lattice is not factored into the solubility measurements. The system entropy increases slightly because the ordered network of hydrogen bonds among solvent molecules has been disrupted. The Ksp value for a given salt of a compound is a constant value. Jalgaon -425001. The resulting solid comprises charged drug molecules and their associated oppositely charged counterions. (9)    Livery S, Effect of chloride ion on dissolution of different salt forms of haloperidol, a model basic drug. (1)    Lawrence R. A thermodynamic exploration into pharmaceutical drug solubility, D  D T 2001;6: 985 Because so(equilibrium solubility)  and pKa depend on the properties of the drug, not on those of the counterions, this equation can be used to describe the pH at which maximum solubility is achieved. below 2 and/or above 12.Future extensions of both methods regarding   determination of solid state properties seem to be possible. (29)    Li Di, Kerns EH, Biological assay challenges from compound solubility: strategies for bioassay optimization, Drug Discovery Today 2006;11:447-51 Substantial differences of biowaiver dossiers and respective assessments contribute to the impression that a common understanding is lacking on a successful use of the BCS concept to support biowaivers. Solubility: it’s not just for physical chemists  D  D T Nov 2006;11: 1016 Optimizing factors that affect solubility It is well known that amorphous (8) and metastable crystalline (9) forms can convert to forms with higher stability (lower solubility) during dissolution. Procedure For example, Mart´ınez-Oha´rriz et al. Similarly, if the measured solubility falls on the steep portion of the pH–solubility profile, small changes to the pH can have a marked effect on the solubility. Another equilibrium solubility (Thermodynamic solubility), It is true solubility of compound. What is meant by good and poorly soluble depends partly on the expected therapeutic dose and potency. forms can influence the dissolution, bioavailability, stability, and other drug properties. Sometimes it is difficult to There are occasional situations in which the development of a metastable crystalline or amorphous form is justified because a medical benefit is achieved. Job for M.Pharm, MSc as Junior Research Fellow at NIPER, Job for Assistant Professor at Varanasi College of Pharmacy. The concept underlying the Biopharmaceutics Classification System (BCS) finally lead to introducing the possibility of waiving in vivo bioequivalence studies in favour of specific comparative in vitro testing in order to conclude bioequivalence of oral immediate release products with systemic actions. In this case, the higher solubility of the hydrate can be attributed to the stronger hydration of the highly charged zwitterions relative to the uncharged molecule in the anhydrous form. As a result, minimum solubility levels were recommended for candidates, based on their permeability and therapeutic dose, and fundamental properties, such as solubility, were regularly measured. has reported that the resulting crystalline polymorphic form of Diflunisal in its solid dispersions with PEG Pharmaceutical salts pose a special case of apparent solubility that has important implications for drug discovery and development Salts are formed when a compound that is ionized in solution forms a strong ionic interaction with an oppositely charged counterion and maintains that interaction through crystallization. QA Jobs a)    First, simply by increasing the strength of the pKa, the whole pH–solubility curve can be shifted (Figure 4a). Eur J Pharm Sci Dec1999;9(2):171-121 Solvinert filter plates (direct UV) (www.Millipore. lipophilic substructures) can reduce solubility. Since the molecules in crystals with high energy have weaker solid-solid interactions compared to crystals with lower energy, they exhibit higher affinity for the solvent in the surroundings . The results suggest that the system shows a mono-tropic system between 5 °C and 35 °C, while the solubility ratio decreases from 1.20 at 35 °C to 1.12 at 5 °C. Thus, the most stable crystal (lowest energy crystal) form will also have the lowest solubility. c)    Intrinsic solubility means the solubility of the neutral form of an ionizable compound. Following the example of Bogardus and Blackwood , a simple relationship can be developed among pHmax, pKa, intrinsic solubility and salt solubility that can be applied to a specific salt of any monoprotic compound: Ksp, it must be recalled, is related to the constant solubility achieved on the salt plateau and depends on the identity of the salt.     Drug. 2. At the pKa, there are equal concentrations of ionized and unionized forms of the compound in solution. (10)    en.wikipedia.org/wiki/Henderson–Hasselbalch_equation [cited on 2009 Nov 23] Generally, the solubility of metastable polymorphs is kinetically higher than that of a thermodynamically more stable polymorph [33], offering, at least in theory, a solution to bioavailability problems. The ternary phase diagram and solubility measurements only indicated the formation of the 1:1 cocrystal. Zhang et al. Nearly all pharmaceutical drug products are required to be in a molecular dispersed form (solvated) before adsorption across biological membranes can occur. Figure: 5. 4) PROBLEMS THAT OCCUR WHILE DETERMINING SOLUBILITY: Thermodynamic equilibrium will always seek the overall lowest energy state (most stable) of the system; thus, only the ‘real’ equilibrium solubility reflects the balance of forces between the solution and the most stable, lowest energy crystalline form (most stable) of the solid. [17] Figure: 5. Although this is an attractive possibility, it can be difficult to achieve because the factors governing intrinsic solubility (e.g. Therefore, the development of models to predict the aqueous solubility of drug candidates from their chemical structure has attracted considerable attention. Equation (4.2) shows an increase of solubility as the melting point decreases. www.crcom.se APER pH-Solubility diagrams and their usefulness in characterization of salts of poorly soluble drug substances For weak acids or bases, the aqueous solubility of a salt of the ionized form is often much higher than that of the free (acid or base) form. Maharashtra, India. Thus, cocrystals could offer a superior strategy to improve the solubility of BCS class IV drug compared to metastable polymorphs and amorphous dispersions of furosemide. 3. Predictive models based on molecular descriptors also help understanding what feature(s) limits solubility and can thus provide useful information to medicinal chemists. E.g. Amorphous state of the drug has a greater solubility than the crystalline form but the amorphous form is less stable and degrades quickly in presence of humidity and temperature. 6) PARAMETER TO BE CONSIDERED WHILE MEASURING SOLUBILITY: A)  pH of solution Three milliliters of the appropriate formulation vehicle is then added and vortex the sample. ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. (26)    Melissa L, Tesconib M, Tischlera M. Use of 1H NMR to facilitate solubility measurement for drug discovery compounds. This can be explained by the change in solid state of the drug during the electrospraying process, as the drug in amorphous state exhibit higher metastable solubility than its crystalline form. Above parameter should be considered while determining solubility. This method is used for the determination of solubility of in drug in polymer matrix. Similarly, excess counterions can drive the drug out of solution through the common ion effect. In the absence of intermolecular interactions (gas phase), the solubility reflects only the interaction between solute and solvent, shown as Sg. Rapid data visualization will help to uncover intimately linked compound and solvent properties that positively or negatively affect each other and may thus facilitate and speed up decision making in drug discovery and development; examples are the recently reported “self-organized” solubility-and PAMPA excipient plots, the plotting of solubility profiles as a function of substituent’s , the bioavailability score, solubility-pH plots for forced degradation studies  or the solvent miscibility plots . The method was based on the simple principle that the fraction of drug solubilised within the matrix does not contribute to the melting endotherm associated with the dispersed drug fraction. Solubility determination can be done by ultraviolet absorption, nephlometry, Nuclear magnetic resonance and Potentiometric in drug discovery. TSP has a single proton signal that is isolated from the signals of the formulation excipients and the compounds of interest, and therefore, eliminates the potential for interference with peaks resulting from the compound of interest. The relationship between the molar solubility of a drug in water, S w, at a temperature T (in kelvins), and the melting point T m, for a non-ideal solution may be written as where is the entropy of fusion (melting), γ is the activity coefficient and is the molar volume of the solvent. A drug is considered highly soluble if its highest dose strength is soluble in less than 250 mL of water, as tested over a pH range of 1–7.5. Deionized water of resistivity >1014O cm is used throughout the experiment. This is not the case with NMR. Precipitate formed in this pH range can be in either the free form or the salt form, depending on the strength of the solid state interactions. The time needed to reach equilibrium solubility was determined by analyzing samples of the equilibrating solution at different time points to establish constant drug solubility. Faculty Jobs NMR solubility analysis is the relatively lower sensitivity compared with UV detection and mass spectrometry techniques, which limits analysis of samples having low solute concentrations. There is still a risk that this foreshortened incubation will not be sufficient for metastable crystal forms to convert to the most stable form, and that the measured concentration will represent the apparent (intrinsic) solubility of a different crystal form. It is clear from the above equations that pH has an enormous effect on the solubility of ionizable compounds. [11], Figure: 3         PH–solubility profile for a compound with a single, basic pKa value of 5. In time, a second equilibrium is established between the drug in solution and a second polymorph. The solubility of all drug substances is normally determined during the preformulation stage, and it is crucial to know whether the determined values represent genuine equilibrium solubilities (i.e., thermodynamic values) or whether they represent the values associated with a metastable condition (i.e., kinetic values). The NMR method is fast, and sample preparation is simple if the formulation materials are made ahead of time in larger batches. Before each experiment, accurate pKa values were measured at 25°C and at 37°C on the Sirius GLpKa titrator. However, this approach is expensive and without guarantee of success. Example,  solubility of metroindazole in silicon matrix is determined by the HDSC is .0216%w/w at 4000c/min. Take 1 gm of solute dissolve in the solvent of choice in a beaker .stir the solution for specific period of time & allow the solution to reach equilibrium carry out the analysis of the final solution after equilibrium is achieved  & find out the concentration of solution . Low aqueous solubility is the major problem encountered with formulation development of new chemical entities as well as for the generic development. The solubility of all drug substances is normally determined during the preformulation stage, and it is crucial to know whether the determined values represent genuine equilibrium solubilities (i.e., thermodynamic values) or whether they represent the values associated with a metastable condition (i.e., kinetic values). A schematic titration head is shown in Figure 7. Allotropy refers to polymorphism for chemical elements.Polymorphism is of practical relevance to pharmaceuticals, agrochemicals, pigments, dyestuffs, foods, and explosives. Nonetheless, raising Ksp is perhaps the most valuable scheme for enhancing the solubility of pharmaceutical molecules because, unlike changes in So or pKa, it does not require alterations to molecular structure that could adversely affect pharmaceutical activity. Application: Use: Finally, drug dissolution, will also be a topic for solubility assays in the future. All titrations were performed in 0.15 M KCl solution, to mimic the ionic strength of the blood, under argon atmosphere and with degassed reagents. This risk must be taken into consideration when running a solubility experiment with material that is not known to be the most stable crystalline form. b)    Increases in the intrinsic solubility of the unionized molecule might lead to increases in solubility across the whole pH–solubility profile (Figure 4b). • Increasingly more drugs with poor solubility being made. It is commercially used for treatment of onychomychosis. B) High speed DSC (hyper-DSC) tool to measure the solubility of a drug within a solid or semi-solid matrix. According to Equation 20.1 , an increase in the total surface area of drug in contact with the gastrointestinal fluids will cause an increase in dissolution rate. If a compound with the same potency has a solubility of less than 0.01g/L it can be considered poorly soluble. The success of a drug as a candidate for development to the market place depends on issues such as stability and bioavailability. As the counterion concentration in solution increases, the dissolved drug concentration decreases to maintain the Ksp. 1996;1:7 solubility advantage also raises the risk of a solid-state transformation.