Exploring Differnet Polymorphic Forms Biology Essay

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Tejal Prajapati et.al., (2010) 23 Studied on crystal forms of carbamazepine in various solvents on crystalline modifications and the solubility and dissolution of carbamazepine immediate release tablet by in vitro dissolution studies. Solubility enhancement was carried out by using different types solvents like ethanol, acetone and chloroform. The physical state of the prepared crystal forms and pure drug was determined by SEM, DSC, PXRD and FTIR. Crystals prepared with ethanol at room temperature shows highest solubility and better drug release profile than other forms.

Nokhodchi et.al., (2010) 24 prepared ibuprofen crystals by using solvent change crystallization technique. Ibuprofen was dissolved in ethanol and crystallized with water in the absence or presence of different types of hydrophilic additives (PEG 6000, 8000, Brij 98P and PVA 22000) using with different concentrations. Ibuprofen crystals physico-mechanical properties were studied by flow property , density, tensile strength and dissolution behaviour, SEM, DSC and FT-IR. Ibuprofen samples crystallized with presence of PEG 6000 and 8000 and PVA showed reliable increase in the tensile strengths of the directly compressed tablets, and some other additives like Brij 98P did not produced any improvement in prepared ibuprofen crystals.

Talluri chandrashekar et.al., (2010) 25 Developed four different types of polymorphs (Form I, Form II, Form III and Form IV) of Chlorzoxazone with different solvents. The obtained polymorphs were characterized by using Optical Microscopy, DSC, XRD and IR spectroscopic methods. This characterization study proved that the Form I, Form II shown higher solubility profile than crystal forms of Form III, Form IV and pure Chlorzoxazone.

Rajesh A. Keraliya et.al., (2010) 26 Investigated 14 pure good solvents were selected for the crystallization of tolbutamide. Crystals were obtained in only 10 out of the 14 solvents. Prepared Crystals were characterize by differential scanning calorimetry, optical microscopy, and in vitro dissolution. All types crystals were determined as isomorphic by differential scanning calorimetry. Dissolution rate was efeected by Crystal forms of tolbutamide

Cheng-Hung Hsu et.al., (2010) 27 Studied the processes of polymorphic forms transformation in different gabapentin polymorphs. Four polymorphs of GBP were prepared and then characterized by differential scanning calorimetry, thermogravimetric analysis, FTIR microspectroscopy and X-ray powder diffractometry. A one-step novel hot-stage FTIR microspectroscopy was successfully applied to simultaneously and continuously investigate to the progressive processes of polymorphic forms transformation of prepared crystals and steps of thermal-induced polymorphic interconversion of gabapentin polymorph in the solid state.

Gen Hasegawa et.al., (2009) 28 Examined the thermodynamic stability of prepared tolbutamide polymorphs by using calorimetry and spectroscopic analysis. The heat of solution (∆H) of Forms I-III measurements were carried out in solent of dimethylsulfoxide between 298.2K and 319.2 K. Solubility data observed and confirmed the change in ∆H of Form I around 308.2 K. XRD, DSC measurements of Form I characterized a polymorphic transformation occurred (Form IL→unknown form) at 311K. The crystal structure of the Form IH was determined by PXRD pattern, and the change in the solid-state NMR spectrum confirmed the transformation occurred in the crystal structure of tolbutamide Form IL.

Roya Talari et.al., (2009) 29 Investigated Gliclazide was recrystallized with 12 different stabilizers and the effects of each stabilizer on micromeritic behaviors, morphology of microcrystals, dissolution rate and solid state of recrystallized glicazide were studied. Recrystallized samples shown faster dissolution rate than pure drug of gliclazide and the fastest dissolution rate was observed the samples recrystallized with PEG 1500. In situ micronization of pure gliclazide by pH change method may successfully be used to produce micron-sized drug particles. The pure drug of gliclazide is rod or rectangular shape, whereas the obtained crystals produced in presence of stabilizers, depending on the type of stabilizer, were very fine particles with irregular, cubic, rectangular, granular and spherical/modular shape. The results shown that crystallization of gliclazide forms with stabilizers reduced the crystallinity of the samples confirmed by XRPD and DSC. In situ micronization of gliclazide by pH change method can successfully used to produce micron-sized drug particles to improve dissolution rate.

Renu Chadha et.al., (2009) 30 Characterized different prepared forms of methotrexate, five different forms were obtained. Observed of a desolvation endotherm in the DSC accompanied by mass losses in TGA for forms I, II, IV and V and shown these forms are acetonitrile solvate hydrate (form I), trihydrate (forms II and IV) and dimethylformamide solvate (form V), respectively. The desolvation peak was absent in form III (obtained from methanol) indicating the absence of any solvent of crystallization. This form was found partially crystalline by its XRPD pattern. Solution calorimetry was further used to differentiate the forms as they differ in lattice energy, resulting in different enthalpies of solution. The dissolution and solubility rate profiles were correlated to the enthalpy of solution and subsequently with crystallinity of all the forms; and form III having the highest dissolution rate.

Mange Ram Yadav et.al., (2008) 31 developed five different crystal forms of pefloxacin using solvents of varying polarity, observed the dissolution kinetics of five different polymorphs of pefloxacin. The polymorphs differed in their dissolution profile and all of them shown unusual behavior of highest dissolution at end of 15 min than some what similar. The rate of dissolution decreasing and got constant dissolution release values after 4 hrs.

Shan-Yang Lin et.al., (2007) 5 Investigated the famotidine polymorph of two forms A & B. It describes the grinding or compression process may produce the polymorphic transition of famotidine in ground mixtures or compressed compacts in tabletting time. The synergistic effect of temperature on the grinding or compression process was also investigated. The polymorphic transition of famotidine in the ground mixtures was determined by confocal Raman microspectroscopy, differential scanning calorimetry. Mechanical forces, such as grinding and compression are having significant effect on the Famotidine polymorphic transformation.

Ilma Nugrahani et.al., (2007) 32 To evaluate the solid state interaction between amoxicillin trihydrate and potassium clavulanate. The interaction was observed by using DSC, XRPD, FTIR and SEM. compositon of amoxicillin trihydrate and potassium clavulanate were prepared in ten molar ratios and analyzed by DSC to obtain the thermal profile and a phase diagram. From this phase diagram, the molar ratio point of interaction was determined. Thermo profile obtained by DSC analysis of the binary systems showed that endothermic curves of molar fractions of 1:9-5:5 overlapped at 201°C. FTIR spectrum of binary system in the molar ratio of 5:5 showed the loss of hydrate spectra from amoxicillin trihydrate. We conclude that the interaction was involved strong hydrogen bonding between hydrates of amoxicillin and potassium clavulanate which produced a co-crystal system like a solid dispersion.

Cristina Puigjaner et.al., (2007) 33 developed new polymorphic forms of Norfloxacin A, B & C. These characterized by a variety of methods including powder X-ray diffraction, vibrational spectroscopy (IR and Raman), thermal analysis (DSC and TG), SEM and solid-state NMR spectroscopy. The relationship between the new form C and the previously known forms A and B have been studied. Moreover, the crystal structure of the known form A has been solved by single-crystal methods.

C.G. Kontoyannis et.al., (2007) 34 reported polymorphic forms of Risperidone in film coated commercial tablets was attempted by using IR spectroscopy, Raman spectroscopy and X-ray powder diffraction. The stability of this polymorph through time and during the manufacturing process was also examined. The inability of IR and Raman techniques to identify the presence of polymorph A in the tablets, Polymorph A was proved to be stable during the manufacturing process time and after the storage period of 2 years.

Wang Jingkang et.al., (2007) 35 reported the effects of solvent and impurity on the crystal habit of 11α-hydroxy-16α, 17α-epoxyprogesterone (HEP) grown from solution were studied by using SEM. Long prismatic crystals were obtained when HEP was crystallized in pure acetone and N, N-dimethylformamide, while blocky crystals were obtained in pure chloroform by cooling crystallization method. One kind of isomorphic impurity, 16α, 17α-epoxyprogesterone (EP) was selected to examine its effect on the HEP crystal habit. The habit of produced HEP crystals was greatly modified from prismatic to octahedral shape. The DSC and X-ray powder diffraction analyses showed that the change of crystal habit was originated from the crystal structure modification.

Piera Di Martino et.al., (2007) 36 reported crystal forms of nimesulide obtained by crystallizing from an ethanol solution, different from the pure drug nimesulide reference sample, it was confirmed by XRPD, DSC and solid cross polarization-magic angle spinning (13C-CPMAS) NMR. When crystallized from dioxane nimesulide forms are solvate. In addition to the physico-chemical characterization, the technological properties of nimesulide. The form obtained by desolvation of dioxane solvate given positive effect on tableting properties, increasing both compressibility and tabletability of nimesulide forms.

Joao Canotilho et.al., (2007) 37 performed crystalline forms of atenolol, from evaporation of an ethanol/water solution. (R, S)-Atenolol crystallizes in the centrosymmetric space group C2/c, and S-atenolol crystallizes in a noncentrosymmetric space group C2. One symmetry independent molecule in (R, S)-atenolol crystals and two symmetry independent molecules in S-atenolol. However, two different molecular conformations were identified in the (R, S)-atenolol and three different conformations were isolated in S-atenolol. Flexibility of molecular segments of the carbon chain was seen in conformational isomorphism and in the atomic positions uncertainty. The molecular conformations given by X-ray diffraction were fully relaxed at the HF/6-31G* level of theory. The optimized structure was used as reference in comparison with molecular conformation in the solid state.

Reddy et.al., (2005) 38 investigated a novel crystalline form of cetirizine monohydrochloride. The crystalline forms of cetirizine monohydrochloride has an x-ray diffraction pattern, differential scanning calorimetry.

Kati Pollanen et.al., (2005) 39 investigated polymorphic of sulfathiazole, this diffuse reflectance Fourier transform infrared spectroscopy together with multivariate statistical process control analysis, soft independent modeling of class analogy, orthogonal signal correction preprocessing and partial least squares regression methods were applied to polymorphic characterization of crystalline bulk product. X-ray powder diffraction was used as a reference technique.

Ali Arslantas et.al., (2005) 40 polymorphs of L-ascorbic acid considered eight space groups and assuming one molecule in the asymmetric unit. A number of possible crystal structures were found, including the experimental structure also. The experimental structure has low lattice energy. The number of hypothetical crystal structures was reduced considerably by removing space-group symmetry constraints, or by a primitive molecular dynamic shake-up. Sufficient structures of equal or lower energy compared with the experimental structure remained to suggest that other factors need to be considered for polymorph predictions of materials.

Schmidt et.al., (2005) 41 reported Benzocaine (BZC), butambene (BTN) and isobutambene (BTI) are basic local anaesthetic agents of the ester type, exist in two polymorphic crystal forms and their solid state characterized by thermomicroscopy, DSC, FTIR, FT-Raman-spectroscopy and XRPD. The endothermic transformation of mod. I0 is thermodynamically stable at ambient conditions (heat of transition rule) whereas mod. II is enantiotropically related to mod.I0 is metastable at temperatures. The metastable forms show different kinetic stabilities at room temperature.

Vijayavitthal T Mathad et.al., (2005) 42 investigated six polymorphs of donepezil hydro bromide in various solvents, physical properties have been identified and characterized by PXRD, DSC, TGA, IR spectroscopy and Karl Fischer techniques. Different methods used for the synthesis of each polymorph and characterization of these novel polymorphs.

Arvind k. Bansal et.al., (2004) 43 studied polymorphic form of clopidogrel bisulphate form I and form II a selective and irreversible inhibitor of ADP-induced platelet aggregation. Thermal (DSC, TGA, HSM), crystallographic (XRD) and spectroscopic (FTIR) methods were used for characterization of these forms. After characterization of active pharmaceutical ingredient, these techniques were further used for identification of the polymorphic form present in three marketed formulations (tablets). FTIR method was successfully developed and validated for the quantification of form I in polymorph mixtures.

David J. W. Grant et.al., (2004) 44 reported polymorphic form of s Piroxicam in two forms. The difference in energy of the two polymorphs, I and II, of Piroxicam arises predominantly from the difference between their lattice energies, rather than between their conformational energies. Despite stabilization of the polymorphs by hydrogen bonds, a loss of polymorphic memory was observed upon cryogrinding the two polymorphs, leading to differences in recrystallization behavior between amorphous Piroxicam prepared from polymorphs I and II.di

Young-Taek Sohn and Hyun Ok Seo et.al., (2004) 45 reported four crystal forms of ketorolac have been obtained by recrystallization in organic solvents under variable conditions. Different ketorolac polymorphs and pseudopolymorph were characterized by XRPD, DSC, and thermogravimetric analysis. The dissolution studies in water at 37±0.5oC, four crystal forms showed different patterns. The solubility of Form I were the highest. Form I and Form III were shown to have a good physical stability at room temperature for 60 days. Form II is converted to Form III and Form IV is converted to Form I after 60 days storage. Indicate that crystalline polymorphism for ketorolac is readily inter-convertible and the relationship may take into formulation of the drug.

Sari Airaksinen et.al., (2004) 46 investigated polymorphism of theophylline monohydrate, two polymorphic forms. During drying phase of wet granulation, theophylline monohydrate transforms either stable (form I), or metastable (form Iâˆ-) form of anhydrous theophylline. The effect of two drying methods multichamber microscale fluid bed dryer or variable temperature X-ray powder diffractometer on the relative amounts of the different theophylline forms remaining in the dried granules were analyzed using XRPD and near-infrared spectroscopy. Form Iâˆ- theophylline after drying at 40-50 â-¦C with both drying techniques. Additional drying methods, including, can be possible polymorphic transformations and mechanisms, such as triboelectrification or recrystallization, in drug ingredients during the manufacturing process.nd

Mahua Sarkar et.al., (2008) 47 this investigation is to characterize nevirapine from commercial samples and samples crystallized from different solvents under various conditions. The solid-state behavior of nevirapine samples was investigated using a variety of complementary techniques such as microscopy (optical, polarized, hot stage microscopy), differential scanning calorimeter, thermogravimetric analysis, Fourier transform infrared spectroscopy and powder X-ray diffractometry. The samples recrystallized from different solvent systems with varying polarity yielded different crystal habits. The intrinsic dissolution rate of recrystallized samples was lower than the commercial sample. Amorphous form showed slightly higher aqueous solubility than the commercial crystalline form.

Makoto Otsuka & Fumie kato et.al., (2003) 48 develop a rapid chemometrical method based on near-infrared spectroscopy to determine indomethacin polymorphic content in mixed pharmaceutical powder and tablets. Mixed powder samples with known polymorphic contents of forms α and γ were obtained from physical mixing of 50% of IMC standard polymorphic sample and 50% of excipient mixed powder sample consisting of lactose, corn starch, and hydroxypropyl-cellulose. X-ray powder diffraction profiles and NIR spectra were recorded for 6 kinds of standard materials with various polymorphic contents. NIR spectroscopy provides a more accurate quantitative analysis of polymorphic content in pharmaceutical mixed powder and tablets than does conventional x-ray powder diffractometry.

Sabiruddin Mirza et.al., (2003) 49 investigated erythromycin crystal forms with organic solvents, (acetone, methylethylketone, ethanol, and isopropanol) both in the presence and in the absence of water on the crystallization behavior of erythromycin. It was established that pure organic solvent, or 1:9 or 1:1 water-organic solvent mixtures, the solvate is always crystallized. However, the recrystallization of erythromycin from 2:1 water-organic solvent (excluding methylethylketone) mixture results in the formation of a crystal hydrate form. Thermo-gravimetric analysis showed that the loss of volatiles by all of the solvated crystals is nonstoichiometric. The desolvation behavior of the solvates with the organic solvents studied by variable-temperature x-ray powder diffraction indicates that in contrast to erythromycin dihydrate, they belong to a different class of solvates those that produce an amorphous material upon desolvation.

R. Fausto et.al., (2003) 50 investigated 3-Amino-1-propanol (3AP) by differential scanning calorimetry, and low temperature powder X-ray diffraction and Raman spectroscopy. Fast cooling rates produce an amorphous state that, on heating, crystallizes into the metastable polymorph. At higher temperatures, this metastable crystalline phase converts into the stable crystal. Using intermediate cooling rates, 3AP crystallizes as the metastable polymorph, the solid l solid transition leading to conversion of this form into the stable polymorph occurring during the subsequent heating. Slower cooling rates enable formation of the stable crystal on cooling. The two crystalline polymorphs were structurally characterized by powder X-ray diffraction and Raman spectroscopy. It was concluded that different conformations are assumed by the individual molecules of 3AP in the two crystalline varieties, with the molecules assuming the all-trans configuration in the metastable crystalline state and having the heavy atom backbone trans but the NH2 and OH groups gauche in the stable crystal.

Amy J. Harshaw et.al.,(2003) 51 examined polymorphism of sulfathiazole in four polymorphic crystalline forms exist in solvent used n-propanol, acetone/chloroform, water, characterized by differential thermal calorimetry and solubility studies in four different solvents and recrystallizing it under different conditions as a function of temperature.

Adam J. Matzger et.al., (2002) 52 determined the crystal structure of a new polymorph of nabumetone that displays dramatically lower stability yet differs only in weak intermolecular interactions from the known form.

Judith Maria Rollinger et.al., (2002) 53 investigated three crystal forms of torasemide from various organic solvents. Physicochemical properties were determined by thermoanalysis (hot-stage microscopy, differential scanning calorimetry, thermogravimetry), Fourier transform infra-red and Raman spectroscopy, and X-ray powder diffractometry. The hygroscopicity, relative stability, true density, and heat of solutions were determined. The dissolution behaviour of mod. I and II was investigated as a function of pH, temperature, and in addition to surfactants. Mod. II is nearly three times more soluble than mod. I (mod. I, 0.34 mmol l21; mod. II, 0.93 mmol l21 at 208C, pH 4.90) and proved to be highly kinetically stable. The present results physicochemical characterization of the crystal forms of torasemide.

S. Agatonovic-Kustrin et.al., (2001) 54 determined of polymorphic forms of ranitidine HCl in two forms 1 and 2. To analyze polymorphic purity of crystalline ranitidine HCl by solid-state techniques, diffuse reflectance infrared Fourier transform spectroscopy and X-ray powder diffractometry were combined. The results demonstrate that DRIFTS combined with XRPD may be successfully used to distinguish between the ranitidine HCl polymorphs and to quantify the composition of binary mixtures of the two.

A.R. Rajabi-Siahboomi et.al., (2001) 55 investigated crystal form of Ibuprofen from methanol, ethanol, isopropanol, and hexane. The samples crystallized from methanol and ethanol had a polyhedral crystal habit, while hexane was needlelike, isopropanol were elongated crystals. XPD and DSC studies that these samples were structurally similar; The results showed that crystal habit modification had a great influence on the mechanical properties (compressibility, flow rate, and bulk density) of ibuprofen crystals. Samples obtained from methanol and ethanol exhibited the highest bulk density and the best flow rate, while those from hexane showed the lowest bulk density and the worst flow rate. The samples obtained from ethanol exhibited the best compression force/hardness profiles, and those obtained from hexane produced the softest tablets.

John Bauer et.al., (2001) 56 investigated Ritonavir polymorphism using solid state spectroscopy and microscopy techniques including solid state NMR, Near Infrared Spectroscopy, powder X-ray Diffraction and Single crystal X-ray. An unusual conformation was found for form II that results in a strong hydrogen bonding network. A possible mechanism for heterogeneous nucleation of form II was investigated. Ritonavir was found to exhibit conformational polymorphism with two unique crystal lattices having significantly different solubility properties. Although the polymorph (form II) corresponding to the "cis" conformation is a more stable packing arrangement, nucleation, even in the presence of form II seeds, is energetically unfavored except in highly supersaturated solutions. The coincidence of a highly supersaturated solution and a probable heterogeneous nucleation by a degradation product resulted in the sudden appearance of the more stable form II polymorph.

Changquan Sun and David J. W. Grant et.al., (2001) 57 developed bulk powders of sulfamerazine polymorph I and of two batches, II(A) and II(B) of different particle size, of polymorph II were crystallized. The powders were compressed to form tablets whose porosity and tensile strength were measured. The relationships between tensile strength, porosity and compaction pressure were analyzed. The sensitivity of tensile strength to compaction pressure, known as the tabletability, follows the order, I >> II(A) > II(B) and the porosity at the same compaction pressure, which measures the compressibility, follows the order, I << II(A) < II(B). Therefore, the superior tabletability of I over II(A) or II(B) is attributed to its greater compressibility. Molecular simulation reveals slip planes in crystals of I but not in II. Slip planes provide I crystals greater plasticity and therefore greater compressibility and tabletability. Larger crystal size of II(B) than of II(A) leads to fewer contact points between crystals in the tablets and results in a slightly lower tabletability. Slip planes confer greater plasticity to crystals of I than II and therefore greater tabletability.

Malamataris et.al., (2000) 58 investigated a crystalline form of glibenclamide, with higher melting point (218°C) and lower solubility in simulated gastric and intestinal fluids, was to elucidate transitional phases by melting, cooling and reheating. The new form was obtained from the glassy state, by applying sublimation at 130-160°C. It was characterised by differential scanning calorimetry, infrared spectroscopy, scanning electron microscopy, hot-stage microscopy, X-ray powder diffraction and solubility studies.

Yumiko Kobayashi et.al., (2000) 59 investigated carbamazepine (CZP) polymorphs and pseudopolymorphs (form I, form III and dihydrate) dissolution behaviors, & bioavailabilities. The solubilities of both anhydrates (form I and form III), calculated from the initial dissolution rate of each anhydrate, were 1.5-1.6 times that of the dihydrate. The inconsistency between the order of initial dissolution rates and that of AUC values at the high dose may have been due to rapid transformation from form III to dihydrate in GI fluids.

Gamberini et.al., (2000) 60 developed three different polymorphic forms of carbamazepine. Differences due to polymorphism and pseudopolymorphism can affect bioavailability and effective clinical use. To characterise by FT-IR spectroscopy, XRPD, DSC, Hot Stage FT-IR thermomicroscopy. The existence of three different polymorphic forms for anhydrous carbamazepine: Form III, the commercial one, Form I, obtained by heating Form III and Form II, crystallised from ethanolic solution. Hot Stage FT-IR thermomicroscopy proved its analytical potential to characterise the drug's polymorphism.

Young-Taek Sohn et.al., (2000) 61 investigated recognized that physicochemical properties of drugs are affected by the type of polymorphic crystalline form of drugs. Clarithromycin three polymorphic crystalline forms. New method involved simple recrystallization of clarithromycin in solvents like hexane, heptane or ethers, isopropyl ether. DSC, XRPD, used to compare the crystalline form of resultant powder with form II crystal prepared by conventional method. It indicated that improvement in purity of the form II crystal for clarithromycin as well as a significant cost reduction by novel method.

Robert E. Dinnebier et.al., (2000) 62 Studied three crystalline modifications (A, B, and C) of telmisartan and their crystal structures have been determined by single-crystal X-ray diffraction (pseudopolymorph C) and the method of simulated annealing from high-resolution X-ray powder diffraction data, IR. For the structure solutions of polymorphs A and B, 13 degrees of freedom (3 translational, 3 orientational, 7 torsion angles) were determined in ~2 h of computer time, demonstrating that the crystal packing and the molecular conformation of medium-sized (MW » 500) pharmaceutical compounds can now be solved quickly and routinely from high-resolution X-ray powder diffraction data

Martınez-Oharriz et.al., (1999) 63 to investigate the physico-chemical characteristics of diflunisal-PEG 4000 solid dispersions prepared by melting, solvent and melting-solvent methods. Solvents are chloroform, methanol and ethanol-water the drug present in different polymorphic forms. The characterization of solid dispersions was performed by X-ray powder diffraction of the diflunisal-PEG systems. In solid systems obtained by the solvent and melting solvent methods the drug solidifies in form III in ethanol / water and methanol, while polymorph IV crystallizes in chloroform. Finally, DSC thermograms and hot-stage microscopy data of solid dispersions prepared by the melting method have allowed to draw the diflunisal-PEG 4000 solid-liquid phase diagram.

Shivakumar et.al., (1999) 64 studied the effect of solvents on the crystallization of paracetamol crystals were characterized by FT-IR, DSC and Powder XRD patterns. The results indicate that crystals obtained from different solvents exhibited different physicochemical properties. The crystals of desired physicochemical properties may be obtained by selecting solvents of different solubility parameter and dielectric constants.

Y.E. Hammouda et.al., (1999) 65 reported sulphadiazine (SD) a suspension of the drug in a preselected solvent (5% aqueous ammonia solution) was stirred under controlled conditions. The solvent was subsequently removed and the material dried. The effect of experimental variables such as stirring speed and time, powder/ solvent ratio and inclusion of additives (Tween 80, sodium chloride and PVP) on the properties of solvent treated SD was assessed. Data obtained were compared with those for SD recrystallized under identical conditions. Solvent treatment of SD in the absence of additives resulted in a limited change in crystal morphology as indicated by SEM. This was associated with improved flowability and a limited reduction in dissolution rate relative to untreated SD. On the other hand, recrystallized SD exhibited superior flowability but a considerably low dissolution rate. Solvent treatment of SD in the presence of 2% PVP produced a microgranular directly compressible material.

Monica Bartolomei et.al., (1999) 66 investigated the crystallization conditions and the physicochemical properties of the modifications I and II of propranolol HCl, two forms were described. FTIR spectroscopy, PXRD, thermal analysis, solubility and dissolution studies were used for characterization. Their stability was followed at room temperature over a period of 1 year and under different conditions of temperature, grinding and compression to verify the tendency to solid-solid transition and to study the existence range of the two forms. The equilibrium solubilities of the two polymorphs in n-octanol were determined as well as their dissolution profiles as pellets in aqueous medium. These studies showed that form I, the less thermodynamically stable, was more soluble (by more than 34%) and dissolved faster than form II in agreement with the thermodynamic rules.

Peter York et.al., (1998) 67 reported Polymorphic forms of Chlordiazepoxide in five forms, was characterized and distinguished from the standard form (form I) by X-ray diffractometry, differential scanning calorimetry, infrared spectroscopy, microscopy, solution calorimetry, and solid-state nuclear magnetic resonance. Recrystallization from other alcoholic solutions (ethanol, propanol, and butanol) and toluene yielded form I. Visual examination by hot stage microscopy in this temperature range revealed a dramatic solid-state transition. When compared with the published crystal structure of form I, the cell symmetry, volume, and density were similar. Both structures consisted of four crystallographically independent molecules linked in pairs through intermolecular hydrogen bonding. Differences were observed in the packing arrangement of the dimers in the polymorphs. The small heat of transition calculated from solution calorimetry (1.5 kJ mol-1) was sufficient to effect a crystallographic rearrangement of the dimers.

Carolina B. Romanuk et.al., 68 reported polymorphism in a new ciprofloxacin saccharinate in two polymorphic forms. To characterize and distinguish both polymorphic forms we used solid state techniques: powder X-ray diffraction, single crystal X-ray diffraction, Infrared and Solid State NMR.

Ricardo Alves et.al., (2010) 69 The thermal behavior of two polymorphic forms of rifampicin was studied by DSC and TG/DTG. The thermoanalytical results clearly showed the differences between the two crystalline forms. Polymorph I was the most thermally stable form, the DSC curve showed no fusion for this species and the thermal decomposition process occurred around 245 °C. The DSC curve of polymorph II showed two consecutive events, an endothermic event (Tpeak = 193.9 °C) and one exothermic event (Tpeak = 209.4 °C), due to a melting process followed by recrystallization, which was attributed to the conversion of form II to form I. Isothermal and non-isothermal thermogravimetric methods were used to determine the kinetic parameters of the thermal decomposition process. Yielding values for polymorph form I and II of 154 and 123 kJ mol-1, respectively. The mean values found for form I and form II were 137 and 144 kJ mol-1, respectively.

Masato OHTA et.al., (1999) 70 The heat of crystallization and heat of solution of cefditoren pivoxil of different crystallinities were determined by differential scanning calorimetry and isothermal microcalorimetry, respectively. The heat of crystallization and heat of solution of ground cefditoren pivoxil showed good linear correlation with the degree of crystallinity determined by Ruland's method by powder X-ray diffractogram. The changes in crystallinity of amorphous cefditoren pivoxil by adsorption of alcohol vapor could be evaluated for small amounts of sample by use of heat of crystallization. Since the apparent dissolution rate of cefditoren pivoxil of various crystallinities correlated with the heat of solution, microcalorimetry was found to be useful for prediction of dissolution behavior.

Arvind K. BANSAL et.al., (2009) 71 amorphous systems have attracted considerable attention due to their favorable properties; however, their stability issues still pose a major challenge. The purpose of the present work was to investigate the role of molecular mobility and moisture in the physical stability of a selected pharmaceutical amorphous system. Irbesartan, a relatively stable glass, was chosen as the model drug, as it exhibits a good physical stability (resistance to crystallization) at temperatures below the glass transition (Tg-50 K). The amorphous system was annealed at temperatures 298 K (25 °C) and 313 K (40 °C) at 0 and 75 % RH to study the effect of temperature and moisture on its relaxation behavior. Differential scanning calorimetry (DSC) was used to characterize both the crystalline and the freshly prepared glass, and to monitor the extent of relaxation at temperatures below glass transition (Tg) as well as heat capacity changes as a function of temperature. Molecular relaxation time constant (τ) decreased drastically from 302 years to 68 hours with the increase in annealing temperature as determined by Kohlrausch-William-Watts (KWW) equation. Irbesartan was found to be 'relatively' stable in the amorphous state and presented a challenge for temporal measurements. Hence, at low annealing temperatures, (Tg-50 K or below) initial relaxation time (τ0) was estimated using the calorimetric based approach. Amorphous Irbesartan was non-hygroscopic and retained its glassy nature under the accelerated stability conditions.

Robert E. Dinnebier et.al., (2000) 72 Three crystalline modifications (A, B, and C) of telmisartan have been detected and their crystal structures have been determined by single-crystal X-ray diffraction (pseudopolymorphs C) and the method of simulated annealing from high-resolution X-ray powder diffraction data (polymorphs A and B). The compound is of interest because of its use as an angiotensin II receptor antagonist. Polymorph A crystallizes in space group, Polymorph B crystallizes in space group as structure solutions of polymorphs A and B, 13 degrees of freedom (3 translational, 3 orientational, 7 torsion angles) were determined in ~2 h of computer time, demonstrating that the crystal packing and the molecular conformation of medium-sized (MW ≈ 500) pharmaceutical compounds can now be solved quickly and routinely from high-resolution X-ray powder diffraction data.

J.M. Delgado et.al., (2007) 73 The characterization of several polymorphs of oxytetracycline hydrochloride, a commonly used antibiotic of the tetracyclines family, was carried out after its crystallization under different conditions: slow evaporation, rapid crystallization, and vapour diffusion with different solvents. The solvents used included water, ethanol, methanol, ether, ethyl acetate, toluene, dichloromethane and dioxane. The different products obtained were analyzed by X-Ray Powder Diffraction, NMR, FT-IR, and Thermal Analysis (TGA and DSC).

Biserka Cetina-Cizmek et.al., (2003) 74 Solid-state properties of piroxicam benzoate, an ester prod rug of piroxicam, were investigated. Samples were prepared by recrystallization from various organic solvents (toluene, ethanol, methanol, ethyl acetate and acetone). Recrystallized samples were characterized by means of FTIR, DSC, TGA, SEM and XRPD. DSC, TGA and XRPD methods confirmed that piroxicam benzoate crystallized in two pseudopolymorphic forms, A and B. Pseudopolymorphic form A was obtained by recrystallization from ethanol and methanol by slow cooling at room temperature and by rapid cooling in an ice-cold bath, and also from toluene by rapid cooling in an ice cold bath. Pseudopolymorphic form B was obtained by recrystallization from toluene by slow cooling at room temperature.

Arvind K. Bansal et.al., (2003) 75 this study deals with the generation and characterization of various solid-state forms of celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor. The drug was subjected to polymorphic screen using different solvents to explore the possibility of existence of different solid forms. N,N-Dimethyl acetamide (DMA) and N,N-dimethyl formamide (DMF) yielded solvates in 1:1 stoichiometric ratio. Quench cooling of the melt resulted in amorphous form of the drug. All these solid-state forms were characterized by thermoanalytical (DSC, TGA, HSM), crystallographic (XRD), microscopic (polarized, SEM), spectroscopic (FTIR), and elemental analysis techniques. Solubility and van't Hoff studies were carried out for their thermodynamic interpretation. Influence of morphology of different solid-state forms on flow behavior was also investigated. Molecular modeling studies were used to elucidate the interaction between solute and solvent molecules in the solvate.

Marcelo Antonio Oliveira et.al., (2010) 76 Thermogravimetry (TG) and differential scanning calorimetry (DSC) are useful techniques that have been successfully applied in the pharmaceutical industry to reveal important information regarding the physicochemical properties of drug and excipient molecules such as polymorphism, stability, purity, formulation compatibility among others. Verapamil hydrochloride shows thermal stability up to 180 °C and melts at 146 °C, followed by total degradation. The drug is compatible with all the excipients evaluated. The drug showed degradation when subjected to oxidizing conditions, suggesting that the degradation product is 3,4-dimethoxybenzoic acid derived from alkyl side chain oxidation. Assessing the drug degradation kinetics, the drug had a shelf life (t90) of 56.7 years and a pharmaceutical formulation showed t90 of 6.8 years showing their high stability.

Alok Tripathi et.al., (2010) 77 Rabeprazole sodium, a proton pump inhibitor, exhibits polymorphism and present article summarize the different polymorphic forms of rabeprazole sodium. Rabeprazole sodium exhibit polymorphism and ten crystalline polymorphic forms along with an amorphous form are reported in the literature. Polymorphism is meaningless unless solid physical properties exert an influence on biological activity, physiochemical properties or an industrial manufacturing method of the substance and therefore researchers have been attracted toward the development of new polymorphic form of rabeprazole sodium, study of correlation of process parameters such as type of solvent, volume of the solvent, sequence of addition, temperature, rate of agitation, pH of reaction mixture etc on the polymorphism and the study of impact of different polymorphic forms of rabeprazole sodium on the biological activity, physiochemical properties or an industrial manufacturing method.

Kalinkova et.al., (1996) 78 investigated polymorphism of azlocillin sodium, results of infrared spectroscopy, thermal analysis (combined thermogravimetry and differential analysis) and scanning electron microscopy confirm recrystallization of lyophilized azlocillin sodium from simple solvent acetonitrile causes polymorphic transformation. New polymorph obtained by crystalline form.

Michael j. Jozwiakowski et.al., (1996) 79 reported Lamivudine obtained as acicular crystals (form I, hydrate) from water or methanol and as bipyramidal crystals (form II, nonsolvated) from many nonaqueous solvents. Form II is thermodynamically favored in the solid state (higher melting point and greater density than form I) at ambient relative humidities. Solubility measurements on both forms versus solvent and temperature were used to determine whether entropy or enthalpy was the driving force for solubility. Solution calorimetry data indicated that form I is favored (less soluble) in all solvents studied on the basis of enthalpy alone. In higher alcohols and other organic solvents, form I has a larger entropy of solution than form II, which compensates for the enthalpic factors and results in physical stability for form II in these systems. The metastable crystal form solubility at 25 °C was estimated to be 1.2-2.3 times as high as the equilibrium solubility of the stable form, depending on the temperature, solvent, and crystal form.

C. Rodriguez-espinosa et.al., (1994) 80 investigated polymorphism of diflunisal in three polymorphs (I, II, and III forms) and a new crystal form (form IV) of diflunisal were prepared and characterized by powder X-ray diffractometry, DSC, hot-stage microscopy, IR spectroscopy, and dissolution studies. The mutual transition behavior of the polymorphs was investigated and the melting points and melting enthalpies were determined from DSC and thermo microscopy data. All forms first recrystallize to the more stable form (form I) and then melt at 210oC; only one weak transition peak was detected corresponding to transformation of form III to form I. Differences observed in IR spectra indicate that intermolecular hydrogen bonding occurs between hydroxyl and carbonyl groups and/or between fluorine atoms. Unexpectedly the dissolution rate of form IV was lower than that of the most stable modification form 1.

V. Agafonov et.al., (1991) 81 reported polymorphic forms of spironolactone, single crystals of two polymorphic and four solvated crystalline forms were obtained using different solvents. The morphology, symmetry, and crystallographic parameters were determined for all crystal forms except for the one obtained from methanol. The stability and transformation of each type of crystal were studied by DSC, TGA, and X-ray diffraction analysis. The structural data of three forms allowed the observation of the change of conformation of the molecules of spironolactone in the three different lattices.

El-Sayed et.al., (1983) 82 studied polymorphic forms of spironolactone in four forms, using melting point and aqueous solubility determinations, IR, DTA, PXRD and powder dissolution. Crystals from ethyl acetate had the lowest melting range, while from acetonitrile had the highest range. Infrared spectra were not useful in clearly distinguishing between the different forms. DTA curves indicated that were different from the original form of the drug. X-ray patterns were different in spacing (d) values and intensities of radiation absorption, confirming the presence of four different forms of spironolactone. The form from ethyl acetate had the highest dissolution rate, while from acetonitrile had the lowest rate.

Ranendra N. Saha, K.Venugopal, New, et. al., (2005) 83 simple and cost effective UV-spectrophotometric methods were developed for the estimation of Gatifloxacin in bulk and pharmaceutical formulations. Gatifloxacin was estimated at 286 nm in 100 mM phosphate buffer (pH 7.4) and 292 nm in 100 mM hydrochloric acid (pH 1.2). Linearity range was found to be 1-18 μg ml-1 (regression equation: absorbance = 0.0684 Ã- Concentration in μg ml-1 + 0.0050; r2 = 0.9998) in the phosphate buffer (pH 7.4) and 1-14 μg ml-1 (regression equation: absorbance = 0.0864 Ã- Concentration in μg ml-1 + 0.0027; r2 = 0.9999) in hydrochloric acid medium (pH 1.2). These methods were tested and validated for various parameters according to ICH guidelines and USP. The proposed methods were successfully applied for the determination of Gatifloxacin in pharmaceutical formulations (tablets, injection and ophthalmic solution). The results demonstrated that the procedure is accurate, precise and reproducible (relative standard deviation < 2%), while being simple, cheap and less time consuming and can be suitably applied for the estimation of Gatifloxacin in different dosage forms and dissolution studies.

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