Polymorph-Introduction Definition Physical properties of drugs Polymorph and it impact Solubility & Dissolution & Bioavailability & Pharmacology Polymorph testing

1. Importance of Polymorphism
in Pharma Industry
Dr. A. Amsavel, M.Sc., B.Ed., Ph.D.

2. Content
• Polymorph-Introduction
• Definition
• Physical properties of drugs
• Polymorph and it impact
• Solubility & Dissolution &
• Bioavailability & Pharmacology
• Polymorph testing
• Conclusion
• Reference

3. What is Polymorph?
• Polymorph has been derived from Greek word
– “POLY” means “many” & “MORPH” implying “form”.
• Polymorphism refers to different structural forms of a
chemical substance.
• Some of the chemical substances exist in two or more
crystalline forms with different arrangements or
conformations in the crystal lattice.
• Polymorphism is relevant to the fields of pharmaceutics,
agrochemicals, pigments, dyestuffs, foods and explosives.
• More than 50% of Drugs (APIs) are estimated to have
more than one polymorphic form .

4. History of Polymorph?
• The first observation of polymorphism is attributed to
Friedrich Wohler and Justus Von Liebig, in 1832.
• While cooling the boiling solution of Benzamide, found
different type of crystals.
• During cooling, initially the Benzamide was crystallized
in the form of silky needles, but on standing slowly
transformed into another form like rhombic crystals

5. Allotrope of Carbon
• Allotropes (Polymorphs) of Carbon
– Charcoal, diamonds and graphite, fullerene etc.
• Shows different crystalline structures and physical
properties,
Note: Structure determines the properties of the compounds

6. Allotrope of Sulfur
• Allotrope (Polymorphs) of Sulfur
– Sulfur forms over 30 allotropes, eg S6 S7, S8,
S12, S18 etc
S8-Cycloocta sulfur

7. Polymorphism
Polymorphism is the phenomenon where
crystalline forms of the same chemical compound
exist in different crystalline phases.
difference in
– internal crystal structure
– crystal packing arrangements
– molecular conformations.

8. Pseudomorphism
• When the solvent molecule are entrapped in the
crystal lattice of the solid are called as the
solvates.
– Mono hydrate, di, tri, penta, hexa……hemi, sesqi etc
– CaSO4⋅2H2O, CuSO4⋅5H2O , MgSO4⋅7H2O etc
• Solvates molecules will be in stoichiometry also
non-Stoichiometry
• The solvates can exist in different crystalline
form called as Pseudopolymorphs.

9. Molecule Arrangements in Solids
Hydrate/

10. Crystalline Structures

12. Chemical Compounds- Polymorph

13. Resorcinol- Polymorphs & properties
Rule Enantiotropic system Monotropic system
Polymorphic form α-form β-form
Fundamental definition Form-1 is the most stable
polymorphic form at
temperatures below the
transition point, while
Form-2 is the most stable at
above the transition point
Form-1 is the stable
polymorph at all
temperatures below that
of the melting point
Crystal class Orthorhombic Orthorhombic
Space group Pna Pna
No. of molecules per
unit cell
Z = 4 Z = 4
Unit cell axis lengths a=10.53 Å
b = 9.53 Å
c = 5.66 Å
a = 7.91 Å
b = 12.57 Å
c = 5.50 Å
Unit cell angles αβɤ=90° αβɤ=90°

14. Properties of Polymorphs
• Crystalline Solid shows differences in the
dimensions, shape, symmetry, capacity (number
of molecules), and void volumes of their unit
cells,
• Hence, have different in the bleow physical
properties due to differences in molecular
packing.
– molecular volume & molar volume
– Solubility, hardness, hygroscopicity
– density, refractive index
– thermal & electrical conductivity etc

15. Properties of Polymorphs
1. Packing properties
a) Molar volume and density
b) Refractive index
c) Conductivity (electrical and thermal)
d) Hygroscopicity
2. Kinetic properties
a) Dissolution rate
b) Rates of solid state reactions
c) Stability
3. Surface properties
a) Surface-free energy
b) Interfacial tensions
c) Habit (i.e. shape)

16. Properties of Polymorphs
4.Mechanical properties
a) Hardness
b)Tensile strength
c) Handling, flow, and blending
5.Spectroscopic properties
a) Vibrational transitions
• (Infrared absorption and Raman spectra)
b)Rotational transitions
• (Far infrared or microwave absorption spectra)
c) Nuclear spin transitions
• (Solid state nuclear magnetic resonance spectra)

17. Properties of Polymorphs
6.Thermodynamic properties
a)Solubility
b)Melting and sublimation temperatures
c) Vapour pressure
d)Internal energy (i.e. structural energy)
e)Enthalpy (i.e. heat content) , Heat capacity & Entropy
f) Free energy and chemical potential
g) Thermodynamic activity

18. Definition
• Bioavailability: Rate and extent of drugs (Active
Ingredient) is absorbed from a pharmaceutical form
and becomes available at the site of action. (measure
the concentration of drug in the blood/ uptake of drug
by the body)
• Solubility: Amount of chemical substance soluble in
specified volume of solvent ( g/ml in water or solvent)
• Dissolution: measuring time to dissolution of tablets
or capsules under standardized conditions, e.g.
artificial gastric juice

19. Definition
• Solubility: Amount of chemical substance soluble in
specified volume of solvent ( g/ml in water or solvent)
Descriptive term Approx. Volume of solvent in
g/ml of Solute
Very soluble Less than 1
Freely soluble From 1 to 10
Soluble From 10 to 30
Sparingly soluble From 30 to 100
Slightly soluble From 100 to 1000
Practically insoluble From >10000

20. Therapeutic Property
• Why do we take medicine?
Therapeutic purpose
• Medicine attempt to cure, improve, mitigate, treat
and/or prevent disease and/or other conditions ...
• Availability of medicine to the human body
(bioavailability) is based Solubility, permeability and
dose.
– The following properties of drugs influence the
bioavailability
– Physico-chemical properties, mechanical, thermal,
hygroscopicity, stability etc….

21. How Polymorph Affects the Efficacy
The majority of drugs are administered as solids.
• Physicochemical properties of drug substances influences the
therapeutic purpose
• Particle size and surface area affects the density, hardness
and compression characteristics .
Drug solubility:
• Form-I - 1g/10ml – dissolves more amount of drugs
• Form-II – 0.1g/10ml dissolves less quantity, less effective (less efficacy)
Drug dissolution rate Vs bioavailability
• Form-1 - 500mg tablet/30 minutes
• Form-II – 500mg /300 minutes

22. Impact of Polymorph
Physicochemical properties of drug substances will have
influence on the Efficacy
• Solubility, melting point, density, hardness and
compression characteristics
• Drug solubility and dissolution rate are based on Particle
size and effective surface area, hardness
• The variation in the abive properties also due to
Polymorphism and Amorphism, Pseudopolymorphism
(Stereochemical nature).
– Drug stability
– Lipophilicity of the drug
– pka of the drug and gastrointestinal pH

23. Stability characteristics
• Classified as two forms of Polymorphs based on relative
stability;
1. Stable form
2. Meta form
• Stable polymorph represents the lowest energy state, has
highest melting point and least aqueous solubility.
• Metastable form represent the higher energy state, have
lower melting point and high aqueous solubility.
• Metastable form converted to the Stable form due to their
higher energy state.
• Dissolution rate: amorphous > metastable > stable.

24. Types of Polymorphism
Two types of polymorphism
1. Monotropic polymorph
2. Enantiotropic polymorph
Monotrophs :
Only one polymorph is stable at all the temperature below the
melting point, with all other polymorphs being unstable.
• Eg. Chloramphenicol palmitate.
Enantitrophs :
If one form stable over certain pressure and temperature range,
while the other polymorph is stable over different pressure and
temperature range. Eg. Sulfur

25. Preparation of Ploymorph
A) Crystallization -From solution
 By using cooling techniques
 By using seeding techniques
 Evaporative crystallization
 By using anti-solvent
 Capillary crystallization
 Crystallization by using additives
B) Mechano-chemical methods
 Grinding
 Cryogenicgrinding
C) Other methods
 Thermal methods
 Sublimation
 Slurrying

26. Analytical Technique
Some of the Analytical techniques used to study crystalline forms
of the substances
1. X-Ray Powder Diffraction (XRPD)
2. Single crystal X-Ray Diffraction (XRD)
3. Thermal analysis :
– Differential Scanning Calorimetry(DSC),
– Thermogravimetry (TGA), Melting point & Thermomicroscopy
4. Moisture Sorption Analysis
5. Microcalorimetry
6. Optical Crystallography/ Hot Melt Crystallography
7. Scanning Electron Microscopy (SEM)
8. Solid-State Nuclear Magnetic Resonance (ss-NMR)
9. Spectrophotometry in the Infrared Region (FT-IR & Raman)

27. X-Ray Diffraction
• It provide the most complete information about solid state.
• This method is based on the scattering of X-Ray by crystal.
• In an x-ray diffraction measurement, a crystal is mounted on a
gonimeter and gradually rotated while being bombarded with
X-rays, producing diffraction pattern of regularly spaced spots
known as reflections.
• Identify the unit cell dimensions
• Crystal structure determination
• differences between polymorph
• Particle shape & size
• Phase identification & quantification
• 3D structure / imaging
• Contaminant detection and analysis

28. X-Ray Powder Diffraction (XRPD)- Alprazolam
0 b
XRPD- Alprazolam Form-I
XRPD- Alprazolam Form-II

29. X-Ray Powder Diffraction (XRPD)- Alprazolam
XRPD- Alprazolam Form-I
dobs (Å) I/Io (%) dcalc (Å) I/Ioca
lc (%)
hkl
11.04 1 11.014 1 0 0 1
9.25 100 9.205 100 0 1 0
7.27 67 7.236 64 0 1 1
6.93 14 6.900 14 0 1 1
6.86 10 6.826 11 1 0 0
6.70 <1 6.659 1 0 1 0
6.12 <1 1 0 1
5.90 73 5.871 70 0 1 1
5.57 2 1 0 1
5.56 <1 5.546 2 1 1 1
5.52 <1 5.501 1 0 0 2
4.85 29 4.828 28 0 1 2
4.79 35 4.769 34 1 1 0
4.64 20 4.631 26 0 1 2
4.63 81 4.599 80 1 2 0
4.62 4 0 2 0
4.56 8 4.541 10 1 1 1
4.54 2 1 0 2
4.41 43 4.388 41 1 1 2
4.34 19 4.321 18 0 2 1
4.30 7 4.278 7 1 2 1
4.24 17 4.225 11 1 2 1
4.19 10 4.177 10 0 2 1
4.13 <1 1 1 2
4.10 3 4.083 3 1 0 2
3.81 3 3.792 3 1 1 2
3.68 30 3.671 27 0 0 3
3.64 76 3.619 68 2 1 0
3.63 <1 0 2 2
3.58 23 3.569 20 1 2 2
3.56 3 3.537 4 2 1 1
Form I6 Form II6
Form III
Rietvelda
Form III
single crystala
Form III
HT-XRPDb
a(Å) 7.275(8) 7.414(10) 28.9339(9) 28.929(9) 29.34(4)
b (Å) 9.774(5) 13.806(4) 13.8548(3) 13.844(8) 13.92(2)
c (Å) 11.074(5) 15.269(4) 7.3540(1) 7.361(3) 7.826(11)
a (8) 90.80(3) 109.17(2) 90.00 90.00 90.00
b (8) 95.34(5) 92.15(6) 92.911(2) 92.82(3) 93.342(3)
g (8) 109.46(5) 93.03(6) 90.00 90.00 90.00
Z 2 4 8 8 8
V (Å3) 738.37 1471.67 2944.22 2944.46 3190.80
Dx
(g/cm3)
1.389 1.394 1.394 1.394 1.286
Comparison of Crystallographic Data for the Most Common
Crystalline Forms of Alprazolam
aAt room temperature data.
bFrom X-ray powder diffractogram measured at 225C.
The data are presented for d values until
an equivalent of 2Ɵ=25.

30. X-Ray Powder Diffraction (XRPD)- Alprazolam
XRPD- Alprazolam Form-II

31. DSC Analysis
Differential Scanning Calorimetric (DSC)
• DSC measures the amount of energy required to keep the sample at the
same temperature as the reference.
• sample and reference are maintained at the same temperature
throughout the experiment
• Measures the enthalpy changes due to changes in the physical and
chemical properties of a material as a function of temperature or time
Application:
• Characterizes thermal phase transitions & heat
of fusion and heat of crystallization.
Polymorph
– Melting, crystallization, Tg
• To determine specific heat capacity
• Assesses thermal stability -Degradation
temperature / quantity
• purity of relatively pure substances

32. DSC of Premafloxacin Form-I & III

33. DSC: Flunisolide

34. Thermogravimetric Analysis (TGA)
Thermal gravimetric analysis (TGA) is a technique in which the mass of a
sample is measured over time as the temperature changes.
• determine the change in weight as a function of temperature or time
• Obtain the weight loss curve
Applications
• to determine degradation temperatures
• thermal degradation
• melting point / Glass transition temperature(Tg)
• water content
• the level of inorganic and organic components
• heat of solvation / solvent content
• No. of polymorphs &ratio of each polymorph TGA 8000

35. TGA Curve of Efaverinz polymorphs

36. 0ptical Crystallography
 Crystals, are anisotropic nature, and their atoms are closer
together in some planes. Their optical properties are different
depending on which way the light travels through them.
 Recording the Image using polarizing microscope while heating
and cooling of crystalline form
 Isotropic and anisotropic crystalline form
can be identified
 Isotropic examine the velocity of light is
same in all direction.
 Anisotropic crystal have 2 or 3 different
light velocity or refractive indices.
Note: Isotorpic- Amorphous solid/ Glass ; Anisotropic- crystalline solid

37. 0ptical Crystallography
• Optically uniaxial crystals-tetragonal, hexagonal and rhombohedral: display double
refraction - two refractive indices one parallel to the optical axis and one
perpendicular.
• Optically biaxial crystals - exhibit three principal refractive indices orthorhombic
system.
• Optically biaxial crystals only one of the three optical axes monoclinic
• Optically biaxial crystals with no fixed and definite optical and crystallographic
axes, a triclinic system.

38. FT-IR Spectra: Carmazepine From-I,II&III
• FT-IR Spectra useful to identify the polymorphs due to changes in
frequencies, relative intensities, band contours and the number of bands.
• Difference in spectra gives an inference to the internal arrangement of
crystals

39. FT-Raman Spectra: Minaxolone Form-I&II
• Raman spectroscopy is analogous to FT-IR spectroscopy, useful to
study polymorphic form.
• Raman spectroscopy is better spectral selectivity than FT-IR

40. FT-Raman Spectra: Ranitidine

41. SS-NMR Spectra: Prednisolone

42. Polymorph at Drug Discovery

43. Screening of API

44. Conclusion
• Chemical purity and impurity of the API is not only adequate for
therapeutic use.
• One of the parameters influential in drug formulation is polymorphs
ie arrangements of molecule in crystal lattice
– impact physicochemical properties of the drugs
– affects the therapeutic purpose usage.
• Therefore, the study of polymorphic forms is important as like any
other quality parameters.
• Study of polymorph helps in selection and embark upon the proper
API/excipient
• pharmaceutical companies, as a part of their pre- formulation
studies, identify and study the stability of different polymorphs of
each potential new drug, while launching .

45. Reference
• Polymorphism in the Pharmaceutical Industry. Edited by Rolf Hilfiker-
Year 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
• Polymorphism in Pharmaceutical Solids-edited by Harry G. Brittain Center
for Pharmaceutical Physics © 2009 by Informa Healthcare USA, Inc.
• Polymorph Impact on the Bioavailability and Stability of PoorlySoluble
Drugs-Roberta Censi and Piera Di Martino Molecules 2015, 20, 18759-
18776;
• Polymorphism -The International Pharmacopoeia (Draft -July 2017)
• Guidance for Industry -ANDAs: Pharmaceutical Solid Polymorphism -
USFDA- Center for Drug Evaluation and Research (CDER) July 2007
• Vogel’s – Quantitative Chemical Analysis- 6th edition
• Principles of Instrumental Analysis- 6th Edition- D.A. Skoog et al
• Polymorphism of Alprazolam (Xanax1): A Review of its Crystalline Phases
and Identification, Crystallographic Characterization, and Crystal
Structure of a New Polymorph (Form III) . HE´CTOR NOVOA DE ARMAS, et
al. Wiley Inter Science (DOI 10.1002/ jps.20930

47. About Author:
Dr. A. Amsavel, born at Begarahalli, Dharmapuri-Dist, Tamil Nadu,
India. Completed his M.Sc. in Dept of Analytical Chemistry,
University of Madras. B.Ed. in Annamalai University and Ph.D in
Anna University, Chennai.
Worked as Lecturer and also worked in various Chemical &
Pharmaceutical Industries for the past 34 years. Presently working
as Assistant Vice President- Quality at Malladi Drugs &
Pharmaceuticals Ltd.