Preformulation test for product development phase

1. PREFORMULATION AND PRODUCT
DEVELOPMENT
BISHNU PRASAD KOIRALA

2. Introduction
• Preformulation testing is considered as the first step
before rational development of the dosage form with a
drug molecule. It involves the exploitation of
biopharmaceuticals principles in selecting the right
excipient, right composition, right processing steps, and
right packaging materials. Obviously, the ultimate aim
is to design an optimum drug product which is cost
effective, safe, stable, patient-friendly and
therapeutically effective.

3. • So, the Preformulation testing is considered the
fundamental aspect of developing robust formulations
and can be considered as a learning process before
actually developing the dosage forms. The overall
objective of Preformulation testing is to gather enough
data in order to develop a chemically stable and
therapeutically effective drug product that can be
commercially produced at large scale.

4. Defination
• Preformulation study is defined as the stage of research
and development in which Preformulation studies
characterize physical and chemical properties of a drug
molecule in order to develop safe, effective and stable
dosage form.

5. Preformulation tests according to dosage form
Tests Dosage form
Organoleptic properties General *
Purity of API and excipient General *
Analytical method General *
solubility General *
Hygroscopicity Solid oral **
Ionization/dissociation constant
(pKa)
General *
Partition coefficient (Log P) General *
Dissolution behaviour Solid oral** , suspension

6. Preformulation tests according to dosage form
Tests Dosage form
Crystallinity and polymorphism General *
Particle size, shape and surface area Solid oral**
Bulk density Solid oral**
Powder flow property Solid oral**
Permeability General *
Stability General*
Drug excipient compatibility General*

7. Preformulation Parameters
Preformulation parameters Method used
Organoleptic Properties Colour and odour determination
Crystallinity & Polymorphism X-ray Diffraction Studies (Lachman, 1991)
Fine Particle Characterization Microscopic Method (Lachman, 1991)
Solubility Profile Equilibrium Solubility Method (I.P. 2007)
Solubilization (Lachman, 1991)
Analytical Method Development UV Spectroscopic Method, HPLC Method
Ionization Constant, pKa Determination of Spectral Shifts by UV Spectroscopy
(Lachman, 1991)
Partition Coefficient Using octanol / water,(Lachman, 1991)
Bulk Density Tapping Method (Lachman, 1991)
Powder Flow Properties % Compressibility Determination, Angle of Repose
(Lachman, 1991)
Compatibility With Excipient DSC (Stulzer and Rodriques et al., 2008)
Stability Solution and Solid State Stability (PCT/US03/35012)
Stability Indicating Method
Development
Forced Degradation Studies (Rao et al., 2009)

8. 1.Organoleptic properties
• “Organoleptic properties are those properties which are
evaluated after an impression on the organs of sense”
• It refers to the evaluation of drugs by properties like-
colour, odour, taste, size, shape and special features like
touch, texture. etc.. It is a technique of qualitative
evaluation based on the study of morphological and
sensory profile of whole drugs.

9. Some Organoleptic properties to describe an API
Colour Odour Taste
Off-white Pungent Acidic
Cream yellow Sulfurous Bitter
Tan Fruity Bland
Shiny Aromatic Intense
Odourless Sweet
Tasteless

10. 2.Purity of API and excipient
• Drugs are mainly available as solids, liquids, and gases.
Among these physical forms, solid drugs dominate the
market, followed by the liquid form. Solid materials are
preferred in formulation because of their ease of
preparation into solid oral dosage form such as tablet and
capsules. These solid drugs are pure organic compounds
that exist as either crystalline or amorphous. The purity
of the chemical substance is considered as its essential
quality to comply with various Pharmacopoeial tests
including therapeutic efficacy.

11. • Melting point of a chemical substance is considered its
intrinsic property which can be used as an indicator of
purity of that substance. As an example, a pure
crystalline API can be identified by its unique and very
sharp melting temperature determined by capillary
method. Apart from that method, purity of an API can
be determined by HPLC, TLC, DSC, or GC. In
chromatographic methods, reference standard of an API
is considered 100% pure and unknown samples are
compared against that reference standard.

12. Impurities found in common excipient
Excipient Impurity
Povidone, crosspovidone, polysorbates Peroxides
Magnesium Stearate, fixed oils, lipids Antioxidants
Lactose Aldehydes, reducing sugars
Benzyl alcohol Benzaldehyde
Polyethylene glycol Aldehydes, peroxides, organic acids
Microcrystalline cellulose Lignin, hemicelluloses, water
Starch Formaldehyde
Talc Heavy metals
Dibasic calcium phosphate dihydrate Alkaline residues
Stearate lubricants Alkaline residues
Hydroxypropylmethyl/ethyl cellulose Glyoxal

13. 3. Analytical method
• It is very important to develop and validate appropriate
analytical method at Preformulation stage. It helps to
quantify the API at various stages of product development,
especially during optimization of in vitro drug release
profile, product stability assessment, and drug-excipients
compatibility study. Depending on response of
chromophoric groups, UV spectrophotometric method is
firstly attempted, provided that excipients present in the
dosage form do not interfere with the detection at the
particular wave-length (λmax) of the drug.
• Suitable chromatographic methods such as HPLC, TLC, GC
may be used to avoid interference from excipients when
API is present with other excipients.

14. 4. Solubility
• The mainstream of existing drug candidates as well as
emerging NCEs are lipophilic i.e. poorly soluble in
water. This may be due to the high Crystallinity/melting
point and molecular weight of the drug or lack of
ionisable groups present in the molecule (Lipinski,
2001). However, the drug has to be in solution in order
to get absorbed through biological membrane, especially
at the gastro-intestinal tract (GIT). Without appropriate
solubilisation strategy, APIs with low solubility profile
are very thorny to design into solid oral dosage forms
due to their poor dissolution rate (tang et al., 2007).

15. Fig. Solubility of drugs as a function of pH, plotted as logarithm of the solubility
(adopted from Florence and Attwood, 2011).

16. • Most of the available drugs are weakly acidic and
weakly basic in nature and their solubilities increase in
basic and acidic pH respectively depending on their
ionization state.
• However, neutral drugs remain unaffected.
• Solubility > 1 % w/v
=> no dissolution-related absorption problem
• Highly insoluble drug administered in small doses may
exhibit good absorption

17. • Unstable drug in highly acidic environment of stomach,
high solubility and consequent rapid dissolution could
result in a decreased bioavailability
• The solubility of every new drug must be determined as
a function of pH over the physiological pH range of 1-8
• Intrinsic solubility is the solubility of a drug at a
particular temperature when the drug remains
completely in the unionized state. Apart from water, at
Preformulation stage, solubility study of active drug is
performed in various other solvents such as water,

18. Propylene glycol, polyethylene glycol, glycerin, ethyl
alcohol, sorbitol, methanol, isopropyl alcohol, benzyl
alcohol, polysorbates 20,80, castor oil, sesame oil,
peanut oil, and buffers at various pH depending on the
kind of dosage form to be developed.
Acc. to BCS system,
Class Permeability Solubility
Class I High permeability High solubility
Class II High permeability Low solubility
Class III Low permeability High solubility
Class IV Low permeability Low solubility

19. 5. Hygroscopicity
• Many substances, particularly water soluble salt form
have a propensity to absorb atmospheric pressure.
• Change in moisture level can manipulate chemical
stability, flowability, and compatibility. When
hygroscopic materials absorb adequate amount of water
where they get dissolved completely, as observed with
sodium chloride on a humid day; these are known as
deliquescent materials. Equilibrium moisture content of
any substance may depend on various parameters such
as humidity, temperature, surface area, exposure time
and the mechanism of moisture uptake.

20. • It can be monitored by Karl Fischer titration, TGA
• Depending on the Hygroscopicity of the drug, suitable
moisture-proof coating and storage in a low-humidity
environment or in a special packaging with a desiccant
can be adopted.

21. 6. Dissociation/Ionization constant (pKa)
• Dissociation or ionization constant (pKa) is defined as
the negative logarithm of the equilibrium coefficient of
the neutral and charged forms of a compound. The pKa
allows us to estimate the effective charge present on a
molecule at any particular pH.
• The unionized species are more lipid-soluble and hence
more readily absorbed.
• The GI absorption of weakly acidic or basic drugs is
related to the fraction of unionized drug in solution.

22. • Factors affecting absorption:
- pH at the site of absorption
- Ionization constant
- Lipid solubility of unionized species
“pH-partition theory”
Henderson-Hasselbalch equation
• For acids:
pH = pKa + log [ionized form]/[unionized form]
• For bases:
pH = pKa + log [unionized form]/[ionized form]

23. • Determination of Ionization Constant
1. Potentiometric pH-Titration
2. pH-Spectrophotometry Method
3. pH-Solubility Analysis

24. 7. PARTITION COEFFICIENT (Log P)
It is the ratio of unionized drug distributed between
organic and aqueous phase at equilibrium.
• P o/w = (C oil / C water) equilibrium
• It ratio of unionised drug in organic & aq. Phase
• It measure lipophilicity
• Major role in drug transport
• Analytical separation

25. • Partition coefficient is the ratio in which a solute
distributes itself between the two phases of two
immiscible liquids (mostly n-octanol /water) when they
are allowed to intimately mix with each other. As
shown below;

26. • The value of Log P measures the affinity of a drug
substance to partition between a lipid (oil) and
water. It is a useful parameter in predicting the in
vivo drug absorption through GIT or other
biological membranes. Factors such as absorption,
excretion and penetration of the drug through
diverse biological membranes are found to be
dependent on the Log P value of a drug. It also
helps in determining the membrane permeability,
plasma protein-binding, and volume of distribution,
renal and hepatic clearance.

27. 8. Dissolution behaviour
• Dissolution is a process which involves solubilization
of a drug after its release from dosage form before
being absorbed through the GIT membrane. It is a mass
transfer phenomenon from a solid surface to a liquid
phase. Dissolution rate may be defined as the amount of
drug substance that goes in solution per unit time under
standardized conditions of liquid/solid interface,
temperature and solvent composition. It may be
estimated by the Noyes-Whitney equation.

28. Fig: Dissolution and absorption of a drug from its solid dosage form.

30. 9. Crystallinity and Polymorphism
Solid drug substances may occur as amorphous and
crystalline forms. Amorphous drug has atoms or
molecules arbitrarily placed (without definite structure)
within it. Crystal is characterized by a highly ordered
arrangement of the molecules, connected with a three-
dimensional network. The repeating three-dimensional
patterns are ideally depicted as lattice. Crystal habit is
the description of the outer manifestation of a crystal.
Amorphous form is of a higher thermodynamic energy,
of greater solubility as well as higher dissolution rate
than the corresponding crystalline form. Many organic
drug substances can exist in more than one crystalline
form with different space-lattice considerate; this
property is called polymorphism.

31. • Solid crystal that contains entrapped solvent within its
structure is called solvate, also known as a pseudo-
polymorph. When the solvate is water, it is called a
hydrate. Aqueous solubility of hydrate compounds can
be considerably less than their anhydrous forms.
Characterization of a solid form involves
• verifying that solid is expected chemical compound
• Characterizing the internal structure
• Describing the habit of crystal

32. • Crystal habit: - A single internal structure may have
different habits depending on the environment for
growing crystals
• Internal structure: - Changes with internal structure
alter habit but chemical changes like conversion of salt
to free form changes both
• Amorphous – Many a times solute precipitates out of
solution so that the molecules in resulting solid are not
ordered in a regular array but in a more or less random
arrangement.
E.g.. By shock cooling, sudden change in solvent of
crystallization, lyophilization.

33. • thermodynamic energy solubility/ dissolution
rate
• But this form can be converted to crystalline form
due to bulk processing (e.g.. Tabletting)
• Crystalline – characterized by repetitious spacing
of constituent atoms/ molecules in a 3- D array
• It may contain either stoichiometric
(hydrate/solvate) or non stoichiometric
(clathrates) amount of crystallization solvent

34. • Polymorph: - Different crystalline structure, not isomer
Criteria for a compound to exist polymorphism
1. Two polymorph identical in liquid or vapour state
2. Polymorph on melting will give same composition
• Properties: m.p., solubility, density, hardness, crystal
shape, optical properties, electrical properties, vapour
pressure, stability changes

35. Crystal Morphology (Habit)
Habit Description
Acicular Elongated prism, needle like
Angular Sharp edged, roughly polyhedral
Bladed Flattened acicular
Crystalline Geometric shape fully developed in fluid
Dendritic Branched crystalline
Fibrous Regular/ Irregular thread like
Flaky/Platy Plate/ Salt like
Granular Equidimensional irregular shape
Irregular Lacking any symmetry
Nodular Rounded irregular shape
Prismatic Columnar prism
Spherical Global shape
Tabular Rectangular with a pair of parallel faces

36. 10. Particle Size, Shape, and Surface Area
• Particle size, shape and surface area of an API play
important roles for designing a solid oral dosage
form. Necessary characterization of these particle
properties is important at the Preformulation stage.
Certain physical properties (e.g. taste, texture, and
colour), chemical reactivity, stability,
bioavailability, content uniformity, sedimentation
rate, flow and mixing homogeneity of powders and
granules depend on particle size distribution and
shape.

37. Biopharmaceutical behavior also influence the flow and
the mixing efficacy of powders and granules. Fine
materials are relatively more open to attack from
atmospheric oxygen, humidity, than that of coarse
material.
Particle size determination
• Microscopy. Eg. Light microscope, electron
microscope.
• Anderson Pipette
• Sieving method
• Instruments based on light blockage(HIAC) and
blockage of electrical conductivity path(coulter
counter are available).

38. Common techniques for measuring fine particles
of various sizes
Technique Particle size (mm)
Microscopic 1 - 100
Sieve > 50
Sedimentation > 1
Elutriation 1 - 50
Centrifugal < 50
Permeability > 1
Light scattering 0.5 - 50

39. Shape determination
• Microscopy should be carried out to determine the ratio
of longest to shortest dimension. It is a shape factor.
SHAPE FACTOR
Commonly used shape factor converts volume of particle
‘v’ to its
volumetric mean diameter ‘av’
V=αv.av³
Shape factor may be defined which converts the surface
area ‘s’of
a particle to its surface mean diameter ‘as’
S=αs.as²
Fractal Dimensions are carried out by imaging techniques.

40. In(N)=-nIn(g)+q where:N=no.of squares.
g=length of grid
size.
n&q are
constants.

41. Surface area determination
• It is determined based on Brunaver Emitter Teller
(BET)theory of adsorption.
• Most substances adsorb mono molecular layer of gas
(Nitrogen) and temperature.
• Air adsorption and permeability methods.

42. 11. Bulk density
• Bulk density of powder drug is subjected to modify
during various manufacturing operation such as
milling, precipitation, crystallization or dry granulation.
Thus, knowing the bulk density is important when one
considers the size of a high-dose capsule product or the
homogeneity of a low-dose formulation in which there
are large differences in drug and excipient densities
(significant difference in the absolute densities of the
components could lead to segregation). Thus, size of
the finished product can be determined from such
information. The design and the capacity of mixer are
highly influenced by the bulk density of the powder.

43. Relation between Carr’s index and powder flow
property (adopted from Aulton, 2002)
Carr’s index Flow description
5 to 15 Excellent (free-flowing
granules)
12 to 16 Good (free flowing powdered
granules)
18 to 21 Fair (powdered granules)
23 to 28 Poor (very fluid powders)
28 to 35 Poor (fluid cohesive powders)
35 to 38 Very poor (cohesive powders)
> 40 Extremely poor (cohesive
powders)

44. 12. Powder flow property
• Exploration on powder flow property at Preformulation
stage is required to successfully manufacture tablet and
capsule dosage form. Based on the preceding knowledge
of flow properties of API and excipient (either alone or in
combination), a formulation recommendation such as
granulation or densification via slugging may be adopted.
One easy and quick method to estimate the powder flow
property is to resolve the angle of repose of that powder
sample. Angle of repose, it is defined as the maximum
angle possible between the surface of a pile of powder
sample and horizontal plane when the sample is poured
from a fixed distance.
tan θ=h/r
• Where θ = angle of repose, h = height of the powder pile,
r = radius of powder pile

45. Powder flow property depending on the angle of repose
value (adopted from Aulton, 2002)
Flow property Angle of repose (θ)
Excellent 25-30
Good 31-35
Fair-aid not needed 36-40
Passable-may hang up 41-45
Poor-must agitate, vibrate 46-55
Very poor 56-65
Extremely poor >66

46. • The pharmaceutical powders are classified as ---
Free Flowing
COHESIVE OR NON FREE FLOWING
• The powder flow are affected by the changes in –
Density
Particle Size Free flowing drug may become
Shape cohesive and necessitates
Electrostatic Charge an entirely new formulation
Adsorbed Moisture strategy

47. • Several rates of flow (g/sec) determinations at each of
variety of orifice sizes (1/8 to ½ inches) should be made.
• Greater the standard deviation between multiple flow rate
measurements greater is the weight variation in products
produced from the powder. It was found that the
dependence of flow rate (w) on the true particle
density(ρ),gravity(g), orifice diameter(D) by
D= A (4w/60πρ√g)^1/n
• A and n are constants dependent upon material and particle
size. Other measures of free flowing powders is
Compressibility.
%compressibility=(ρ1-ρ0)/ρ1
• Angle of repose is not much useful as lack of precision
• Cohesive Powders are characterized by Tensile Testing and
evaluated in a Shear Cell

48. 13. stability
• Drug degradation occurs due to chemical interaction
among drug and excipient or impurities present within
the excipient in presence of favorable environmental
conditions. However the structural features have lots of
influence on its decomposition (Crowley and Martini,
2001). There are some common pathways of
degradation such as hydrolysis, oxidation, photolysis,
isomerization and polymerization (Crowley and
Martini, 2001).

49. Product Stability Testing

50. Environmental storage conditions according to
climate zone. RH is relative humidity

51. 14. Drug-excipient Compatibility Study
• Study of drug-excipient compatibility is an important phase
in the pre-formulation stage of drug development. The
potential interactions between drugs and excipient have
effects on the chemical, physical, bioavailability and
stability of the dosage form.
• Excipient is substances which are included along with the
active pharmaceutical ingredient (API) in dosage forms.
Most excipient have no direct pharmacological action but
are important for facilitating the administration, modulating
the release of the active component and stabilizing API
against degradation. However, inappropriate excipient can
also give rise to inadvertent and/or unintended effects
which can affect the chemical nature, the stability and the
bioavailability of the API, and consequently, their
therapeutic efficacy and safety.

52. • Studies of drug-excipient compatibility represent an
important phase in identifying interactions between
potential formulation excipient and the API in the
development stage of all dosage forms.
Drug-excipient compatibility studies which focus on
three types of incompatibility:
• Physical incompatibility: We assess the change in the
physical form of the formulation, like color changes,
dissolution, solubility, sedimentation rate, liquefaction,
phase separation or immiscibility.
• Chemical incompatibility: We assess undesirable react
between API and excipient to monitor if compounds
undergo hydrolysis, oxidation, reduction, precipitation,
decarboxylation, and racemization.

53. • Therapeutic incompatibility: We assess the interactions
which are observed after administration of the medication.
Examples of biopharmaceutical interactions are premature
breakdown of enteric coat, interactions due to adjunct
therapy and increase in gastrointestinal motility.

54. Analytical Techniques Used to Detect Drug-
Excipient Compatibility
• Thermal methods of analyses
Thermal analysis plays a critical role in compatibility
studies and has frequently been employed for quick
assessment of physicochemical incompatibility. We
provide three different types of thermal analyses, which
include:
Differential scanning calorimetry (DSC)
DSC curves of pure components are compared to the
curves obtained from 1:1 physical mixtures. A
significant shift in the melting of the components or
appearance of a new exo/endothermic peak and/or
variation in the corresponding enthalpies of reaction in
the physical mixture indicate incompatibility.

55. • Isothermal microcalorimetry
It allows determination of minute amounts of evolved or
absorbed heat. The thermal activity of API, excipient and
their mixtures are measured individually in the calorimeter
and the thermal activity (heat flow) at a constant
temperature is monitored.
• Hot stage microscopy (HSM)
HSM is a visual thermal analysis technique, which allows
efficient monitoring of solid state interactions that could be
erroneously interpreted as incompatibility by DSC. This
technique only requires very small quantity of sample when
performing compatibility studies.

56. Spectroscopic techniques
• Vibrational spectroscopy
– FT-IR Spectroscopy
– Diffuse Reflectance Spectroscopy (DRS)
• Powder X-ray diffraction (PXRD)
PXRD is of great help for compatibility studies during
processes like compression, wet granulation, etc. and
bring on changes in crystallinity/amorphicity and
polymorphic forms of API in the presence of excipients.
• Solid state nuclear magnetic resonance spectroscopy (ss
NMR)
ss NMR has shown immense potential in the qualitative
and quantitative analysis of pharmaceutical solids.

57. • It has a unique advantage for detecting compatibility in
crystalline as well as amorphous components in a mixture.
Microscopic technique
• Scanning electron microscopy (SEM)
Chromatography
• Self-Interactive Chromatography (SIC)
• Thin Layer Chromatography (TLC)
• High-Performance Liquid Chromatography (HPLC)
HPLC exhibit a percentage loss of the API. We provide
liquid chromatography-mass spectrometry/mass
spectrometry (LC–MS/MS) to further characterize the
incompatibility products.

58. Conclusion
• Preformulation scientists act as intermediaries between
synthetic chemists and formulation scientists. With a
holistic aim of designing and developing a stable, cost-
effective and therapeutically sound patient-friendly
dosage form, they reduce the burden of formulation
scientist and help the pharmaceutical industries to
evade unanticipated consequences. The right selection
of API, excipients, dosage form, manufacturing
processes, packaging materials, analytical methods and
storage conditions among many others are important
for the benefit of the product’s life cycle and usage.