Slide 1: -- A case of learning before doing Pre formulation Dr. Raju Jukanti Slide 2: “A phase of a research and development process
where the pre formulation scientist characterizes
the physical, chemical and mechanical properties of
a new drug substance in order to develop stable, safe and effective dosage forms”. What is Preformulation? Introduction : Introduction Preformulation studies begin when a new chemical entity shows sufficient pharmacological promise and it may be a viable candidate for studies in man
Preformulation studies primarily include the study of the relevant physicochemical parameters for that dosage form and extensive stability studies so that the appropriate dosage form can be designed. Slide 4: What is Preformulation? Prior to nomination into full development, a candidate drug should undergo a phase traditionally called preformulation.
Preformulation is the physicochemical characterization of the solid and solution properties of compounds.
Preformulation testing encompasses all studies enacted on a new drug compound in order to produce useful information for subsequent formulation of a stable and biopharmaceutically suitable drug dosage form. Slide 5: Why is Preformulation Important? “Thorough Preformulation work is the foundation of developing robust formulations”
Good preformulation will inevitably lead to simple and elegant formulations and successful commercial products. Slide 6: Preformulation in the Overall R&D Process Slide 7: Framework for product development Slide 8: Bench scale -- 1/1000th of X
Lab scale -- 1/100th of X
Scale up -- 1/10th of X
Commercial -- X Stages of Formulation Development Slide 9: Goals of Preformulation To establish the physico -chemical properties of a new drug (API)
To establish the data on Drug- Excipient compatibility
To establish its (API) kinetic rate profile Slide 10: API / Excipient Characterization involves
Chemical characterization basically involves
Monograph or regulatory requirements
Identification tests (UV/HPLC/IR)
Limit tests (Heavy metals, sulphated ash, etc)
Physical characterization basically involves
Monograph as well as
Formulation dependent Preformulation Slide 11: Some commonly evaluated parameters Organoleptic properties
Particle size, shape and surface area
Partition coefficient, ionization constant and Kp
Crystal properties and polymorphism
Density, hygroscopicity, flowability, wettability etc.
Stability studies Organoleptic properties : Organoleptic properties Color – stability problems, improve appearance by including dye in body or coating.
Taste – palatability problems, flavors and excipients may be added.
Odor – degradation products, eg. Aspirin, stable form of drug to be used, flavors and excipients may be used. Suggested Terminology to Describe Organoleptic Properties of Pharmaceutical Powders : Suggested Terminology to Describe Organoleptic Properties of Pharmaceutical Powders Color Odor Taste
Off-white Pungent Acidic
Cream yellow Sulfurous Bitter
Tan Fruity Bland
Shiny Aromatic intense
Tasteless Purity : Purity Purity studies are essential for further studies to be carried out safely.
Impurities may make a compound toxic or render it unstable.
TLC, HPLC, GC and Paper chromatography used.
HPLC – Impurity Index (II) and Homogeneity Index (HI).
DTA, gravimetric analysis and melting point by hot stage microscopy are other techniques. Slide 15: Techniques used for characterizing purity
- Thin layer chromatography (TLC)
- High pressure liquid chromatography
- Gas chromatography (GC)
Impurity index (II) defined as the ratio of all responses (peak areas) due to components other than the main one to the total area response.
Homogeneity index (HI) defined as the ratio of the response (peak area) due to the main component to the total response. Slide 16: Example:
Main component - retention time: 4.39 min
- area response: 4620
Impurities - 7 minor peaks
- total area response : 251
Impurity index = 251/(4620 + 251)
Homogeneity index = 1 - 0.0515
= 0.9485 Slide 17: Other useful tools in assessment of impurity:
- Differential Thermal Analysis (DTA)
- Thermogravimetric Analysis (TGA)
- Differential Scanning Calorimetry (DSC)
- Powder X-Ray Diffraction (PXRD) Particle Size, Shape and Surface Area : Particle Size, Shape and Surface Area Various chemical and physical properties of drug substances are affected by their particle size distribution and shapes.
The effect is not only on the physical properties of solid drugs but also, in some instances, on their biopharmaceutical behavior
Size and Shape also influences the dissolution of poorly soluble drugs which in turn influences bioavailability.
Size and shape influence the flow and the mixing efficiency of powders and granules.
Size can also be a factor in stability.
Fine materials are relatively more open to attack from atmospheric oxygen, humidity, than that of the coarse material. Particle size Determination : Particle size Determination Microscopy is the simplest technique of estimating size ranges and shapes. e.g. Light microscope, Electron Microscope.
Andreason pipette is based on the rate difference of sedimentation of different particles, but techniques like this are seldom used due to their tedious nature.
Seiving methods are also used to measure particle size.
Instruments based on light scattering, (Royco), light blockage (HIAC) and blockage of electrical conductivity path (coulter counter) are available. Common Techniques for Measuring Fine Particles of Various Sizes : 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 Surface Area Determination : Surface Area Determination Surface area is most commonly determined based on Brunaver Emette Teller (BET) theory of adsorption.
Most substances adsorb a mono molecular layer of gas under certain conditions of partial pressure of gas( Nitrogen) and temperature
Air adsorption and permeability methods Slide 23: Solubility determinations The solubility of drug is an important physicochemical property because
The rate of drug release into dissolution medium and consequently, the bioavailabilty of the drug,
Therapeutic efficiency of the pharmaceutical product. Slide 24: How to determine Solubility ? Solubility is usually determined in variety of
commonly used solvents and some oils if the
molecules are lipophilic.
The solubility of material is usually determined
by the equilibrium solubility method Common solvents used for solubility determination : Common solvents used for solubility determination Benzyl Alcohol
Buffer at various pHs Water
Methanol Intrinsic solubility : Intrinsic solubility The solubility should ideally be measured at two temperatures.
The minimum density of water occurs at 4°C. This leads to a minimum aqueous solubility.
37°C to support biopharmaceutical evaluation . SOLUBILITY : SOLUBILITY Solubility > 1 % w/v
=> no dissolution-related absorption problem
Highly insoluble drug administered in small doses may exhibit good absorption
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 Slide 29: Solvent
(fixed volume) Adding solute in small
incremental amounts Vigorously
solute particles ? Examine
visually Yes No Total amount
added up Estimated solubility Semiquantitative determination: Accurately Quantitative determination : Accurately Quantitative determination Excess drug powder
150 mg/ml (15 %)
+ solvent Ampul/vial
(2-5 ml) Shaking at constant
(25 or 37 oC)
2 - 8 oC ? Membrane filter
0.45 mm Determine the drug
concentration in the
filtrate Determine the drug
concentration in the
filtrate Determine the drug
concentration in the
filtrate Membrane filter
0.45 mm Membrane filter
0.45 mm Same
concentration ? The first few ml’s of the filtrates should be
discarded due to possible filter adsorption Solubility 48 hr 72 hr ? hr Unique Problems in Solubility Determination of Poorly Soluble Compounds : Unique Problems in Solubility Determination of Poorly Soluble Compounds Solubilities could be overestimated due to the presence of soluble impurities
Saturation solubility is not reached in a reasonable length of time unless the amount of solid used is greatly in excess of that needed to saturation
Many compounds in solution degrade, thus making an accurate determination of solubility difficult
Difficulty is also encountered in the determination of solubility of metastable forms that transform to more stable forms when exposed to solvents PKa determination : PKa determination It is the negative logarithm of dissociation constant
It describes about the chemical nature of API/NCE.
It is mainly determined by using the Henderson – Hasseslebach equation For acidic compounds
pH = pKa + log (un-ionized drug) / ( ionized drug)
For basic compounds
pH = pKb + log (ionized drug) / (un-ionized drug) Slide 33: Partition co-efficient It is defined as the ratio of unionized drug distributed between
the organic and aqueous phases at equilibrium.
P o/w = (C oil / C water) equilibrium.
Partition Coefficient (oil/ water) is a measure of a drug’s lipophilicity and an indication of its ability to cross cell membranes.
Although partition coefficient data alone does not provide understanding of in vivo absorption, it does provide a means of characterizing the lipophilic/ hydrophilic nature of the drug.
The partition coefficient is commonly determined using an oil phase of octanol or chloroform and water.
If P much greater than 1 are classified as lipophilic, whereas those with partition coefficient much less than 1 are indicative of a hydrophilic drug. Slide 34: Many drug substance can exist in more than one crystalline from with different space lattice arrangements. This property is known as polymorphism.
Polymorphs generally have diffrent melting points, x-ray diffraction patterns and solubility even though they are chemically identical.
Different polymorphs also lead to different morphology, tensile strength and density of power bed which all contribute to compression characteristics of materials.Ex: Chloramphenicol palmitate-B form is more bio available than A&C Polymorphs.
Although a drug substance may exist in two or more polymorphic forms, only one form is theromdynamically stable at a given temperature and pressure. The other forms would convert to the stable form with time. Crystal properties and polymorphism Powder Flow Properties : Powder Flow Properties When limited amounts of drugs are available Power flow properties can be evaluated by measurements of bulk density and angle of repose.
Changes in particles size, and shape are generally very important.
An increase in crystal size or a more uniform shape will lead to a small angle of repose and a smaller Carr’s index. Bulk Density : Bulk Density Knowledge of absolute and bulk density of the drug substance is Very useful in Having some idea on the size of final dosage form
The density of solids also of affects their flow Properties Carr’s compressibility index can be used to predict the flow properties based on density measurement. Carr’s index (%) = ( Tapped density – Poured density ) * 100
Tapped density Angle of repose : Angle of repose “The maximum angle which is formed between the surface of a pile of powder and horizontal surface is called the angle of repose”. Relationship between powder flow, angle of repose, Carr’s index. : Relationship between powder flow, angle of repose, Carr’s index. Chemical stability profile : Chemical stability profile Preformulation stability studies are usually the first quantitative assessment of chemical stability of a new drug.
These studies include both solution and solid state experiments under conditions typical for the handing, formulation, storage, and administration of a drug candidate as well as stability in presence of other Excipients. Chemical stability profile : Chemical stability profile Solid state stability
Compatibility studies : stability in the Presence of excipients
Typical stability protocol for a new Chemical Entity. Solid state stability : Solid state stability Chemical instability normally results from either of the following reaction :-
Pyrolysis Solid state stability : Solid state stability Chemical structure of the drug is the determination of drug to either of these attacks.
Esters and lactase and to lesser extent, amides are prone to solvolysis .
Unstauration or electron rich centre in the structure make the molecule vulnerable for free radical mediated or photo-catalysed oxidation.
Physical properties of drugs such as Amorphous materials are less stable than their crystalline forms.
Denser materials are more stable to ambient stress. Elevated temperature studies : Elevated temperature studies The elevated temperatures commonly used are 40ºC, 50ºC, and 60ºC with ambient humidity.
The samples are stored at highest temperature are observed weekly for physical and chemical changes and compared to an appropriate control.
If a substantial change is seen, samples stored at lower temperature are examined .
If no changes are seen after 30 days at 60ºC, the stability prognosis is excellent . Stability under high humidity conditions : Stability under high humidity conditions Solid drug samples can be exposed to different relative humidity conditions by keeping them in laboratory dessicators containing saturated solutions of various salts.
The closed dessicators in turn are kept in oven to provide constant temperature.
The preformulation data of this nature are useful in determining if the material should be protected and stored in controlled low humidity environment or if non aqueous solvent be used during formulation Photolytic stability : Photolytic stability Many drugs fade on exposure light.
Though the extent of degradations small and limited to the exposed surface area, it presents an aesthetic problem.
Exposure of drug 400 and 900 foot-candles of illumination for 4 and 2 week periods respectively is adequate to provide some idea of photosensitivity.
Resulting data may be useful in determining if an amber colored container is required or if color masking dye should be used in the formulation Stability to Oxidation : Stability to Oxidation Drug’s sensitivity to oxidation can be examined by exposing it to atmosphere of high oxygen tension.
Usually a 40% oxygen atmosphere allows for rapid evaluation.
A shallow layer of drug exposed to a sufficient headspace volume ensures that the system is not oxygen limited.
Samples are kept in desiccators equipped with three-way stop cocks, which are alternatively evacuated and flooded with desired atmosphere.
The process is repeated 3 or 4 times to ensure 100% desired atmosphere.
Results may be useful in predicting if an antioxidant is required in the formulation or if the final product should be packaged under inert atmospheric conditions. Compatibility studies : Compatibility studies The knowledge of drug excipients interaction is useful for the formulation to select appropriate excipients.
The described preformulation screening of drug excipients interaction requires only 5mg of drug in a 50% mixture with the excipients to maximize the likelihood of obscuring an interaction .
Mixtures should be examined under nitrogen to estimate oxidation and paralytic effect at a standard heating rate on DSC, over a temperature range, which will encompass any thermal changes due to both the drug and appearance or disappearance one or more peaks in thermograms of drug excipient mixtures are considered of indication of interaction.