Pre-Formulation Studies

A complete and concise informative data on pre-formulation studies

1. Pre- Formulation Studies Compiled By Vaibhav Tripathi Dr. Anil K. Sahu Dr. Deepak K. Dash

2. Pre- formulation Studies Pre-formulation testing is the first step in the rational development of dosage forms. It can be defined as an investigation of physical and chemical property of a drug substance alone and when combined with excipients. Drug performance, safety & stability are assessed by using pre- formulation studies (PFS) PFS are an important foundation tool early in the development of both API and drug products .

3. Pre- formulation Studies Study of physical properties of drugs like physical form , particle size, shape, density, wetting, solubility , dissolution, organoleptic properties and their effect on formulation , stability and bioavailability. Study of chemical properties of drugs like hydrolysis , oxidation – reduction, racemization, polymerization and their influence on formulation and stability of products .

4. Pre- formulation Studies Study of physical properties of drugs like physical form , particle size, shape, density, wetting, solubility , dissolution, organoleptic properties and their effect on formulation , stability and bioavailability. Study of chemical properties of drugs like hydrolysis , oxidation – reduction, racemization, polymerization and their influence on formulation and stability of products .

5. Pre- formulation Studies Objectives To optimize the delivery of drug thorough determination of physical, chemical properties of new drug molecule that affect drug performance and development of an efficacious stable and safe dosage form . PFS on a new drug molecule provide useful information for subsequent formulation of a physico-chemically stable and bio-pharmaceutically suitable dosage form.

6. Pre- formulation Studies Objectives To find out best possible synthetic route of producing the API with maximum yield. To design the suitable Toxicological strategic management protocol. To optimize API & drug product manufacturing processes To Develop analytical methods for QC & QA To Determine the most appropriate & compatible container / closure system for formulation.

7. Pre- formulation Studies Parameters for PFS Bulk Characterization Solubility Analysis Crystallinity Intrinsic Solubility Determination Polymorphism pKa Determination Hygroscopicity Partition Coefficient Fine particle characterization Dissolution Studies Bulk Density Common Ion Effect Flow Property Compression Property Physical Description Stability Analysis Organoleptic Properties Toxicological Studies Colour Solution Stability Odour Solid State Stability Taste Chemical Analysis Hydrolysis Oxidation Reduction Racemization Polymerization

8. Pre- formulation Studies Organoleptic Properties A typical pre-formulation program should begin with the description of the drug substance. The color , odour and taste of the new drug must be recorded using descriptive terminology . It is important to establish a standard terminology to describe such properties in order to avoid confusion among scientists using different terms to describe the same property.

9. Pre- formulation Studies Organoleptic Properties Colour odour Taste Off white pungent Acidic Cream yellow Sulfurous Bitter Tan Fruity Blend Shiny Aromatic Intense Odourless Sweet Tasteless

10. Pre- formulation Studies Bulk Characterization Crystallinity : Generally most of drugs exist in solid state. Very few are in liquid state like valproic acid and even less in gaseous form like some general anesthetics . A crystal structure is a unique arrangement of atoms in a crystal.

11. Pre- formulation Studies Bulk Characterization Crystallinity : Physical properties affected by the solid-state properties can influence both the choice of the delivery system and the activity of the drug, as determined by the rate of delivery. A crystalline particle is characterized by definite external and internal structures. Crystal habit describes the external shape of a solid material.

12. Pre- formulation Studies Bulk Characterization Crystallinity : Crystallization is invariably employed as the final step for the purification of a solid . The use of different solvents and processing conditions may alter the habit of recrystallized particles , besides modifying the polymorphic state of the solid.

13. Pre- formulation Studies Bulk Characterization Polymorphism : Many drug substances can exist in more than one crystalline form with different space lattice arrangements . This property is known as polymorphism . The different crystal forms are called polymorphs .

14. Pre- formulation Studies Bulk Characterization Polymorphism : When polymorphism occurs, the molecules arrange themselves in two or more different ways in the crystal; either they may be packed differently in the crystal lattice or there may be differences in the orientation or conformation of the molecules at the lattice sites.

15. Pre- formulation Studies Bulk Characterization Polymorphism : This property directly influences the chemical stability and solubility of an API. Moreover, it also affects the bioavailability parameter and development scheme of a formulation. Identification methods of polymorphism are- Optical crystallography , Hot 0stage microscopy X- Ray Diffraction, NMR , FTIR Thermal analysis

16. Pre- formulation Studies Bulk Characterization Hygroscopicity : Many compounds and salts are sensitive to the presence of water vapour or moisture. When compounds interact with moisture, they retain the water by bulk or surface adsorption, capillary condensation , chemical reaction and, in extreme cases , a solution (deliquescence). Deliquescence is where a solid dissolves and saturates a thin film of water on its surface.

17. Pre- formulation Studies Bulk Characterization Hygroscopicity : Moisture is also an important factor that can affect the stability of candidate drugs and their formulations . Sorption of water molecules onto a candidate drug (or excipient) can often induce hydrolysis. For example a primary amine, when mixed with lactose was apparently stable even when stored at 90°C for 12 weeks.

18. Pre- formulation Studies Bulk Characterization Hygroscopicity : However, when the experiment was carried out in the presence of moisture, extensive degradation took place . Other properties such as crystal structure, powder flow , compaction, lubricity, dissolution rate and polymer film permeability may also be affected by moisture adsorption.

19. Pre- formulation Studies Bulk Characterization Fine particle characterization : 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 behaviour . For example, the bioavailability of griseofulvin and phenacetin is directly related to the particle size distributions of these drug.

20. Pre- formulation Studies Bulk Characterization Fine particle characterization : It is now generally recognized that poorly soluble drugs showing a dissolution rate- limiting step in the absorption process will be more readily bioavailable when administered in a finely sub divided state than as a coarse material. Size also plays a role in the homogeneity of the final tablet . Optical & electron microscopy, sedimentation method, coulter counter method

21. Pre- formulation Studies Bulk Characterization Powder flow properties : The flow properties of powders are critical for an efficient tableting operation. A good flow of the powder or granulation to be compressed is necessary to assure efficient mixing and acceptable weight uniformity for the compressed tablets. If a drug is identified at the pre-formulation stage to be "poorly flowable”

22. Pre- formulation Studies Bulk Characterization Powder flow properties : T he problem can be solved by selecting appropriate excipients . The problem can be solved by selecting appropriate excipients. In some cases, drug powders may have to be pre-compressed or granulated to improve their flow properties.

23. Pre- formulation Studies Bulk Characterization Powder flow properties : Angle of Repose: The maximum angle which is formed between the surface of pile of powder and horizontal surface is called the angle of repose. For most pharmaceutical powders, the angle-of repose values range from 25 to 45°, with lower values indicating better flow characteristics. Tan θ = h / r

24. Pre- formulation Studies Bulk Characterization Powder flow properties : Densities: The ratio of mass to volume is known as density Bulk density: It is obtained by measuring the volume of known mass of powder that passed through the screen. Tapped density: It is obtained by mechanically tapping the measuring cylinder containing powder . True density: It actual density of the solid material.

25. Pre- formulation Studies Bulk Characterization Powder flow properties : Densities: Granule density: may affect compressibility , tablet porosity, disintegration, dissolution. Compressibility: "Compressibility" of a powder can be defined as the ability to decrease in volume under pressure and " compactability

26. Pre- formulation Studies Bulk Characterization Powder flow properties : Compressibility : as the ability of the powdered material to be compressed into a tablet of specified tensile strength. It can be used to predict the flow properties based on density measurement.  

27. Pre- formulation Studies Solubility Analysis Important goal of the pre-formulation effort is to devise a method for making solutions of the drug Orally administered drug must dissolve in the fluid of the GIT prior to absorption . A drug must possess some aqueous solubility for therapeutic efficacy in the physiological P H range of 1 to 8. For a drug to enter into systemic circulation and to exert therapeutic effect

28. Pre- formulation Studies Solubility Analysis it must be first in solution form. If solubility of drug substance is less than desirable, then consideration must be given to increase its solubility. However, knowledge of 4 fundamental properties is mandatory for solubility analysis of a new compound. Intrinsic Solubility Determination pKa Determination Partition Coefficient 4. Common Ion Effect

29. Pre- formulation Studies Solubility Analysis 1. Intrinsic Solubility Determination (Co) : The intrinsic solubility is the equilibrium solubility of the free acid or base form of an ionizable compound at a pH where it is fully unionized. The intrinsic solubility should be measured at two temperature 4 & 5°C to ensure good physical stability and to extend short term storage and chemical stability.

30. Pre- formulation Studies Solubility Analysis 1. Intrinsic Solubility Determination (Co) : The solubility of weakly acidic and weakly basic drug as function of PH can be predicted with help of equation S = solubility at given p H . So = intrinsic solubility of neutral form. K1 = dissociation constant for the weak acid. K2 = dissociation constant for weak base. S = So {1 + (K1/ [H+])} For weak acid. S = So {1+ ([H+]/ K2)} For weak base.

31. Pre- formulation Studies Solubility Analysis 2 . Dissociation Constant (pKa) : Many drugs are either weakly acidic or basic compounds and, in solution, depending on the pH value , exist as ionized or un-ionized species. The un- ionized species are more lipid-soluble and hence more readily absorbed. The gastrointestinal absorption of weakly acidic or basic drugs is thus related to the fraction of the drug in solution that is un- ionized.

32. Pre- formulation Studies Solubility Analysis 2 . Dissociation Constant (pKa) : The conditions that suppress ionization favor absorption. The factors that are important in the absorption of weakly acidic and basic compounds are the pH at the site of absorption, the ionization constant, and the lipid solubility of the un- ionized species. These factors together constitute the widely accepted pH partition theory.

33. Pre- formulation Studies Solubility Analysis 2 . Dissociation Constant (pKa) : The relative concentrations of un-ionized and ionized forms of a weakly acidic or basic drug in a solution at a given pH can be readily calculated using the Henderson-Hasselbalch equations : for base for acid  

34. Pre- formulation Studies Solubility Analysis 2 . Dissociation Constant (pKa) : Weakly acidic compounds (pKa< 4.3) absorb relatively rapidly ; Those with pKa values ranging between 2.0 and 4.3 absorb more slowly and strong acids (pKa> 2.4) hardly absorb. For bases, those with pKa values smaller than 8.5 absorb relatively rapidly Those with a pK a between 9 and 12 absorb more slowly

35. Pre- formulation Studies Solubility Analysis 3. Partition Co-efficient : Partition coefficient influences permeation of a drug across biological membrane . The lipophilicity of an organic compound is usually described in terms of a partition coefficient; log P, which can be defined as the ratio of unionized compound, at equilibrium , between organic and aqueous phases

36. Pre- formulation Studies Solubility Analysis 3. Partition Co-efficient : logP = Drugs having values of P greater than 1 are classified as lipophilic, whereas those with partition coefficients less than 1 are indicative of a hydrophilic drug .  

37. Pre- formulation Studies Solubility Analysis 3. Partition Co-efficient : logP = 0 means that the compound is equally soluble in water and in the partitioning solvent. If the compound has a log P = 5 , then the compound is 100,000 times more soluble in the partitioning solvent. A log P = – 2 means that the compound is 100 times more soluble in water, that is quite hydrophilic

38. Pre- formulation Studies Solubility Analysis 3. Partition Co-efficient : Application Recovery of antibiotics from fermentation broth. Extraction of drug from biological fluid for therapeutic monitoring. Absorption of drug from dosage forms. (Ointments, Suppositories, Transdermal patches ). Study of distribution of flavoring oil between oil & water in emulsion.

39. Pre- formulation Studies Solubility Analysis 4. Common Ion Effect: The common ion effect describes the effect on ​equilibrium that occurs when a common ion (an ion that is already contained in the solution) is added to a solution. The common ion effect generally decreases ​solubility of a solute . So, weakly basic drug which are given as HCl salts have decreased solubility in acidic ( HCl) solution .

40. Pre- formulation Studies Solubility Analysis 4. Common Ion Effect: To identify a common ion interaction, the intrinsic dissolution rate of hydrochloride salt should be compared between, Water and water containing 1.2%W/V NaCl in 0.05M HCl and 0.9%W/V NaCl in 0.05M HCl After this, if solubility is not decreased then drud can be desined in chloride salt, otherwise it should be eliminated.

41. Pre- formulation Studies Solubility Analysis For drug candidates, with either poor water solubility or insufficient solubility for projected solution dosage form, pre-formulation study should include limited experiments to identify possible mechanism for solubilization. Methods for Increasing Solubility: Change in pH Co-Solvency Solubilization by Surfactant Chemical Modification of drug

42. Pre- formulation Studies Chemical Analysis Chemical property indicates the degree of stability of new drug entity. Such property helps to set the parameter for handling formulation development, storage & mode of administration. Factors pertaining to chemical features of API 1. Hydrolysis 2. Oxidation 3. Racemization 4. Polymerization

43. Pre- formulation Studies Chemical Analysis Hydrolysis: Splitting of bonds & the addition of H and /or OH ion of water. Hydrolysis involves nucleophilic attack of labile groups eg : ester and amide . When the attack is by the solvent other than water, then it is known as solvolysis.  

44. Pre- formulation Studies Chemical Analysis Hydrolysis: Conditions that catalyze the breakdown are Presence of hydroxyl ion , hydride ion, divalent ion, heat , light, ionic hydrolysis , solution polarity and ionic strength, high drug concentration. Hydrolysis can be prevented by Adjusting the PH . As most of the potent drugs are weakly acidic or weakly basic in nature .

45. Pre- formulation Studies Chemical Analysis Hydrolysis: Formulate the drug solution close to it’s PH of optimum stability or by Addition of water miscible solvent in formulation or by Using optimum buffer concentration to suppress ionization or by Addition of surfactant such as nonionic, cationic and anionic surfactant stabilizes the drug against base catalysis or

46. Pre- formulation Studies Chemical Analysis Hydrolysis: the solubility of pharmaceuticals undergoing ester hydrolysis can be reduced by forming less soluble salts or ester of drug . eg : phosphate ester of Clindamycin or Store with desiccants, using complexing agents. Other examples are aspirin, anaesthetics (ester), barbiturates, chloramphenicol, ampicillin (amide)

47. Pre- formulation Studies Chemical Analysis 2. Oxidation: Second most common mechanism of degradation. Oxidation occurs in two ways I. Auto- oxidation II. Free radical chain process

48. Pre- formulation Studies Chemical Analysis 2. Oxidation: Reaction of any material with molecular oxygen producing free radicals by hemolytic bond fission of a covalent bond. These radicals are highly unsaturated and readily accept electron from other substance causing oxidation is called Auto-oxidation . Free radical chain process involves Initiation, Propagation , Hydro peroxide decomposition and Termination.

49. Pre- formulation Studies Chemical Analysis 2. Oxidation: Factors affecting oxidation process are oxygen concentration, light, heavy metals particularly those having two or more valence state (copper, iron, nickel, cobalt ), hydrogen and hydroxyl ion, temperature . Oxidation can be Prevented by reducing oxygen content Oxidative degradation of drugs takes place in an aqueous solution

50. Pre- formulation Studies Chemical Analysis 2. Oxidation: so the oxygen content can be decreased by boiling water or by storing the formulation in a dark and cool condition or By addition of an antioxidant/reducing agent / chain inhibitors of radical induced decomposition . Usually steroids, vitamins and antibiotics undergo oxidative degradation.

51. Pre- formulation Studies Chemical Analysis 3 . Racemization: The inter conversion from one isomer to another can lead to different P’cokinetic properties (ADME) as well as different P’cological & toxicological effect. Eg . L-epinephrine is 15 to 20 times more active than D-form, while activity of racemic mixture is just one half of the L-form . It depends on temperature, solvent, catalyst & presence or absence of light.

52. Pre- formulation Studies Chemical Analysis 4. Polymerization: It is a continuous reaction between molecules. More than one monomer reacts to form a polymer . Eg . Darkening of glucose solution is attributed to polymerization of breakdown product [5- (hydroxyl methyl) furfural]. Eg . Polymerization of HCHO to para -HCHO which crystallizes out from the solution.

53. Pre- formulation Studies Biopharmaceutical Classification System (BCS) The Biopharmaceutical Classification System is a scientific framework for classifying a drug substance based on its aqueous solubility & intestinal permeability under prescribed condition. The BCS is only applicable to immediate release, solid orally administered dosage forms, emulsions or suspensions designed to deliver drug to the systemic circulation.

54. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Drug products having a narrow therapeutic index are excluded from consideration for a BCS guideline. The aim of the BCS is to provide a regulatory tool for the replacement of certain BE studies by conducting accurate in vitro tests. BCS has gained importance worldwide as a drug product regulation tool For scale-up production and post-approval changes

55. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS Solubility: A drug substance is classified as highly soluble if the highest single therapeutic dose is completely soluble in 250 ml or less of aqueous media over the pH range of 1.2–6.8 at 37±1°C.

56. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS Solubility: In cases where the highest single therapeutic dose does not meet this criterion but the highest strength of the reference product is soluble under the aforementioned conditions, additional data should be submitted to justify the BCS-based approach .

57. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS Solubility: The sponsor is expected to establish experimentally the solubility of the drug substance over the pH range of 1.2–6.8 at 37±1ºC. At least three pH’s within this range, including buffers at pH 1.2, 4.5 and 6.8 , should be evaluated.

58. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS 2. Permeability: The assessment of permeability should preferentially be based on the extent of absorption derived from human pharmacokinetic studies, e.g., absolute bioavailability or mass balance . High permeability can be concluded when the absolute bioavailability is ≥85%.

59. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS 2. Permeability: High permeability can also be concluded if ≥85% of the administered dose is recovered in urine as unchanged (parent drug ), or as the sum of parent drug. Permeability can be assessed by validated and standardized in vitro method.

60. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS 2. Permeability: Cultured Caco-2 epithelial cell monolayers derived from a human colon adenocarcinoma cell line are widely used to estimate intestinal drug absorption in humans . Human in vivo data derived from published literature (bioavailability studies ) may be acceptable.

61. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS 2. Permeability: III.

62. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS 3. BCS Based Bio-waiver : A bio-waiver is an exemption from conducting human bioequivalence (in-vivo) studies. It is intended to reduce the need for in vivo bioequivalence studies i.e., it can provide a surrogate for in vivo bioequivalence.

63. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significant terms in BCS 3. BCS Based Bio-waiver : In vivo bioequivalence studies may be exempted if an assumption of equivalence in in vivo performance can be justified by satisfactory in vitro data .

64. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Class Solubility Permeability Examples Class- I High High Metoprolol , Propranolol, Diltiazem Class- II Low High Nifedipine , naproxen Class- III High Low Cimitidine , Metformin, Insulin Class- IV Low Low Taxol , Clorthiazole , Cefexime

65. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Class I Ideal for oral route administration. Drug absorbed rapidly. Drug dissolved rapidly. Rapid therapeutic action. Bioavailability problem not expected for immediate release drug product.

66. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Class II Oral route for administration. Drug absorb rapidly. Drug dissolve slowly. Bioavailability is controlled by dosage form and rate of release of the drug substance .

67. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Class III Oral route for administration. Drug absorbance is limited. Drug dissolve rapidly. Bioavailability is incomplete if drug is not release or dissolve in absorption window .

68. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Class IV Poorly absorbed by orally administration. Both solubility & permeability limitation. Low dissolution rate. Slow or low therapeutic action. An alternate route of administration may be needed.

69. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significance Regulatory toll for replacement of certain BE studies. It can save both time and money—if the immediate - release, orally administered drug meets specific criteria, the FDA will grant a waiver for expensive and time-consuming bioequivalence studies . Valuable tool for formulation scientist for selection of design of formulated drug substance .

70. Pre- formulation Studies Biopharmaceutical Classification System (BCS) Significance When integrated with other information; it provides a tremendous tool for efficient drug development . For research scientist to decide upon which drug delivery technology to follow or develop. Aid useful information in PFS if new drug entity.

71. References Brahmankar , D. M and Jaiswal , Sunil. B (2009). Biopharmaceutics and Pharmacokinetics – A Treatise. 2nd edition. Vallabh Prakashan , Page no. 27- 29 and 332 - 335 . WHO Prequalification of Medicines Programme; General notes on Biopharmaceutics Classification System (BCS)-based biowaiver applications ; Guidance Document October 2012 Kumar K.P. Sampath , A Text Book of Industrial Pharmacy (2019), Nirali Publication And Distributors , Maharashtra. ICH harmonized guideline “ Biopharmaceutics Classification System-based Biowaivers M9” Adopted on 20 November 2019