PREFORMULATION

PREFORMULATION: Preformulation commences when a newly synthesized drug shows sufficient pharmacologic promise in animal models to warrant an evaluation in man. These studies should focus on those physicochemical properties of the new compound that could effect drug performance and development of an efficacious dosage form. A thorough understanding of these properties ultimately provide a rationale for formulation design or support the need for molecular modification. Prior to starting preformulation studies, the physical pharmacist should meet with the principal investigators involved in that drugs of the compound and the proposed development schedule.

Need for preformulation:Need for preformulation Preliminary evaluation Molecular optimization Suitability of excipients Suitability of dosage form

Essential information helpful in designing the preformulation evaluation of a new drug Compound identity Structure Formulation and molecular weight Therapeutic indication Probable human dose Desired dosage form Bioavailability model Competitive products V. Potential hazards Initial bulk lots Lot number Crystallization solvent Particle size range Melting point % volatiles Observations VII. Analytical methods HPLC assay TLC assay UV/Visible spectroscopy Synthetic route Probable decay products VIII. Key dates

Bulk scale-up Toxicology start date Clinical supply preparation IND filing Phase-1 testing Objective of prefomulation: The objective of this phase is the quantification of those physical chemical properties that will assist in developing a stable, safe and effective formulation with maximum bioavailability . Principal areas of preformulation research : I. Bulk characterization Crystallinaty and polymorphism Hygroscopicity Fine partical characterization Bulk density Powder floe properties

II. Solubility analysis Ionization constant – P Ka P H solubility profile Common ion effect- K sp Thermal effects Solubilization Partition of co-efficient Dissolution III. Stability analysis Stability in toxicology formulations Solution state stability  P H rate profile Solid state stability  Bulk stability  Compatibility

I. Bulk characterization: Changes in bulk properties of solid form such as particle size, bulk density and surface morphology.  Comprehensive characterization of all preformulation bulk lots is necessary to avoid misleading predictions of stability or solubility, which depend on a particular crystalline form. Crystallinity Crystal habit  Description of outer appearance of crystal. Crystal lattice or internal structure Molecular arrangement with in the solid. Characterization of a solid form: Verifying that the solid is the expected chemical compound. Characterizing the internal structure and then , Describing the habit of the crystal. I. Bulk characterization

Different habits of crystals Platy Equant or Massive Bladed Needle or Acicular Tabular Prismatic

Outline of differentiating habit & crystal chemistry of a compound:Outline of differentiating habit & crystal chemistry of a compound

ii. Polymorphism Definition: Polymorphism is the ability of a compound to crystallize as more than one distinct crystalline species with different internal lattices. Types of polymorphism: Enantiotropic e g : Sulfur Monotropic eg : Glyceryl stearates

Analytical methods for characterization of solid forms: Method Material required/Sample Miroscopy 1mg Fusion methods 1mg ( Hot stage microscopy) Differential scanning calorimetry 2-5mg ( DSC/DTA) Infra red 2-50mg X-ray powder diffraction 500mg Scanning electron microscopy (SEM ) 2mg Thermal gravimetric analysis (TGA) 10mg Dissolution/Solubility analysis mg- gm

iii. Hygroscopity Many drug substances , particularly water soluble salt forms have a tendency to absorb atmospheric moisture. Adsorption and eqilibrium moisture content can be depend upon the atmospheric humidity, temp ., surface area, exposure and the mechanism for moisture uptake. e g :- Nacl Tests for Hygroscopicity : Gravimetry Thermogravimetric analysis(TGA) Karl fischer titration or gas chromatography. iv. Fine particle characterization: Bulk flow, formulation homogeneity, and surface area controlled processes such as dissolution and chemical reactivity are directly affected by size , shape and surface morphology of the drug particles.

Tests By light microscopy Stream counting devices(Coulter counter and HIAC counter). Brunauer , Emmett and Teller(BET) nitrogen adsorption for surface area measurement.  Each nitrogen molecule occupies an area of 16A 2 Surface morphology may be observed by SEM which serves to confirm qualitatively a physical observation related to surface area. V. Bulk density : Def : Bulk density is the ratio between a given mass of a powder and it’s bulk volume. Bulk density= True volume+ Void volume Bulk density of a compound varies substantially with the method of crystallization , milling or formulation . Once a density problem is identified it is often easily corrected by milling, slugging or formulation. Bulk density is of great important in 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. vi. Powder flow properties a. Free flowing b. Cohesive Measurement of free flowing powder is Compressibility % Compressibtility = ( ∫ t - ∫ 0 / ∫ t )* 100 ∫ t - Tapped density ∫ 0 - Initial bulk density Angle of repose are usually useless because of their lack of precision.

Compressibility and Flowability of pharmaceutical excipients % Compressibility Flowability 5-15 Excellent 12-16 Good 18-21 Fair-passable 23-35 Poor 33-38 Very poor <40 Very, very poor

II. SOLUBILITY ANALYSIS:Preformulation solubility studies focus on drug-solvent systems that could occur during the delivery of a drug to candidate. Eg:- A drug for oral administration should be examined for solubility in media having isotonic chloride ion conc. and acidic P H. Analytical methods : Useful for solubility measurements HPLC UV spectroscopy Fluorescence spectroscopy Gas chromatography For most drugs , RP-HPLC offers an efficient and accurate means of collecting solubility data. P ka D etermination Determination of dissociation constant of a drug. II. SOLUBILITY ANALYSIS

Tested with in a P H range of 1-10. Henderson- Hasselbalch equation provides an estimate of the ionized and un-ionized drug conc. a t a particular P H . For acidic compounds; P H = P ka + log [ionized drug/un-ionized drug] For basic compounds; P H = P ka + log[un-ionized drug/ionized drug] Analytical methods: The preferred method is the detection of spectral shifts by Ultraviolet or visible spectroscopy. Potentiometric titrations. ii. Effect of Temperature The heat of solution, ∆ Hs represents the heat release or absorbed when a mole of solute is dissolved in large quantity of solvent. Endothermic Exothermic process

Tested for temp. range 5⁰C, 25 ⁰C,37 ⁰C and 50 ⁰C. In S= -∆ Hs /R (1/T)+C S= molar solubility at temp. T(Kelvin) R= gas constant iii. Solubilization Limited experiment to identify possible mechanism for solubilization. Addition of co-solvent to aqueous system. Eg:- Ethanol , Propylene glycol, Glycerin. iv. Partition Co-efficient Measurement of a drugs’s liphophilicity . Contains Octanol /Water and Chloroform/Water systems. Def :- Ratio of un-ionized drug distributed between the organic and aqueous phases at eqilibrium . P o/w = (C oil/ C water ) equilibrium Provides liphophilic / hydrophilic nature of the drug .

v . Dissolution Dissolution experiment can help to identify potential bioavailability problems. Dissolution can be controlled by several physicochemical properties including chemical form, crystal habit , partical size, solubility, surface area, and wetting properties . Noyes-Whitney equation for finding out dissolution rate ; dc/ dt =DA/ hV (Cs-C) D- Diffusion co-efficient h- thickness of the diffusion layer at the solid-liquid interface A-surface area of drug exposed to dissolution media V-volume of media Cs-conc. of a saturated solution of the solute in the dissolution medium at experiment temp. C-conc. of drug in solution at time ‘t’

APPARATUS: Type-1 Paddle Type-2 Basket Type-3 Reciprocating cylinder Type-4 Flow through cell Type-5 paddle over disc Type-6 Cylinder Type-7 Reciprocating through holder

III. Stability analysis :III. Stability analysis 1 st quantitative assessment of chemical stability of a new drug It includes  s olution solid state experiment under conditions typical for the handling, formulation, storage and administration of a drug candidate Method of testing: By HPLC

i. Stability in toxicology formulations : Evaluate samples of the toxicology preparations for stability and potential homogeneity problems. Usually a drug is administered to the animals in their feed or by oral gavage of a solution or suspension of the drug in an aqueous vehicle. Water, vitamins , minerals(metal ions ), enzymes present in feed , which can severly reduce the shelf-life of a drug. Solution and suspension toxicologic preparations should be checked for ease of manufacturing and then stored in flame-sealed ampules at various temperature . ii. Solution stability Objective: Identification of conditions necessary to form a stable solution. These studies should include the effects of P H , ionic strength, co-solvent , light , temperature and oxygen. Solution stability investigations confirm decay at the extremes of P H and temperature . Eg:- 0.1N Hcl , Water and 0.1N NaoH all at 90⁰C .

Testing: Prepare stability solutions. Pour it in flint glass ampules, flame sealed to prevent evaporation. Stored at constant temperature. Some ampules may be stored at a variety of temp. to provide data for calculation. Other Tests: Light stability test. Oxidation test. i. With an excessive headspace of oxygen. ii. With an excessive headspace of an inert gas Helium, nitrigen . iii.With an inorganic anti-oxidant sodium metabisulfite . iv. With an organic anti-oxidant Butylated hydroxy toulene (BHT).

Finally an Arrhenius plot is constructed by plotting the logarithm of the absolute temp. InK = - Ea /R(1/T)+C Ea - activation energy - Ea /R- from slope C- constant of integration R- gas constant iii. Solid state solubility Objective: Identification of stable storage conditions for drug in the solid state and identification of compatible excipients for a formulation. Tests: DSC or IR analysis for the detection of polymorphic changes. In case of surface discoloration due to oxidation or reaction with excipients , surface reflectance measurements on tristimulus or diffuse reflectance equipment may be more sensitive than HPLC assay

DETERMINING BULK STABILITY PROFILE FOR A NEW DRUG CANDIDATE Storage condition 4 Weeks 8Weeks 12Weeks 5⁰C-Refrigerator 22⁰C-Room temp. 37⁰C-Ambient Humidity 37⁰C/75%RH Light box Clear glass Amber glass Yellow-Green glass No exposure(control) 50⁰C-Ambient Humidity -Oxygen headspace -Nitrogen headspace 70⁰C--Ambient Humidity 90⁰C-Ambient Humidity

PREFORMULATION RECOMMENDATIONS:PREFORMULATION RECOMMENDATIONS Upon completion of preformulation evaluation of a new drug candidate, it is recommended that a comprehensive report be prepared highlighting the pharmaceutical problems associated with this molecule. These reports are extremely important in preparing regulatory documents and aid in developing subsequent drug candidates.

Reference:Reference Leon lachman, Herbet A.Lieberman, Joseph L.K : The theory and practice of industrial pharmacy ,1986;3:171-196