Pharmaceutical Characterisation Dr. Lidia Tajber and Dr. Krzysztof Paluch School of Pharmacy and Pharmaceutical Sciences, Trinity College Dublin
Characterisation for Pharma Active pharmaceutical ingredients (API, drugs) Organic molecules, peptides, proteins Single components Mainly solids (crystalline, amorphous or semi-crystalline) Pure molecules Excipients (additives, fillers etc.) Organic, inorganic Not always single components Solids or liquids Not always pure Formulations (dosage forms, delivery systems) Mixtures of APIs and excipients Packaging materials
Characterisation for Pharma cont. Characterisation of properties that affect drug performance and development of efficacious dosage form preformulation A rationale for formulation design Support the need for molecular modifications of drug e.g. production of salt forms Studies of properties of drug and excipients during processing and storage formulation Changes caused by secondary processing e.g. milling, compression etc. Transformations occurring on storage impact of e.g. temperature, humidity Pharmaceutical characterisation can be extremely complex!!!
Critical issues in pharmaceutical solids Drug substance Drug+excipients Molecule Supramolecule Particle Granule Tablet Critical issue Critical property Impact on Molecular properties Supramolecular properties (crystal form) Particle properties (physical effects) Excipient effects Size of molecule Functional groups Lipophilicity, pka Pharmacological eff. solubility Crystal form Morphology, form size Type, properties and amount of excipients Solubility Dissolution rate Disintegration and dissolution rate Release Release Disintegration, Release Compaction pressure Disintegration and dissolution rate Disintegration, Release
Properties/Characterisation Confirmation of structure of API Fundamental/intrinsic properties of API Solid state properties of API Bulk properties of API API/excipient mix Nuclear magnetic resonance (NMR) Mass spectroscopy Elemental analysis Solubility Partitioning/distribution Melting/boiling points/sublimation Dissolution Polymorphism Solvation Crystallinity Particle habit/shape Particle size/distribution Density Surface area Flowability Compaction Stability/compatibility studies on API/excipient mix Solubility Dissolution Changes on processing
Methods of solid-state analysis Structural properties X-ray diffraction methods (powder, single crystal) Spectroscopy (UV, IR, Raman, solid-state NMR) Thermodynamic properties Thermal analysis, microcalorimetry, solubility determination, vapour pressure determination Moisture sorption Particle and bulk properties Microscopy and micromeritics
Application of PXRD analysis Non-destructive method Analysis of final dosage forms Distinguishing between solid-state forms of bulk drug substance polymorphs, solvated and amorphous forms An amorphous form does not produce a peak pattern Physical stability of formulation Quantitative determination of percentage crystallinity
Amorphous/Crystalline
Identification of solvates/desolvates 11000 9000 3000au 7000a) CTZK monohydrate half-ethanolate b) 5000 CTZK monohydrate (bulk material) c) CTZK 3000dihydrate d) CTZK 1000anhydrous e) 5 10 15 20 25 30 35 40 desolvated -1000 CTZK monohydrate half-ethanolate 2 θ degrees
in conjunction with thermal analysis a) 17 b) 12c) 2mg (TGA) CTZK monohydrate (TGA) CTZK dihydrate(tga) exo^ 24 14 CTZK monohydrate half-ethanolate(tga) d) CTZK anhydrous (TGA) 4 CTZK 7 monohydrate (TGA) e) CTZK dihydrate(tga) f) 2 CTZK g) monohydrate half-ethanolate(tga) -3 h) 10mW (DSC) -6-16 -26 CTZK anhydrous (TGA) -8 25 75 125 175 225 275 325 375 C -36 Source: Paluch KJ et al., Eur JPharm Sci 2011, 42, 220 229
Quantification of polymorphic forms Azithromycin -detection limit for Form II around 0.1% Source: LitteerB et al., Am Lab June 2005
Quantification of amorphous/crystalline content Calibration curve PXRD patterns Detection limit for the 0 10% amorphous phase is about 1% Source: LitteerB et al., Am Lab June 2005
Processing induced changes Influence of tableting pressure -finished tablets Source: LitteerB et al., Am Lab June 2005
Possible transformations of theophylline during wet granulation 1 2 Condition 1: temperature <60 C, low humidity (fast drying) Condition 2: temperature >60 C or interaction with moisture during drying (slow drying) Source: AiraksinenS et al., IntJ Pharm 2004, 276, 129 141
Problem of preferred orientation Anisotropic materials composed of crystals that are shaped like plates or needles E.g. aspirin crystallised from different solvents Crystal habit Infrared spectrum PXRD patterns Source: Pharmaceutical Analysis Lee D.C. and Webb M. eds., 2003
Dynamic vapour sorption (DVS) Water vapour or moisture sorption properties of pharmaceutical materials such as excipients, drug formulations and packaging are recognisedas critical factors in determining their storage stability processing application performance Moisture sorption properties are routinely determined for many pharmaceutical materials and have traditionally been evaluated by storing samples over saturated salt solutions of established relative humidities and then regularly weighing until equilibrium is reached Now process fully automated dynamic vapour sorption
DVS It is a gravimetric technique DVS analysis includes two humidity microbalance chambers one control one sample holder A sample is placed in a humidity microbalance and is exposed to predetermined level (or range) of humidity conditions at a presettemperature The control chamber is kept empty As the sample undergoes exposure the weight is recorded Also possible to use an organic solvent instead of water or a mix of solvents
DVS schematic of instrument http://www.thesorptionsolution.com/
DVS - application to the Pharma industry Humidity can influence material structures and behaviour -by exposing a sample to different levels of humidity it is possible to outline the optimum storage conditions Allows the determination of equilibrium moisture content at a range of temperatures and relative humidities Determination of hydrate and solvate formation Measurement of amorphous content
Changes upon hydration
coupled with PXRD 1000 au a) dihydrate raw material a) b) dihydrate, equilibrated at 10%RH b) c) dihydrate, equilibrated at 90%RH c) d) dihydrate, equilibrated at 70%RH d) e) monohydrate, equilibrated at 60%RH e) f) monohydrate, equilibrated at 0%RH (starting material: monohydrate) f) g) monohydrate, equilibrated at 0%RH (starting material: dihydrate) g) 5 10 15 20 25 30 35 40 Source: Paluch KJ et al., Eur JPharm Sci 2011, 42, 220 229
Detection of critical RH% of crystallisation Source: Paluch KJ et al., J Pharm Pharmacol in press
Kinetic studies
DVS Practical considerations: To fully characterise a sample several sorption and desorption cycles may be required e.g. not fully crystallising amorphous phases The choice of solventis important for analysis Materials which are not freely soluble in water are usually analysed with a an organic solvent vapour to induce crystallisation Octane is often used due to some similar structural traits to water Temperature. At a given temperature, the ratio of actual water vapour pressure/saturated water pressure at that temperature is termed the relative humidity (RH)
Advantages of DVS Much faster equilibration times -typically 10 to 100 times faster than traditional experimental approaches High precision and sensitivity -samples sizes less than 1 mg may be readily studied Sample preparation is fast and easy Full automation removes labourintensive nature of sorption measurements Flexible and easy to use computer interface -allows complex and novel experiments to be executed automatically without supervision It is possible to test the sample via XRD or DSC or Raman to investigate structural changes after DVS analysis
Limitations of DVS Each analysis is longand can be up to or over a week. It is dependent on number of relative humidity levels investigated and the time it takes to reach equilibrium moisture Sample may be physically changed due to moisture adsorption and DVS is considered a destructive analytical technique It is essential that the sample size is representative of the bulk but the larger the sample size the longer the test time
Inverse gas chromatography (IGC) IGC is a gas phase technique for characterising surface and bulk properties of solid materials Also known as Surface Energy Analyser (SEA) The principles of IGC are simple, being the reverse of a conventional gas chromatographic (GC) experiment In IGC a volume of gas or solvent vapour (a probe), carried by an inert gas, interacts with powder packed into a glass column Various probes interact with the powder differently thus a wide range of physicochemical properties of the solid sample can be measured
GC versus IGC http://www.thesorptionsolution.com/
IGC schematic http://www.thesorptionsolution.com/
IGC - principle Source: NiaziSK, Handbook of Preformulation 20007
Surface energy The injected gas molecules passing over the material adsorb on the surface with a partition coefficient K s K S = V N /m A sp V N is the net retention volume -the volume of carrier gas (He) required to elute the probe m is the weigh of the sample in the column A sp is the specific surface area of the sample in the column V N is a measure of extent of the interaction of the probe gas with the solid sample and is the fundamental data obtained from an IGC experiment The free energy of the surface is then calculated from V N and the dispersive free energy of the probe Source: NiaziSK, Handbook of Preformulation 20007
Milled and unmilled salbutamol sulphate Surface partition coefficients for milled (M1 and M2) and unmilled(u1 and U2) sample Source: FeeleyJC et al., IntJ Pharm 1998, 172, 89 96
Detection of transitions Retention behaviour of decane and dodecane on sucrose PVP (50:50 w/w) mixture. The discontinuous vertical line indicates the Tg. Retention behaviour of decane. Source: SuranaR et al., Pharm Res 2003, 20, 1647-1654
IGC Advantages: Gives a wide range of important material characteristics such as powder surface energies, acid/base/polar functionality of surfaces, solubility parameters and phase transitions Can be used with powders, fibersor films Limitations: Time consuming it may take between 20 to 30 hours for sample preparation and analysis Expensive-it requires several different solvents for analysis Very sensitive to atmospheric gases and may shut down if flammable gasses are even slightly detected with the analysis room Needs experience!