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Particle Characterisation In LIFE SCIENCE I TECHNICAL BULLETIN ISSUE N°11 /JULY 2008 PARTICLE CHARACTERISATION IN EXCIPIENTS, DRUG PRODUCTS AND DRUG SUBSTANCES AUTHOR: HILDEGARD BRÜMMER, PhD, CUSTOMER SERVICE MANAGER, SGS LIFE SCIENCE SERVICES, GERMANY Particle characterization has significance in many industries. For the pharmaceutical industry, particle size impacts products in two ways: as an influence on drug performance and as an indicator of contamination. This article will briefly examine how particle size impacts both, and review the arsenal of methods for measuring and tracking particle size. Furthermore, examples of compromised product quality observed within our laboratories illustrate why characterization is so important. INDICATOR OF CONTAMINATION Controlling the limits of contaminating • Adverse indirect reactions: particles Particle characterisation of drug particles is critical for injectable are identified by the immune system as substances, drug products and excipients (parenteral) solutions. Particle foreign material and immune reaction is an important factor in R&D, production contamination of solutions can potentially might impose secondary effects. and quality control of pharmaceuticals. have the following results: It is becoming increasingly important for In order to protect a patient and to compliance with requirements of FDA and • Adverse direct reactions: e.g. particles guarantee a high quality product, several European Health Authorities. are distributed via the blood in the body chapters in the compendia (USP, EP, JP) and cause toxicity to specific tissues or describe techniques for characterisation organs, or particles of a given size can of limits. Some of the most relevant cause a physiological effect blocking blood chapters are listed in Table 1. flow e.g. in the lungs. TABLE 1. RELEVANT CHAPTERS IN COMPEDIA RELATING TO PARTICLE SIZE COMPENDIUM TITLE EP 2.9.19 Particulate contamination - Sub-Visible Particle EP 2.9.31 Particle Size Analysis by Laser Light Diffraction EP 2.9.37 Optical Microscopy EP 2.9.38 Particle - Size Distribution Estimation by Analytical Sieving USP <766> Optical Microscopy USP <786> Particle Size Distribution Estimation by Analytical Sieving USP <788> Particulate Matter in Injections USP <789> Particulate Matter in Ophthalmic Solutions USP <811> Powder Fineness JP 3.04 Particle Size Determination by optical microscopy for morphological appearance and shape of individual particles JP 6.03 Particle Size Distribution Test Preparation JP 10 Laser Diffraction Measurement of Particle Size JP 11/12 Powder Particle Size Determination LIFE SCIENCE I TECHNICAL BULLETIN 2 PARTICLE SIZE AND DRUG PERFORMANCE Particle size of drug substances and analyses of these products are essential by microscopy. pharmaceutical excipients have an to achieving a homogeneous product, • Prolonged storage caused a decrease influence on chemical and physical while optimal particle size and shape is in particle size resulting in increased behaviour. Particle size is therefore product dependent. agglutination. relevant for the behaviour of powders, • Prolonged storage caused a change granulates, creams, emulsions, liquids, Particle testing is specifically required in particle size of a drug, negatively etc. in relation to: during stability testing, prior to release impacting content uniformity. The effect of the drug into the market. In our is especially important in cases of low • Bioavailability laboratories, we have observed a few API to excipient ratio. • Flowability cases of altered solid products during • Adhesive strength stability testing. Similar examples can be related to liquid • Drying properties products. • Solubility • A decrease in particle size during • An emulsion separated into two phases • Filterability stability testing resulting in higher due to an increase of particle size. • Thermal conductivity weight as humidity adsorption • Changes in particle size of eye drops increased. were determined to have an influence Size analysis becomes particularly • Prolonged storage influenced crystal on bioavailability and biocompatibility. important with new drug delivery formats growth and modification of the active such as liposomes and nanoparticles. Size ingredient. This growth was confirmed PARTICLE SIZE ANALYSIS Several techniques are available for testing of particles. Table 2 gives an overview of available techniques and the range they work within. TABLE 2. CURRENTLY AVAILABLE PARTICLE SIZE ANALYSIS TECHNIQUES AND PARTICLE SIZE RANGE TECHNIQUE MIN [µM] MAX [µM] Laser Diffraction Measurement by Malvern Mastersizer 2000 0.02 2000 Scanning Electron Microscopy 0.5 5000 Optical Microscopy 1 10 Time of Flight 5 250 Air-Jet-Sieving 20 500 Mechanical Sieving 35 4000 The most common method for particle practice the particles are passed through In our laboratory, we use this instrument size distribution is the Laser Diffraction a focused laser beam, and these particles for dry powders as well as for well- Measurement. The laser diffraction scatter light at an angle that is inversely dispersed samples and solutions (e.g. method is suitable for highly accurate proportional to their size. The angular slurries or samples that need to be determination of particle sizes in a range intensity of the scattered light is then measured wet in order to achieve good of 0.02µm to 2000µm. The technique measured by a series of photosensitive particle distribution). Typical diagram of a is based upon the beam diffraction detectors. particle size distribution investigation is phenomenon (Fraunhofer diffraction). In shown in Figure 1. FIGURE 1. EXAMPLES OF PARTICLE SIZE DISTRIBUTION: 0.2 – 1 mm VOLUME (%) PARTICLE SIZE (µM) LIFE SCIENCE I TECHNICAL BULLETIN 3 FIGURE 1. EXAMPLES OF PARTICLE SIZE DISTRIBUTION: 5 – 20 µm VOLUME (%) PARTICLE SIZE (µM) In this example, two particle size classes For larger particles, analytical sieving powders. Our laboratory has established (e.g. 0.1 – 1 mm and 5 – 20 mm) are methods can be used. The European tests for various powders and granulates. shown. The actual measurement of the Pharmacopeia classifies powders number of particles in a given range and according to their fineness. Table 3 the cumulative curve is represented. summarizes the different types of TABLE 3. POWDER CLASSIFICATION ACCORDING TO EUROPEAN PHARMACOPEIA TYPE % SIEVE NUMBER % SIEVE NUMBER Coarse powder > 95 1400 ≤ 40 355 Moderately fine powder > 95 355 ≤ 40 180 Fine powder > 95 180 ≤ 40 125 Very fine powder > 95 125 ≤ 40 90 There are two main types of sieving: can be used to gain more information on the focus point of the stage micrometer Mechanical Sieving and Air-Jet-Sieving. the shape and structure of the particles. scale. Then the distance between Mechanical sieving is carried out by We utilize microscopy to describe the scales of the two micrometers stacking the sieves in ascending order of morphological appearance, shape, size is determined and the particle size is aperture size and placing the powder on of particles and their distribution in APIs calculated. Particle number can also be top of the sieves. With Air-Jet-Sieving, and excipients. Microscopic investigations calculated by counting particles within the powder is fluidized and collected by can generally be applied to particles of the grid of the micrometer. Figure 2 application of negative pressure. A wide 1µm and larger. Optical microscopy is illustrates a typical field of a membrane range of sieve sizes are described in USP, particularly useful for characterisation of filter carrying the particulate matter in a EP and JP. In general, our laboratories particles that are not spherical. parenteral solution. Several particles of conduct mechanical sieving for particles different shape are marked by an arrow. larger than 75µm and for smaller particles In order to measure particle size, an air-jet sieving or sonic sieving. ocular micrometer is inserted and a calibrated stage micrometer is placed at Should further characterisation of particles the centre of the microscope stage and be required, optical microscopy methods fixed in place. The ocular is adjusted to LIFE SCIENCE I TECHNICAL BULLETIN 4 FIGURE 2. PARTICULATE CONTAMINATION IN A PARENTERAL SOLUTION Optical microscopy can also be used to investigate particles surfaces for re-crystalization of drug products (e.g. patches). Typical recrystalization of an API observed during stability storage is shown in Figure 3. FIGURE 3. RECRYSTALIZATION OF AN API ON A PARTICLE SURFACE LIFE SCIENCE I TECHNICAL BULLETIN 5 The Environmental Scanning Electron While for conventional SEMs, samples Typical pictures of a filter surface and a Microscopy (ESEM), with integrated must be suitable for high-vacuum and selected particle are shown in Figure 4. Energy Dispersive X-ray microanalysis electroconductive. In contrast, using On the left, an overview image is shown (EDX) for high resolution imaging and ESEM, damp samples, greasy/fatty and with the distribution of particles (bright element analysis, is a new generation isolating materials can be observed at spots). By EDX it is possible to determine scanning electron microscope (SEM). high resolutions and analysed without the elemental composition of each ESEM allows for collecting information the otherwise necessary preparations. particle. On the right a detailed image of regarding particle size and shape. The image is achieved by secondary one selected particle is depicted which Consequently, this technique could be electrons (SE - topography contrast) or by shows its crystalline morphology.
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