1. Characteristics of drug include:
    • Physical description
    • Microscopic examination
    • Melting point
    • The Phase Rule
    • Solubility*
    • Dissolution*
    • Particle size*
  2. What did we find out about particle size and it’s impact on drugs?

    • Particle size affects solubility
    • Solubility affects dissolution
    • Dissolution affects absorption
  3. What can particle size affect?
    formulation and efficacy
  4. Content uniformity
    Particle size impacts the equal distribution of the active ingredient
  5. Physical and Chemical Properties Affected by Particle Size
    • Solubility
    • Bioavailablilty
    • Taste
    • Color
    • Stability
    • Dissolution rate
    • Content uniformity
    • Texture
    • Stability
    • Sedmentation rates
  6. Particle
    Unit of matter having a defined physical dimension
  7. Micromeritics
    Science and technology of small particles. Study of characteristics like particle size and distribution, shape, angle of repose, porosity and others
  8. Micromeritics Includes:
    • Particle size and size distribution
    • Pore size distribution
    • Particle shape
    • Particle surface area
    • Angle of repose
    • Porosity
    • Flow Properties- dusting powders
    • True and bulk volumes
    • Apparent density and bulkiness
  9. —Polydisperse particles:
    When a pharmaceutical powder contains particles of wide range of sizes and shapes, then it is called polydisperse sample
  10. Monodisperse particles:
    When a sample has particles of same size and shape, then the powder will be called monodisperse sample
  11. —Two most important parameters for pharmaceutical powders are:
    • The shape and surface area of individual particles
    • The size range and number or weight of particles present
  12. When the number or weight of particles of certain size range is plotted against the size range or particle size...
    a frequency distribution curve is obtained
  13. Two samples may have different distributions even though...
    their average diameter is the same
  14. How can particle size distribution be plotted?
    Using either weight or number of the particles
  15. —Equivalent Spherical Diameter:
    • This parameter is used to describe particle size of asymmetric particles.
    • Equivalent spherical diameter relates size of the particle to the diameter of a sphere having the same surface area, volume, or diameter
  16. —Surface diameter (ds)
    Diameter of a sphere having the same surface area as the particle in question.
  17. —Volume diameter (dv)
    Diameter of a sphere having the same volume as the particle in question
  18. —Stokes’ diameter (dst):
    Equivalent sphere undergoing sedimentation at the same rate as the asymmetric particle.
  19. —Projected Area Diameter:
    This is depicted as dimension 'C' and is the diameter of a theoretical circle, which would contain the same projected area as the irregular particle.
  20. —Aerodynamic Diameter:
    This is the diameter of a spherical particle that exhibits the same settling velocity in the air as the irregular particle
  21. Techniques to determine Particle Size:
    • Sieving!!!
    • Microscopy
    • Sedimentation
    • Coulter Counter
    • Dynamic Light
    • Scattering
    • Laser Diffraction
  22. Sieving
    • —Series of standard sieves
    • Used for grading coarser particles.
    • —The larger the mesh number the smaller the particle size of the powder
  23. Microscopy:
    • —Ordinary microscope is used to measure particle size in the range of 0.2 μm to about 100 μm.
    • Depth cannot be measured
  24. Sedimentation:
    —Particle size in the subsieve range may be obtained by gravity sedimentation as expressed in Stokes’ law Particle diameter corresponding to various time periods is calculated from Stokes’ law
  25. Coulter Counter
    The Coulter Principle states that amplitude of this pulse is directly proportional to the volume of the particle that produced it.
  26. —Principle of Laser Diffraction:
    • Light from a laser is shone into a cloud of particles (e.g. cement), which are suspended in a transparent gas (e.g. air)
    • The particles scatter the light
    • Scattered light measured by photodetectors. This is known as the diffraction pattern for the sample.
  27. Importance of Particle Size (surface area)
    • Affects the physicochemical properties of a drug and hence the pharmacological properties
    • —Affects the route of administration
    • —Formulation consideration – Flow, type, preparation
    • —Stability of formulation
    • —Dissolution and absorption characteristics
    • —Efficacy of therapeutic agent
  28. Particle Size also affects:
    • Physicochemical properties like bioavailability, dissolution rate, content uniformity, taste, stability, color and texture
    • —Affects flow and sedimentation rates
    • —Delivery of inhalation drug substance to the correct part of the lung at the correct dose
    • Packing of powders
  29. How does particle size affect surface area:
    • The smaller the size of a particle, the greater is its surface area
    • The greater the surface area, the better the dissolution
  30. When is dissolution most important?
    Absorption of drugs
  31. How do particles pass intestinal membrane:
    Dissolution: Only particles in the solution form pass intestinal membrane into systemic circulation for absorption
  32. What is the rate of absorption limited by?
    Rate of absorption for many slightly soluble drugs is limited by rate of dissolution
  33. When rate of solution is slower than the rate of absorption...
    then the dissolution process becomes the rate limiting step
  34. If you don’t remember anything else…
    Decreased Particle Size: Increases Surface Area

    Increased Surface Area: Increases Dissolution
  35. Particle size is an important factor when it comes to topical preparations because...
    • Reduced and uniform particle size makes the preparation smooth to touch and non-irritating
  36. Particles of different sizes lead to stratification which in turn leads to...
    inaccurate dosing
  37. For internal use, the finer the particle the higher the rate of dissolution thus improving...
  38. Particle size is an important factor when it comes to powders , tablets and capsules for the following reasons:
    • Free flow of powders to compress tablets
    • Content uniformity
  39. Pulmonary administration:
    • Drugs with particle size between 1 – 3 µm are deposited into the alveolar region
    • Larger particles deposit in the upper airways
    • Particles less than 0.5 µm are either expelled or inhaled
  40. Ocular suspensions formulas should...
    95% of the particles should have a size 10 micrometers or less
  41. Topical creams, ointments formulation:
    —Finely divided particles for better texture and feel
  42. Parenteral Formulations
    Particle size is of great importance due to possible problems with embolism and toxicity
  43. Comminution
    Mechanical process of reducing the size of fine particles or aggregates
  44. Comminution processes:
    • Manual – trituration, levigation, pulverization
    • Mechanical – grinders, coffee mills
  45. When should nonporous mortars be used?
    i.e. glass, when comminuting dyes and potent ingredients
  46. Trituration:
    • Continued rubbing of solids in a mortar with a pestle to reduce the size of the solid’s particles to a desirable degree of fineness.
    • Typically w/ dry particles
  47. There are 3 types of mortars and pestles:
    • Glass, wedgewood and ceramic
    • Glass mortars have smooth sides and so may not be as efficient in reducing particle size in comparison with ceramic and wedgewood
  48. —Levigation
    • Reduction in particle size by trituration or by spatulating on an ointment slab with addition of a non-solvent to form a paste
    • To improve ease of wetting, the solvent used is generally viscous with a low surface tension
  49. Pulverization by intervention
    • Used for compounds that cannot be easily triturated Drug is dissolved in a minimum amount of solvent
    • The solution is spread onto sides of a glass mortar or on an ointment slab as a thin layer and the solvent is allowed to evaporate.
    • The fine crystals are then scraped off the surface using a metal spatula
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