a Stokes' equation does not apply precisely to the usual pharmaceutical suspension is irregularly shaped and of various particle diameters, in which the fall of the particles does result in both turbulence and collision and also in which the particles may have some affinity for the suspension medium
◼ Stokes’ equation does not apply precisely to the usual pharmaceutical suspension is irregularly shaped and of various particle diameters, ◼ in which the fall of the particles does result in both turbulence and collision, and also in which the particles may have some affinity for the suspension medium
The basic concepts of the equation do give a valid indication of the factors that are important to suspension of the particles and a clue to the possible adjustments that can be made to a formulation to decrease the rate of sedimentation a For the most part, the physical stability of a pharmaceutical suspension appears to be most appropriately adjusted by an alteration in the dispersed phase rather than through great changes in the dispersion medium
◼ The basic concepts of the equation do give a valid indication of the factors that are important to suspension of the particles and a clue to the possible adjustments that can be made to a formulation to decrease the rate of sedimentation. ◼ For the most part, the physical stability of a pharmaceutical suspension appears to be most appropriately adjusted by an alteration in the dispersed phase rather than through great changes in the dispersion medium
Physical Features of the Dispersed Phase of a suspension a The most important single consideration in a discussion of suspensions is the size of the particles. In most good pharmaceutical suspensions the particle diameter is 1 to 50 um. Particle size reduction is generally accomplished by dry milling prior to incorporation of the dispersed phase into the dispersion medium
Physical Features of the Dispersed Phase of a Suspension ◼ The most important single consideration in a discussion of suspensions is the size of the particles. ◼ In most good pharmaceutical suspensions, the particle diameter is 1 to 50 m. ◼ Particle size reduction is generally accomplished by dry milling prior to incorporation of the dispersed phase into the dispersion medium
One of the most rapid, convenient and inexpensive methods of producing fine drug powders of about 10 to 50 um size is micropulverization For still finer particles, under 10 um, fluid energy grinding get milling or micronizing) is quite effective Particles of extremely small dimensions may also be produced by spray-drying
◼ One of the most rapid, convenient,and inexpensive methods of producing fine drug powders of about 10 to 50 m size is micropulverization. ◼ For still finer particles, under 10 m, fluid energy grinding (jet milling or micronizing), is quite effective. ◼ Particles of extremely small dimensions may also be produced by spray-drying
The reduction in the particle size of a suspensoid is beneficial to the stability of the suspension However, one should avoid reducing the particle size too much, since fine particles have a tendency to form a compact cake upon settling to the bottom of the container. To avoid formation of a cake, it is necessary to prevent agglomeration of the particles into larger crystals or into masses
◼ The reduction in the particle size of a suspensoid is beneficial to the stability of the suspension. ◼ However, one should avoid reducing the particle size too much, since fine particles have a tendency to form a compact cake upon settling to the bottom of the container. ◼ To avoid formation of a cake, it is necessary to prevent agglomeration of the particles into larger crystals or into masses