Suspensions may be defined as preparations containing finely divided drug particles (the suspensoid) distributed somewhat uniformly throughout a vehicle in which the drug exhibits a minimum degree of solubility. Some suspensions are available in ready-to-use form, that is, already distributed through a liquid vehicle with or without stabilizers and other additives.
In most good pharmaceutical suspensions, the particle diameter is 1 to 50μm. Generally, particle size reduction is 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 50μm size is micropulverization. Micropulverizers are high-speed attrition or impact mills that are effi cient in reducing powders to the size acceptable for most oral and topical suspensions. For still finer particles, under 10μm, fluid energy grinding, sometimes referred to as jet milling or micronizing, is quite effective. By this process, the shearing action of high-velocity compressed airstreams on the particles in a confined space produces the desired ultrafine or micronized particles. The particles to be micronized are swept into violent turbulence by the sonic and supersonic velocities of the airstreams. The particles are accelerated to high velocities and collide with one another, resulting in fragmentation. This method may be employed when the particles are intended for parenteral or ophthalmic suspensions. Particles of extremely small dimensions may also be produced by spray drying. A spray dryer is a cone-shaped apparatus into which a solution of a drug is sprayed and rapidly dried by a current of warm, dry air circulating in the cone. The resulting dry powder is collected. It is not possible for a pharmacist to achieve the same degree of particle-size reduction with such comminuting equipment as the mortar and pestle.
Disperse systems having a consistency of a soft paste, gel, cream, or ointment can be conveniently packed into “collapsible tubes”, which are commonly made of:
Rubber of varying composition is used in pharmaceuticals and biologicals as:
The rate at which the equilibrium is achieved, is highly dependent in the details of the following:
These liquids are heterogeneous systems consisting of two phases:
A. By discipitation method
B. By precipitation method
This process is done by dispersing the finely divided powders in an appropriate liquid vehicle.
The use of surfactants is desirable to ensure uniform wetting of the hydrophobic surfaces.
This is performed by effecting precipitation in the liquid vehicle.
A. Organic Solvent Precipitation
— Water insoluble drugs are precipitated by dissolving them in a water miscible organic solvent. Then adding the organic phase to purified water under standard conditions.
B. Precipitation effected by changing the pH
— This is applicable to those drugs in which its solubility is dependent on pH value.
C. By Double Decomposition Method
— Where simple chemistry is involved.
— Example is the preparation of White Lotion USP (made by interacting zinc sulfate with sulfurated potash solution to form zinc polysulfide).
— Some incompatibilities that may occur in suspensions are: