We make suspensions, all day long, at Stacy’s Compounding Pharmacy for dogs, cats, children and even adults. But, exactly what is a suspension? Dictionary.com defines it as the state in which the particles of a substance are mixed with a fluid but are undissolved.
A suspension is a heterogeneous mixture (made up of two or more substances that are not chemically combined) where the fluid contains solid particles large enough for sedimentation (the tendency of particles to settle out).
Think of muddy water. Eventually, left undisturbed for a while, the mud will settle to the bottom and the water will be clear again. The particles may be visible to the naked eye, larger than one micrometer and will eventually settle.
The particles never dissolve, they just float around in the bulk of the solvent, floating around freely. The particles of a suspension will not pass through filter paper and will scatter a beam of light passing through. This is the Tyndall Effect.
The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible. The Tyndall effect was first described by 19th-century physicist John Tyndall. The amount of scattering depends on the frequency of the light and density of the particles.
What is a solution? This is two or more substances, but in this case the particle are dissolved and become solvent. There will be no settling. When you boil water, and add sugar, the sugar particles dissolve and will never settle out. Like in sweet iced tea. We use simple syrup (sugar, water, preservatives) in suspensions as well as Methyl Cellulose which acts as an emulsifier, preventing the separation of two mixed liquids because it is an emulsion stabilizer.
The smaller and lighter particles will suspend easily in these liquids and water. If the particles are larger, and heavier, they will need more viscous (a glutinous nature or consistency; sticky; thick) liquid to suspend into for longer times.
Suspensions allow you to add flavors to help mask the taste of the drug. Cherry, grape, bubblegum and for animals, bacon, beef, chicken, fish and liver are a few examples. As said, the suspension will eventually settle, leaving all the particles at the bottom. If, say pet owner, doesn’t vigorously shake the bottle, they will not be giving their pet the proper amount of drug.
This happens a lot. If something says shake well, you must SHAKE WELL. A trick is to lay the bottle on its side during non-use. This will let the settlement happen the length of the bottle and it’s much easier to re-suspend.