Eye drops are available mainly in two forms – as solutions and as suspensions.
Here is how we can describe a solution:
“A solution is a homogeneous mixture composed of only one phase. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. The solution more or less takes on the characteristics of the solvent including its phase.”
And here is how we can describe a suspension:
“A suspension is a heterogeneous mixture containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than one micrometer. The internal phase (solid) is dispersed throughout the external phase (fluid) through mechanical agitation, with the use of certain excipients or suspending agents.”
In short, the eye drop in the form of solution contains miscible constituents and does not need shaking before use. The eye drop in the form of suspension contains immiscible constituents and therefore needs shaking before use to deliver required concentration of the drug to the eye.
What would happen if you use a suspension eye drop (for example, Prednisolone Acetate) without shaking? Since the main ingredient is heavier than the fluid, it sediments at the bottom of the bottle. If you don’t shake the bottle, you will be administering only the fluid with a very tiny concentration of the main ingredient. As you use the eye drop, the concentration of the main ingredient will keep on increasing and it could be several times higher than the required dose when the bottle is about to exhaust.
This is not desired, especially if you are using a steroid (eg: Prednisolone) eye drop because steroid is supposed to be used in tapering dose – higher dose in the early part of the treatment and gradually decreasing dose spread over a few days or weeks.
So always shake the bottle of suspension eye drops vigorously before instilling it into your eye. If it is a solution eye drop, you don’t need to do so.
You can see the content of the bottle to know whether it is a solution or a suspension. A solution is a clear fluid whereas the suspension contains undissolved particles.
Why you may not be able to see whether it is a solution or a suspension:
1. The bottle is opaque (not transparent).
2. The bottle is transparent but the sticker/label on the bottle does not allow you to see the content properly. You can turn the bottle upside down and shake it to see if it is a solution or a suspension.
You can also confirm with your pharmacist or ophthalmologist.
If for some reason you are not sure whether it is a solution or a suspension, there will be no harm in shaking all your bottles before use.