Solutions and Suspensions
solutions are sterile, free from foreign particles, and specially prepared for
instillation in the eye. Most ophthalmic solutions are dispensed in eye dropper
bottles. Patients should be shown how to properly instill the drops in their
eyes, and every effort should be made to emphasize the need for instilling only
one drop per administration, not two or three. When more than one drop is to
be administered, wait at least five minutes between administrations. Immediately
after instilling a drop on the eye, place pressure on the lacrimal sac for one
or two minutes. This will reduce the rate of drug loss through this pathway.
Ophthalmic suspensions are aqueous formulations that contain solid particles.
The particle size must be kept to a minimum to prevent irritation of the eye.
It has been recommended that particles be less than 10 microns in size to minimize
irritation to the eye. The micronized form of the drug can be used to meet this
requirement. There is a tendency of the solid undissolved particles to adhere
to the conjunctiva. As drug is absorbed, these solid particles will dissolve
to replenish the absorbed drug. This reservoir effect increases the contact
time and duration of action of a suspension compared to a solution.