The College of Optometrists

Hi can anyone explain the difference between a preservative and an antimicrobial??

I always thought they were the same thing, yet on a bottle of 'Unpreserved' saline it stated that it contained antimicrobial agents??

This wasn't an aerosol type container, so it must have some sort of preservative. How can it be Unpreserved??

Any suggestions please??

there isn'y one. a preservative is a substance that inhibits microbe growth.

They are recognised as

chlorhexadine

benzalconium chloride

thimorosal

edta

benzyl alchohol

polyaminoprpyl biguanide

polyquad

sorbic acid.

as you notice from the list - several are toxic in high concentrations and bind to hydrogels causing increasingly high concentrations and toxic effects.

A true preservative free solution would be in a single dose pack.

But several salines are packaged as 'unpreserved' - they will have a shorter self life and care needs to be taken to control contamination. They will still have buffers etc. which still can cause allergy efects.

anti microbial means to me a substance that will reduce microbe populations by either inhibiting or killing the germs.

The unpreserved saline will be steriled during manufacture and the populations of germs within should stay low unless contaminated and/or kept longer than the use by date.

some use low concentrations of hydrogen peroxide, insufficient to meet the challenge required of a disinfectant but sufficient to act to provide the lower challenge of a preservative. The concentration is below the threshold for the eye to detect, and of course it breaks down into water and therefore will not cause an allergic reaction.

never heard of peroxide used as a preservative. Not in any drug-guides to saline etc either. do you know which solutions Martinc? I am very intrigued, I recall reading that at low concentrations H2o2 was not very efficient.

I think Ciba used sodium perborate, which produces up to .006 % h2o2. You will not see peroxide on the labelling, but perborate produces it.