Preservatives in Eye Drops
Chat Highlights – December 5, 2012
Guest Speaker – Dr. Michael Pro
Lorraine Miller, Editor, Chat Topic Researcher
Moderator: Good evening. The topic for this evening’s chat is “Preservatives in Eye Drops.” Dr. Michael Pro is joining us with his medical expertise.
P: What are the different types of preservatives used in glaucoma medication?
Dr. Pro: The most common preservative is benzalkonium chloride (BAK) which has been used for many years.
P: Why is BAK so favored as a preservative for glaucoma eye drops?
Dr. Pro: BAK is favored because it has an excellent safety profile. In other words, it does the job asked of it, namely to prevent the growth of harmful bacteria and fungi in multi-use ophthalmic medications. There are other preservatives but BAK is generally well tolerated and effective. A very small percentage of patients are allergic to this preservative, but that is not the main problem. The real problem is that BAK and other preservatives can cause ocular surface disease which is basically dry eyes.
It makes sense as the job of BAK is to kill bacteria, so in the same way, it is stressful to the corneal epithelial cells. It causes them to swell or shrink and this ultimately leads to an irregular corneal epithelial surface which can makes the eyes feel dry and scratchy and appear red.
P: How does a physician know if allergic reactions are caused from the preservatives in medication or the medication itself?
Dr. Pro: It used to be difficult to determine. In the past, we would ask patients to try different drops. Since most of the drops were BAK preserved, we assumed that if a patient’s symptoms were improved on a different agent then BAK was not to blame. Today, we have a host of non-preserved or alternately preserved medications. For instance, Travatan is a commonly used medication that is preserved with a unique non-BAK agent that is less toxic to the corneal epithelium. Alphagan P is also preserved with a non-BAK agent.
There are now glaucoma agents available which are completely preservative free. Timolol in Ocudose has been available for some time and now we have preservative free Cosopt PF and Zioptan. We can switch patients to these agents if they seem to have a rare BAK allergy, or more commonly, if they have ocular surface disease from the BAK.
P: On average, how long will preservatives keep glaucoma drops free of bacteria after a bottle is opened?
Dr. Pro: In general, a bottle should be disposed of about two months after it is opened. Truly preservative free medications come in single use vials and they must be disposed of on the same day that they are opened.
P: Does the type of preservative in the eye drop affect the length of time a bottle is bacteria free?
Dr. Pro: I do not know the answer. In general, bacterial contamination of multi-use in DROP-TAINERS® is very rare, so I would say that the preservatives are quite effective in their job.
P: What is done for the patient experiencing problems with preservatives?
Dr. Pro: There are now preservative free alternatives for almost all of the major glaucoma drug classes. Glaucoma lasers, like an SLT, are a good option for a patient who is on one drop but who does not tolerate that drop very well. Finally, surgery can help some patients whose glaucoma cannot be controlled with drops or who cannot tolerate the drops.
P: What problems occur because glaucoma eye drops were used prior to a trabeculectomy?
Dr. Pro: Great question. Some of you may be aware that in Europe there is a tendency to operate earlier. There may be some advantages to this as long-term drop use can lead to chronically inflamed conjunctiva and this can limit the ultimate surgical success of a trabeculectomy or other glaucoma surgery.
P: Is the damage that BAK causes to the eye reversible after filtration surgery?
Dr. Pro: In general, the changes that BAK causes to the corneal epithelium reverses after the BAK is stopped although it may take weeks to months for the dry eye symptoms to improve.
P: My eyes sting from using Betagan. Is the stinging due to the preservative? I had dry eye before starting any drops. What are the consequences of dry eye?
Dr. Pro: The stinging is common to many glaucoma drops and not always due to the preservative. For instance, some drops are pH neutral and some are slightly acidic or basic. As you can imagine, the further the drop is from pH neutral the more it may sting on instillation. Dry eyes can lead to irritation and blurred vision.
P: Are there any preservative agents that do not have the detrimental effects you mentioned above but just as good in preserving shelf life?
Dr. Pro: There are some preservative formulations that are gentler, such as the SofZia in Travatan and Purite in Alphagan P. Those are proprietorial formulations of Alcon and Allergan, respectively.
P: Do you find a certain proportion of the population more susceptible to the stinging of eye drops?
Dr. Pro: The stinging can affect all ages. However, dry eye is a very common problem and is more prevalent in older individuals and in perimenopausal and postmenopausal women.
Moderator: Thank you, Dr. Pro and everyone, for attending! Great chat tonight!