I NEED ADVICE ABOUT TAKING LATANOPROST (XALATAN)

Ophthalmologist Carolina Valdivia, MD answers questions about taking Latanoprost (Xalatan) eye drops for controlling intraocular pressure in glaucoma patients.

A 69 year-old male from India writes:

Dear Dr. Valdivia,

I am 69 years old and I have been diagnosed recently with glaucoma. My doctor has prescribed Latanoprost eye drops. I take one drop in each eye. I have the following questions about taking this medicine.

Is it necessary to keep the eye-drop bottle in the refrigerator once it has been opened? It states on the label of the bottle that it can be stored at room temperature, but my doctor insists that I store it in the refrigerator.
My doctor has instructed me to apply the eye drops at night at a fixed hour. Is it absolutely necessary that I be punctual? After applying the eye drops can I engage in strenuous work? If so, after how long?
Should I continue taking the medication if I suffer from any ENT [ear, nose or throat] trouble, cough, cold, toothache, etc. or should I stop using it temporarily?

I look forward to your answer.

Thank you for writing and for visiting glaucoma-eye-info.com.

Carolina Valdivia, MD You have asked some excellent questions, ones about which I am sure many other people have similar concerns. You have been diagnosed with glaucoma and currently are taking eye drops (Latanoprost) to control your intraocular pressure. Your questions relate to using this medication to effectively maintain your intraocular pressure at levels that do not cause damage to your optic nerve.

Your first question relates to the storage temperature for your eye drops. Latanoprost (Xalatan) is a drug that is similar to components in our bodies known as prostaglandins. In this case, it is a synthetic prostaglandin. Additionally, Latanoprost (Xalatan) is classified as a prodrug, meaning that it must undergo chemical conversion by metabolic processes in the body before becoming an active pharmacological agent.

The effectiveness of this glaucoma medication can be reduced if it is exposed to temperature changes. It is very stable at temperatures of 2-8C (36-46F). It also is quite stable at temperatures below 25C (77F) after opening.

Living in India, temperatures likely exceed 25C. Thus, it would be a good idea for you to keep the Latanoprost (Xalatan) in the refrigerator, where you can be sure that it will be maintained at the optimum 2-8C temperature. This will ensure that the glaucoma medicine will be completely effective each time that you apply it. I suspect that this is why your doctor has been so insistent that you store it there.

Your second question relates to how punctual you need to be in applying the eye drops and if you can engage in strenuous work or exercise after taking them.

The answer to this question is simple. It is essential that you always take your glaucoma medication as directed. Latanoprost (Xalatan) has been tested extensively. This includes numerous studies designed to measure the responses of patients to different doses and concentrations over time. Taken together, these investigations have shown that Latanoprost (Xalatan) at the recommended dose is safe and fully effective for a 24-hour period. However, beyond this time frame, the drug loses its potency and effectiveness.

Remember, a normal intraocular pressure is one that does not cause damage to YOUR optic nerve. Glaucoma medicines like Latanoprost (Xalatan) are designed to lower elevated intraocular pressure so that it is within your normal range. In order for Latanoprost (Xalatan) to do its job, effective concentrations of this glaucoma medication must be maintained at constant levels. The technical term for this is the titer (pronounced “ty-ter”) of the medication. When the titer of Latanoprost (or other glaucoma medication) falls below effective levels, intraocular pressure will increase and potentially can cause additional damage to your optic nerve.

Does this mean that you must apply the eye drops at precisely the same moment each night? No, it does not. However, the eye drops should be applied within a 30-minute period surrounding the time that you took them the previous night. This means that if you applied them at 9:00 pm the night before, you should take your next dose between 8:45 pm and 9:15 pm, with the optimal time to take it being 9:00 pm. This will ensure that an effective titer of the glaucoma medication is maintained at constant levels and your intraocular pressure is effectively controlled.

You should rest about 15 minutes after applying the eye drops to ensure that they have been absorbed by your eye completely. You can engage in physical exercise once you have waited the 15 minutes after application. If your ophthalmologist has prescribed more than one type of eye drop for you to take, do not apply the second glaucoma medication until you allow 15 minutes for the first medication to absorb in your eye.

Your last question relates to whether you should stop using your eye drops temporarily when you have respiratory infections or a toothache.

It is vital that you continue taking the eye drops without interruption, unless your doctor instructs otherwise. Remember, we are talking about preserving your eyesight. You can recover from a cold or upper respiratory problem, but damage to the optic nerve is irreversible.

Studies have shown that about 4% of patients have reported the co-occurrence of upper respiratory infections or colds while taking Latanoprost (Xalatan). However, no direct link has been found, even in this 4% of patients, that implicates Latanoprost (Xalatan) in these infections. Keep in mind that 96% of patients do not report this as a problem. The same holds true for toothache. To date, there is one reported case. However, the person was taking four other medications at the time and no direct linkage to Latanoprost (Xalatan) was found.

It is important to understand that pharmaceutical manufacturers are required to collect and disclose data on all reported side effects associated with a medication. However, this does NOT mean that the medication caused the side effects in all cases. In many instances, the side effect simply is something that occurs independently but at the same time as taking the medicine. Nevertheless, by collecting these data, pharmaceutical companies are able to identify statistical anomalies. This means that they are looking for reports of certain side effects in the patient population that occur more often than would be expected by chance alone. These cases then are studied to determine if the medication at the prescribed dosage is or is not causing the side effect.

I strongly recommend that you do not stop using the eye drops, unless your ophthalmologist tells you to do so. If it appears that the medication is indeed causing an adverse side effect in you, she or he will be able to prescribe an alternative glaucoma medication for you to take so that your intraocular pressure will continue to be managed effectively.

Carolina Valdivia, MD

REFERENCE:

Sweetman SC. Martindale: The Complete Drug Reference, 36th Ed. London: Pharmaceutical Press, 2009:1882.

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My goal in answering your questions is to provide you with information, clear up misconceptions, and to explain options so that you can have an informed conversation with your doctor. However, under no circumstances should my response to your question be considered a substitute for ongoing consultation and examination with your doctor. Since I have not examined you, I only can speak in terms of generalities, whereas your doctor has sufficient clinical details to evaluate your case specifically.

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