N-Acetylcarnosine Eyedrops for Cataracts in Dogs and Cats (Can-C, Bright Eyes NAC, etc)

A client recently asked for my opinion about the value of some over-the-counter eye drops purported to treat cataracts in dogs and cats. Not having read much about this product, I did a little research.

What Is It?
There are a number of eye drops marketed for prevention or treatment of cataracts in humans and pets. Most commonly, they contain a chemical called n-acetylcarnosine, which is made up of a couple amino acids and an acetyl group. In vitro research suggests this chemical has anti-oxidant effects, so it has been hypothesized to prevent or reduce the gradual opacification of the lens of the eye through this mechansism. As I have pointed out before, the role of oxidative damage in disease, and the value of anti-oxidant therapies, is a developing area of research. Many of the exuberant and enthusiastic hopes in this area have proven false, so while it is an area deserving further investigation, claiming something is an anti-oxidant is not automatic validation of its safety or benefits (e.g. 1, 2, 3).

Does It Work?
There have been a number of studies of n-acetylcarnosine, both in vitro studies and clinical trials in humans. Interestingly, almost all of these appear to have been published by the same researcher and his team, Dr. Mark Babizhayev. A clinical trial was published in 2001 (and it appears the same data was published again in a different journal in 2002, which if true is quite a significant science no-no). The trial was randomized and controlled in a small number of patients, and it appeared to show significant changes in a number of objective measures of cataract severity.

I am not familiar with the specific techniques used to measure the disease or response to treatment, so I will presume they are standard and appropriate measures for this kind of study. One thing that is not clear from the published report is whether the individuals making these measurements were blinded to the treatment status. This obviously has a significant bearing on the reliability of the results, especially when they stem from only one researcher, as such debacles as the Benveniste affair show.

A number of subsequent papers have been published by Dr Babizhayev and his team, mostly in vitro or lab studies investigating properties of n-acetylcarnosine, not clinical trials. Dr. Babizhayev has also become the leader of a commercial firm marketing n-acetylcarnosine for cataract treatment, and many other uses (including skin care, wound care, respiratory disease, and neurologic disease).

This commercial effort, and the spreading of claims for n-acetylcarnosine to a wide range of apparently unrelated applications, does raise some questions about the reliability of Dr. Babizhayev as the sole source of scientific validation for this compound. Overall, the status of the evidence for use of n-acetycarnosine for cataracts in humans is best summarized by the Royal College of Opthalmology:

 

The evidence for the effectiveness of N-acetyl carnosine eye drops is based on experience on a small number of cases carried out by a Russian researcher team. To date, the research has not been corroborated and the results replicated by others. The long-term effect is unknown.

Unfortunately, the evidence to date does not support the ‘promising potential’ of this drug in cataract reversal. More robust data from well conducted clinical trials on adequate sample sizes will be required to support these claims of efficacy.

Furthermore, we do not feel the evidence base for the safety is in any way sufficient

Unusually, there is actually some clinical trial evidence in veterinary species as well. An uncontrolled, unblended pilot trial has been published on an n-acetylcarnosine product (not the one Dr. Babizhayev sells) in dogs with cataracts.

David L Williams, Patricia Munday. The effect of a topical antioxidant formulation including N-acetyl carnosine on canine cataract: a preliminary study. Vet Ophthalmol. 2006 Sep-Oct;9(5):311-6. The results showed marginal improvement in all groups, though it was only significant in patients with 2 out of 5 types of cataract treated. However, subjectively owners reported improvement in 80% of the subjects.

Dr. Williams  has apparently performed a blinded, placebo-controlled follow-up trial on this product which did not show any benefits (in fact improvements were greater in the placebo group than in the treatment group), showing once again the importance of proper controls for bias, confounding, and other sources of error in clinical trials. Unfortunately, it appears unlikely this trial will be published for reasons which are not completely clear, though one implied issue is that journals are often reluctant to accept papers that show negative results, which are less exciting for readers than positive studies. All of this is, of course, through word-of-mouth among veterinarians, so I cannot confirm it is true.  

Is It Safe?
I have not found any reports of adverse effects from ophthalmic application of N-acetylcarnosine itself, and given its chemical makeup it seems unlikely to be hazardous. As usual, products containing this agent are not regulated as licensed medicines are, and there is no way to ensure label accuracy, proper manufacturing quality standards, or the safety of other ingredients that may be included with the N-acetylcarnosine. 

Bottom Line
The theoretical arguments for why this drug might be useful I the treatment of canine cataracts are plausible but largely unproven. There is limited clinical trial evidence in humans suggesting a benefit, but this has not been replicated and is at high risk of bias. The limited clinical trial evidence available in dogs does not suggest a benefit. There are minimal safety concerns with products containing N-acetylcarnosine.

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165 Responses to N-Acetylcarnosine Eyedrops for Cataracts in Dogs and Cats (Can-C, Bright Eyes NAC, etc)

  1. Laura O. says:

    They have certainly worked well for my dog! She is happier with her clearer vision now and I am happy knowing that Can C drops did/do the trick……at least for us.

  2. L says:

    Well, my dog had the cataract surgery on her remaining good eye. So, far all is going well.
    I don’t think any supplement would have helped at all (ridiculous)
    However, the surgery is expensive and complications can occur.
    So, I would have a consult with an ophthalmologist.
    I would never try phony baloney supplements, what a joke.

  3. L says:

    Update:
    My dog had the cataract surgery.

    Just want pet owners to know it is very expensive and complications can occur.

    So far it has cost double what I thought it would cost and follow-up may be lifelong.

    Yes, there have been complications, uveitis, fibrin development, additional treatments have been required.

    The good news. She can see!

    I am not sure I would have this done to another dog, couldn’t afford it anyway.

  4. L says:

    If possible would like to hear from a vet or two.

    How likely is fibrin development likely to reoccur, it has been blasted out (DAP) once already, 9 days postop.

    If the fibrin reoccurs what are my options? The rechecks are getting to be very expensive. Seven eye drops and one of them alone cost $127 .
    Prednisone taper and antibiotics continue.
    My regular vet has been helpful and I am hoping to transfer the follow up care to him as soon as the dog is stable.

    Anyone considering cataract surgery for their dog please talk to your vet and others that have gone through this.
    It is VERY EXPENSIVE and COMPLICATIONS can occur.
    Thanks n advance.

  5. L says:

    Positive news to report!

    My dog’s eye was rechecked today (15 days postop cataract surgery) by the covering ophthalmologist and all looks good! And she can see!
    No fibrin, in fact it was just mineral deposits that the last vet saw!
    Pressure is good, no significant inflammation. Yippee!
    I’ll stop complaining, I promise.

    Still, I don’t think I would ever do this again.
    Thanks for listening.

  6. L says:

    Oh, and I meant TPA regarding the fibrin mentioned in a previous post, not DAP

  7. L says:

    Update: The dog is doing well. It appears that the cataract surgery was a success!
    Eye drops (some of them expensive) and rechecks ($) continue…….

    Still, I would advise pet owners to proceed with caution if they are considering this
    elective surgery.

    Make sure you have plenty of money and nerves of steel 🙂

  8. Why are you so obsessed with studies? Didn’t all these people tell you they can see the difference in their dogs? Aren’t these claims equal to studies? When a dog can’t see and all of a sudden he sees!

    I have been taking n-acetyl-carnosine for my cataracts for several years. I was supposed to have surgery about 3 years ago. I’m still seeing fine!
    I had so much confidence that I bought Can-C and Vision Clarity Drops for my 14 year old beagle.

    I once had a doctor that told me don’t tell me about your vitamins, we didn’t learn that in school! DUH! I get better advice by reading Life Extension magazine.

    Nutrition.review.org says carnosine is a dipeptide consisting of 2 amino acids — alanine and histidine. It may help because it has antioxidant properties and inhibits glycation. It is not a poison! This article refers to a test done in 1997. One result was the elimination of existing cataracts.

  9. skeptvet says:

    I am “obsessed” with controlled research studies, as you put it, because I understand why our personal observations and assessments aren’t reliable. If we still relied on “I tried it and it seemed to work” as the standard of evidence, medicine would still consistent mostly of blood-letting, purgatives, and magic rituals, and most people would still die in childhood or childbirth or from now preventable or treatable diseases. Learning to doubt our experiences and test them with scientific methods has doubled our average life expectancy, dramatically reduced childhood and maternal mortality, and eliminated entire diseases (e.g. smallpox) that tortured people for thousands of years with no relief. Anecdotes mislead us all the time, and the fact that you don’t realize that is evidence of how deeply scientists and educators have failed to learn and teach the lessons of history. Here is more info, and a little humor, on the subject:

    Why Anecdotes Can’t Be Trusted

  10. JT says:

    Although most of the papers are by Babizhayev, they seem to be pretty reasonable. Summary scientific papers summarise that there is ‘promise’ for these drops and even that there is success in many cases. Studies such as Munday and Williams also suggest that there is a good deal of success.

    A point that was significant for me was that as well as the good rate of improvement, there was no worsening of the condition.

    It is not a replacement for surgery which for both eyes in the uk is usually £3500, plus the aftercare which commonly brings it up to £6000+. The surgery itself also brings risks, and not all cases are suitable.

    My Lhasa was diagnosed a few days ago and I am currently deciding what to do about it. The cataracts were probably as a result of her diabetes.

    If 75% of dogs go blind within the first 9 months of diabetes, and N-acetylcarnosine is doing what these papers report, it would be a good preventative for diabetic cataracts perhaps.

    I am seeing the vet today, and will get his/her opinion.

    I would just also say that Skeptvet seems to be giving a very big weight to an ‘unpublished’ follow up study that in his/her own words: ‘….All of this is, of course, through word-of-mouth among veterinarians, so I cannot confirm it is true. ….’.

    There does seem to be enough evidence from the existing papers and from anecdotal evidence to suggest that:

    a) There is a good chance that use of the N-acetylcarnosine based drops will lead to an improvement in vision.

    b) Use of the drops is safe.

    …but we need a proper study!! Apparently more trials are underway.

  11. Maryanne says:

    My 17 yr. Old shitsu on c,can drops 2 months, vet re checked eyes,today. Much improved, color returning, very clear. Playing again with toys. My dog now looks up,again at,me. Very GRATEFUL for this product.

  12. Sydney says:

    And almost every drug that is promising in theory and pre-clinical studies fails to make it to clinical use because of inadequate safety and efficacy. Over 90% of new therapies don’t work despite early promise, so trying just because some theories and treatments have turned out to work is ignoring the odds.

  13. Judy says:

    Please keep us posted.

  14. jeanne speir says:

    Dear skeptVet, a little evidence based practice humor where we all can find our niche.
    https://www.bmj.com/content/319/7225/1618

  15. skeptvet says:

    Yes, a classic!

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