therapeutic insights
Star Antibiotics of 2003
Vigamox and Zymar live up to expectations.
By Bobby Christensen, O.D., F.A.A.O.

2003 has been a great year for new drugs in eye care and I'd like to review the two new topical antibiotic drugs that I feel are the top stars. The FDA approved Allergan's gatifloxacin ophthalmic solution 0.3% (Zymar) and Alcon's moxifloxacin ophthalmic solution 0.5% (Vigamox) last spring, so we now have some experience with the fourth-generation fluoroquinolones. The results have been nothing but positive.

Doctors want to know

Here are two of the most common questions I hear about the new fluoroquinolones:

1. Should we use these new antibiotics as our first line drug for prophylaxis and treatment? My answer is that we now have superior antibiotics that do a much better job killing Gram positive bacteria, so we must use the drug that has the best chance of healing the patient's eye infection. Use the new antibiotics for pre- and post-cataract surgery, before and after removing foreign bodies, treating conjunctivitis and, when warranted, going off label for microbial keratitis.

2. Will we create resistant strains of bacteria by using these topical drugs as a first choice? Possibly, but most bacterial resistance comes from use of oral or IV forms of the drug prescribed for systemic infections by other practitioners. Eyecare practitioners usually are not at fault when it comes to bacteria developing resistance to antibiotics.

New drugs hit the real world

Surgeons in Oklahoma City are using Zymar for preventing infection following cataract surgery, as well as post-op for laser vision correction. These surgeons changed to Zymar within a few weeks after it was available. To me, this indicates that they feel the most powerful antibiotic is the appropriate treatment for infection prevention.

Zymar has about equal protection against Pseudomonas aeruginosa when compared to the second and third-generation fluoroquinolones.

We've used Vigamox in our practice for treating bacterial conjunctivitis, bacterial keratitis and for prophylaxis before anterior segment procedures. I use Vigamox before suture removal, punctal plug insertion, drainage of lymphatic cysts, concretion removal and draining hordeolum. The three cases of microbial keratitis I've treated with it resolved within six days of treatment.

Vigamox is the only antibiotic drop that I'm aware of that doesn't contain a preservative. I'm not sure how important this really is because most courses of treatment are for two weeks or less; still, less toxicity to the epithelium is always appreciated, so it's a point you should consider when selecting an antibiotic. Vigamox is more soluble in ophthalmic formulation, meaning that it can be formulated in a higher concentration than previous fluoroquinolones.

Consider this

In recent years, of course, Gram positive bacteria, which cause a majority of eye infections, have gradually become more resistant to ciprofloxacin HCl 0.3% (Ciloxan) and ofloxacin 0.3% (Ocuflox). Staphylococcus and Streptococcus ocular cultures have exhibited strong susceptibility to Zymar and Vigamox, so we again have antibiotics that can likely control ocular Gram positive bacterial infections.

Time kill curves (TKCs) tell us how fast a medication eliminates most of the bacteria from the ocular surface. This is important because we often use antibiotics before we perform in-office procedures. The quicker the drug eliminates bacteria from the ocular surface, the less time we have to wait before performing the procedure.

The same principle applies to pretreatment before cataract surgery and LASIK. Vigamox, Zymar and Ciloxan all have good TKCs. Vigamox is best against Gram positive organisms (99.9% kill at 30 minutes) and Ciloxan is best against Gram negative organisms.

Penetration of the medication into the cornea and aqueous is another consideration when selecting between the antibiotics. At the Association for Research in Vision and Ophthalmology (ARVO) annual meeting this past May, one study gave us some comparisons: Penetration of one drop of Zymar into the cornea was 4.5 ug/ml at 30 minutes and 0.27 ug/ml in the aqueous at 60 minutes; penetration of one drop of Vigamox into the cornea was 12.5 ug/ml at 30 minutes and was 1.8 ug/ml in the aqueous at 30 minutes.

We all know that aminoglycosides cause epithelial toxicity, so I'm pleased to report that toxicity to the ocular tissue seems minimal with Vigamox and Zymar. Because Vigamox is unpreserved, it may be slightly less toxic to the ocular surface.

In conclusion

Allergan and Alcon have provided us with two excellent antibiotics. Infections caused by Gram positive bacteria were becoming increasingly difficult to cure, but we now have two antibiotics that have a strong Gram positive profile and a good Gram negative profile.

Additionally, these antibiotics have a fast kill time and are less toxic than many of the older antibiotics. Is there anything else I need to say to prove that these two drugs are our stars of the year for 2003?

Dr. Christensen has a partnership practice in Midwest City, Okla. He's a diplomate in the Cornea and Contact Lens Section of the American Academy of Optometry. He's also a member of National Academies of Practice.