March 2008

 

OPHTHALMOLOGY NEWS

 

Enter Iquix


by Enette Ngoei EyeWorld Staff Writer

 

 

Surgeons welcome new treatment for bacterial corneal ulcers

It’s the only next-generation fluoroquinolone approved by the U.S. Food and Drug Administration for the treatment of corneal ulcers. John D. Sheppard, M.D., professor of ophthalmology, microbiology, and immunology, Eastern Virginia Medical School, Norfolk, who was involved in the clinical trials, calls it a step forward in topical ocular antimicrobial treatment. Just what is this new entrant to the fight against ocular infections? Its name is Iquix (Vistakon Pharmaceuticals, Jacksonville, Fla.), a 1.5% concentration of levofloxacin.

“It’s so highly concentrated that it’s self-preserved and doesn’t require a preservative in the bottle,” Dr. Sheppard said.

Iquix is potent and efficacious in the context of the most serious ocular surface infection, he said. “The levofloxacin molecule is derived from a unique approach to medication formulation, that is, it’s the L-isomer of ofloxacin, and biochemists will tell you that the L-isomer is the only bioactive isomer.” “The R-isomer is simply dead weight and excess baggage. In fact, the R-isomer decreases the solubility of the molecule without any antibacterial activity,” Dr. Sheppard said. Consequently, because of the tremendous solubility of the levofloxacin molecule, Iquix achieves a good penetration in the tissues and sustained release delivery is achieved.

“This results in a very large area under the curve that is the time and concentration first order integral of how much antibiotic a given tissue is exposed to in a given period of time.”

Furthermore, the high area end of the curve increases the potency of the drop and ensures that the concentration of the target tissues will be well above the minimal inhibitory concentration (also known as MIC) of relevant organisms throughout the period of therapy. This also compensates for the usual and customary digressions from ideal administration of the antibiotic such as forgotten doses or missed drops or drops that bounce off the cornea or drops that interfere with abnormal lid function, Dr. Sheppard said.

Studies have shown that there’s a high degree of variability in the amount of medication that gets into the tear film, the cornea, the anterior chamber, and even in highly controlled circumstances due to the idiosyncrasies of each patient and drop administrator. The assurance that the surgeon or the doctor treating ocular surface infection receives is therefore most welcome, he said.

In addition, the analysis of 11 years of antimicrobial susceptibility data collected by Tracking Resistance in the United States Today (TRUST), an ongoing nationwide surveillance program comprising 200 sites and more than 70,000 patients, showed no emerging resistance to levofloxacin.

Dr. Sheppard also said the highly concentrated formulation of levofloxacin shows no significant toxicities in animal models, wound-healing models, human healthy volunteer models, or in the clinical trial that led to the FDA approval of the drug. “So I’m very happy using the medication for my ulcer patients, for my ocular surface infection patients, for threatened glaucoma filtering bleb infections, for patients with severe conjunctivitis, patients with ocular surface surgery be it with DLK, PRK, PTK, significant ocular trauma, or foreign body removal,” Dr. Sheppard said.

Before Iquix, he used a smattering of antibiotics and ointments to get prolonged activity for foreign body removal or trauma. In some of his post-op situations or in peri-operative prophylaxis situations, he would use fluoroquinolones such as ofloxacin (Ocuflox, Allergan, Irvine, Calif.) or ciprofloxacin (Ciloxan, Alcon, Fort Worth, Texas).

In comparison, “The tremendous solubility [of Iquix] translates to much higher tissue concentrations and in the case of my keratitis patients, clearly a more rapid recovery with fewer drops,” Dr. Sheppard said.

James P. McCulley, M.D., professor and chairman, Department of Ophthalmology, University of Texas Southwestern Medical School, Dallas, said Iquix is three times the concentration of the commercial product and that it’s always good to have new antibiotics and new formulations available to surgeons. “There are different suggestions for designating things to ‘generations,’ and levofloxacin would be considered a third-generation fluoroquinolone. We now have two fourth-generation fluoroquinolones on the market that have broader spectra and penetrate quite well, at 0.3 for gatifloxacin [Zymar, Allergan] and 0.5 for moxifloxacin [Vigamox, Alcon] concentrations, so I’m really not sure exactly where [Iquix] would fit, except if I had a corneal ulcer with a patient that had an infecting agent with specific sensitivities to levofloxacin, I would prefer the 1.5 over the 0.5 concentrations,” Dr. McCulley said.

“When organism sensitivities dictate, then [Iquix] would be something I would be glad to have and prescribe. I don’t see it having any other role in my practice either for treating infectious disease or for prophylaxis given the availability of the fourth-generation fluoroquinolones. And of course the 1.5% levofloxacin is not product labeled for prophylaxis nor are the fourth-generation [fluoroquinolones],” Dr. McCulley said.

He continued: “If I have a good sense for what the organism is, either based on smears and stains at the time or culture results then that will drive my therapy specifically for the either presumed organism or the sensitivities once I have the organism identified.

“If I’m starting off with a shotgun, again it depends on the severity of the ulcer. If it’s a minor ulcer, I’ll start off with moxifloxacin with monotherapy. If it’s a very severe ulcer either threatening the visual axis and therefore vision or one that might perforate and therefore threaten the integrity of the globe, I’ll start off with a fortified aminoglycocide and cephalosporin, and I may or may not add moxifloxacin to that.”

It may not be a revolutionary product, but Iquix is certainly a welcome addition to the armamentarium that ophthalmologists have today, said Joel K. Shugar, M.D., M.S.E.E., Perry, Fla.“I think that there is a niche for it particularly if it’s priced economically,” he said.

Currently, in his practice, Dr. Shugar said it’s been a long time since he’s seen a corneal ulcer, but for a mild corneal ulcer, he would use a fourth-generation fluoroquinolone and for a more severe corneal ulcer, he said it should be scrapped, with initial therapy involving perhaps either kethsol plus fortified aminoglycocide; or, if he thinks it’s gram-positive, he would use fortified vancomycin (various manufacturers) plus an aminoglycocide and perhaps a fourth-generation fluoroquinolone as well.

“Obviously it has to be directed at the appearance of the ulcer, gram stand and culture, and obviously if one is concerned about fungus or herpes then one needs to take a different direction,” Dr. Shugar said.

Editors’ note: Dr. Sheppard has financial interests in the product mentioned. Drs. Shugar and McCulley have no financial interests related to this article.

Contact Information

McCulley: Please contact EyeWorld editorial staff if you would like send correspondence to Dr. McCulley.

Sheppard: 757-622-2200, docshep@hotmail.com

Shugar: 850-584-2778, stareyes@gtcom.net

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