Stronger gatifloxacin OK'd to address pathogen resistance

Salt Lake City-The availability of a new formulation of gatifloxacin ophthalmic solution containing 0.5% active ingredient (Zymaxid, Allergan) will provide ophthalmologists with a valuable option for addressing the growing problem of resistance among some important ocular pathogens, said Randall J. Olson, MD.

Allergan announced May 19 that it had received FDA approval to market its new, more potent formulation of gatifloxacin ophthalmic solution for the treatment of bacterial conjunctivitis.

The product offers the proven broad-spectrum activity of gatifloxacin against common gram-positive and gram-negative ocular pathogens in a preparation containing a two-thirds higher concentration of active ingredient compared with the original formulation, gatifloxacin 0.3% (Zymar, Allergan). Like the original formulation, the new formulation also is preserved with benzalkonium chloride (BAK).

"However, microbiological susceptibility data from a variety of sources clearly show increasing resistance to the fourth-generation fluoroquinolones among some ocular pathogens, particularly methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis," he added. "Fortunately, the topical route of administration used to treat bacterial conjunctivitis provides the opportunity for overcoming higher bacterial minimal inhibitory concentration (MIC) values by achieving a higher concentration of the anti-infective agent in the target tissue through direct delivery."

"Considering that fluoroquinolones are concentration-dependent antimicrobial agents for which therapeutic outcome is dependent on the pharmacokinetic/pharmacodynamic parameter of AUC/MIC for a given pathogen, the pharmacokinetic advantages of gatifloxacin 0.5% should translate into increased clinical efficacy," Dr. Olson said.

The presence of BAK in the new commercially available ophthalmic preparation of gatifloxacin is an additional advantage, because results from a number of studies show that BAK acts together with gatifloxacin to provide increased antibacterial activity, he said.

"In a recently published study from our institution, we reported on the use of scanning electron microscopy to examine visually the antibacterial effects of gatifloxacin alone or with BAK on an ocular isolate of MRSA [J Ocul Pharmacol Ther. 2010;26:133-136]. The results from blinded review of structural changes and mitotic activity visualized in the SEM images showed statistically significant advantages of the combination of gatifloxacin with BAK compared with gatifloxacin alone," Dr. Olson said.

Gatifloxacin 0.5% ophthalmic solution is indicated for the treatment of bacterial conjunctivitis in patients aged 1 year and older for infections caused by susceptible strains of the following organisms: Haemophilus influenzae, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mitis group*, Streptococcus oralis*, and Streptococcus pneumoniae. (*Efficacy for this organism was studied in fewer than 10 infections.) The recommended dosage is one drop every 2 hours in the affected eye(s) while awake, up to 8 times on the first day, and then 2 to 4 times daily while awake on days 2 to 7.