Pharmacokinetics:
Levofloxacin concentration in plasma was measured in 15 healthy adult volunteers at various time points during a 15 day course of treatment with Levofloxacin Ophthalmic Solution. The mean levofloxacin concentration in plasma 1 hour postdose, ranged from 0.86 ng/mL on Day 1 to 2.05 ng/mL on Day 15. The highest maximum mean levofloxacin concentration of 2.5 ng/mL was measured on Day 4 following 2 days of dosing every 2 hours for a total of 8 doses per day. Maximum mean levofloxacin concentrations increased from 0.94 ng/mL on Day 1 to 2.15 ng/mL on Day 15, which is more than 1,000 times lower than those reported after standard oral doses of levofloxacin. Levofloxacin concentration in tears was measured in 30 healthy adult volunteers at various time points following instillation of a single drop of Levofloxacin Ophthalmic Solution. Mean levofloxacin concentrations in tears ranged from 34.9 to 221.1 μg/mL during the 60-minute period following the single dose. The mean tear concentrations measured 4 and 6 hours postdose were 17.0 and 6.6 μg/mL. The clinical significance of these concentrations is unknown.

Microbiology:
Levofloxacin is the L-isomer of the racemate, ofloxacin, a quinolone antimicrobial agent. The antibacterial activity of ofloxacin resides primarily in the L-isomer. The mechanism of action of levofloxacin and other fluoroquinolone antimicrobials involves the inhibition of bacterial topoisomerase IV and DNA gyrase (both of which are type II topoismerases), enzymes required for DNA replication, transcription, repair, and recombination. Levofloxacin has in vitro activity against a wide range of Gram-negative and Gram-positive microorganisms and is often bactericidal at concentrations equal to or slightly greater than inhibitory concentrations.

Fluoroquinolones, including levofloxacin, differ in chemical structure and mode of action from β-lactam antibiotics and aminoglycosides, and therefore may be active against bacteria resistant to β-lactam antibiotics and aminoglycosides. Additionally, β-lactam antibiotics and aminoglycosides may be active against bacteria resistant to levofloxacin. Resistance to levofloxacin due to spontaneous mutation in vitro is a rare occurrence (range: 10-9 to 10-10). Levofloxacin has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section:

AEROBIC GRAM-POSITIVE MICROORGANISMS
Corynebacterium species*
Staphylococcus aureus
Staphylococcus epidermidis
Streptococcus pneumoniae
Streptococcus (Groups C/F)
Streptococcus (Group G)
Viridans group streptococci

AEROBIC GRAM-NEGATIVE MICROORGANISMS
Acinetobacter lwoffii*
Haemophilus influenzae
Serratia marcescens*

*Efficacy for this organism was studied in fewer than 10 infections. The following in vitro data are also available, but their clinical significance in ophthalmic infections is unknown. The safety and effectiveness of levofloxacin in treating ophthalmological infections due to these microorganisms have not been established in adequate and well-controlled trials. These organisms are considered susceptible when evaluated using systemic breakpoints. However, a correlation between the in vitro systemic breakpoint and ophthalmological efficacy has not been established. The list of organisms is provided as guidance only in assessing the potential treatment of conjunctival infections.

Levofloxacin exhibits in vitro minimal inhibitory concentrations (MICs) of 2μg/mL or less (systemic susceptible breakpoint) against most (≥90%) strains of the following ocular pathogens:

Aerobic gram-positive microorganisms
Enterococcus faecalis
Streptococcus agalactiae
Staphylococcus saprophyticus
Streptococcus pyogenes

Aerobic gram-negative microorganisms
Acinetobacter anitratus
Legionella pneumophila
Acinetobacter baumannii
Moraxella catarrhalis
Citrobacter diversusi
Morganella morgqanii
Citrobacter freudii
Neisseria gonorrhoeae
Enterobacter aerogenes
Proteus mirabilis
Enterobacter agglomerans
Proteus vulgaris
Enteroacter cloacae
Providencia rettgeri
Escherichia coli
Providencia stuartii
Haemophilus arainfluenzae
Pseudomonas aeruginosa
Klebsiella oxytoca
Pseudomonas fluorescens
Klebsiella pneumoniae 

Clinical Studies:
In randomized, double-masked, multicenter controlled clinical trial where patients were dosed for 5 days, Levofloxacin Ophthalmic Solution demonstrated clinical cures in 79% of patients treated for bacterial conjunctivitis on the final study visit day (day 6-10). Microbial outcome for the same clinical trials demonstrated an eradication rate for presumed pathogens of 90%.

General
As with other anti-infectives, prolonged use may result in overgrowth of non-susceptible organisms, including fungi. If superinfection occurs, discontinue use and institute alternative therapy. Whenever clinical judgment dictates, the patient should be examined with the aid of magnification, such as slitlamp biomicroscopy, and where appropriate, fluorescein staining. Patients should be advised not to wear contact lenses if they have signs and symptoms of bacterial conjunctivitis.

Information for Patients
Avoid contaminating the applicator tip with material from the eye, fingers or other source. Systemic quinolones have been associated with hypersensitivity reactions, even following a single dose. Discontinue use immediately and contact your physician at the first sign of a rash or allergic reactions.

Drug Interactions:
Specific drug interaction studies have not been conducted with Levofloxacin Ophthalmic Solution. However, the systemic administration of some quinolones has been shown to elevate plasma concentrations of theophylline, interfere with the metabolism of caffeine, and enhance the effects of the oral anticoagulant warfarin and its derivatives, and has been associated with transient elevations in serum creatinine in patients receiving systemic cyclosporine concomitantly.

Carcinogenesis, Mutagenesis, Impairment of Fertility:
In a long term carcinogenicity study in rats, levofloxacin exhibited no carcinogenic or tumorigenic potential following daily dietary administration; the highest dose (100 mg/kg/day) was 875 times the highest recommended human ophthalmic dose. Levofloxacin was not mutagenic in the following assays: Ames bacterial mutation assay (S. typhimurium and E. coli), CHO/HGPRT forward mutation assay, mouse micronucleus test, mouse dominant lethal test, rat unscheduled DNA synthesis assay, and the in vivo mouse sister chromatid exchange assay. It was positive in the in vitro chromosomal aberration (CHL cell line) and in vitro sister chromatid exchange (CHL/IU cell line) assays. Levofloxacin caused no impairment of fertility or reproduction in rats at oral doses as high as 360 mg/kg/day, corresponding to 3,150 times the highest recommended human ophthalmic dose.

Pregnancy: Teratogenic Effects. Pregnancy Category C
Levofloxacin at oral doses of 810 mg/kg/day in rats, which corresponds to approximately 7,000 times the highest recommended human ophthalmic dose, caused decreased fetal body weight and increased fetal mortality. No teratogenic effect was observed when rabbits were dosed orally as high as 50 mg/kg/day, which corresponds to approximately 400 times the highest recommended maximum human ophthalmic dose, or when dosed intravenously as high as 25 mg/kg/day, corresponding to approximately 200 times the highest recommended human ophthalmic dose. There are, however, no adequate and well-controlled studies in pregnant woman. Levofloxacin should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers:
Levofloxacin has not been measured in human milk. Based upon data from ofloxacin, it can be presumed that levofloxacin is excreted in human milk. Caution should be exercised when Levofloxacin Ophthalmic Solution is administered to a nursing mother.

Pediatric Use:
Safety and effectiveness in infants below the age of one year have not been established. Oral administration of quinolones has been shown to cause arthropathy in immature animals. There is no evidence that the ophthalmic administration of levofloxacin has any effect on weight bearing joints.

Geriatric Use:
No overall differences in safety or effectiveness have been observed between elderly and other adult patients.