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Quixin

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Quixin

CLINICAL PHARMACOLOGY

Pharmacokinetics

Levofloxacin concentration in plasma was measured in 15 healthy adult volunteers at various time points during a 15-day course of treatment with QUIXIN® 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 2.25 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 QUIXIN® 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 topoisomerases), 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 AEROBIC GRAM-NEGATIVE A MICROORGANISMS
Corynebacterium species* Acinetobacter lwoffii*
Staphylococcus aureus Haemophilus influenzae
Staphylococcus epidermidis Serratia marcescens*
Streptococcus pneumoniae  
Streptococcus (Groups C/F)  
Streptococcus (Group G)  
Viridans group streptococci  
*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 2 μg/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 A MICROORGANISMS
Acinetobacter anitratus Legionella pneumophila
Acinetobacter baumannii Moraxella catarrhalis
Citrobacter diversus Morganella morganii
Citrobacter freundii Neisseria gonorrhoeae
Enterobacter aerogenes Proteus mirabilis
Enterobacter agglomerans Proteus vulgaris
Enterobacter cloacae Providencia rettgeri
Escherichia coli Providencia stuartii
Haemophilus parainfluenzae Pseudomonas aeruginosa
Klebsiella oxytoca Pseudomonas fluorescens
Klebsiella pneumoniae  

Clinical Studies

In randomized, double-masked, multicenter controlled clinical trials where patients were dosed for 5 days, QUIXIN® (levofloxacin ophthalmic solution 0.5%) demonstrated clinical cures in 79% of patients treated for bacterial conjunctivitis on the final study visit day (day 6-10). Microbial outcomes for the same clinical trials demonstrated an eradication rate for presumed pathogens of 90%.

Last reviewed on RxList: 12/18/2008
This monograph has been modified to include the generic and brand name in many instances.

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