CLINICAL PHARMACOLOGY
Mechanism Of Action
Levofloxacin is a member of the
fluoroquinolone class of anti-infective drugs. (See Microbiology)
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 mcg/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 mcg/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
Corynebacterium species*
Staphylococcus aureus
Staphylococcus epidermidis
Streptococcus pneumonia
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 2 mcg/mL or less (systemic susceptible breakpoint)
against most ( ≥ 90%) strains of the following ocular pathogens:
Aerobic Gram-positive Microorganisms
Enterococcus faecalis
Staphylococcus saprophyticus
Streptococcus agalactiae
Streptococcus pyogenes
Aerobic Gram-negative Microorganisms
Acinetobacter anitratus
Acinetobacter baumannii
Citrobacter koseri
Citrobacter freundii
Enterobacter aerogenes
Enterobacter agglomerans
Enterobacter cloacae
Escherichia coli
Haemophilus parainfluenzae
Klebsiella oxytoca
Klebsiella pneumonia
Legionella pneumophila
Moraxella catarrhalis
Morganella morganii
Neisseria gonorrhoeae
Proteus mirabilis
Proteus vulgaris
Providencia rettgeri
Providencia stuartii
Pseudomonas aeruginosa
Pseudomonas fluorescens
Clinical Studies
In randomized, double-masked, multicenter controlled
clinical trials where patients were dosed for 5 days, QUIXIN® 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%.